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East meets west:
dispersal in the peregrine Falco peregrinus
Ed Drewitt
A dissertation submitted to the University of Bristol in accordance with the requirements for award of the Masters Degree by Research in the Faculty of Science. School of Biological Sciences, December 2019.
Word Count: 14, 280
Abstract
The peregrine is a pan-global species, found in most habitats apart from the polar regions
and deserts. Over the past 30 years it has been recovering from the direct and indirect
effects of organo-phosphate pesticides which severely depleted their populations across
Europe and North America. In Britain, the peregrine’s population dropped below 400 pairs.
While there are now over 1700 breeding pairs in Britain, alongside an unknown floating
population of non-breeding birds, little has been published on the species’ behaviour and in
particular their post-natal dispersal in lowland England. This is the first study of its kind that
outlines the movements of peregrines in southwest England. It reveals that female
peregrines disperse with a north-east bias, dispersing into areas of lower peregrine
occupation, and travelling longer distances than males. They remain in areas of low altitude
with many being recovered at wetland, agricultural and semi-natural habitats. It is likely
many of these birds are non-breeders, especially as only half the number ringed at urban
locations were recovered in an urban environment, while just a fifth originally ringed at
inland quarries were recovered at subsequent quarries. Peregrines show strong fidelity to
the type of nesting habitat where they hatched and therefore these figures suggest many of
the recovered birds were not yet on a territory, were nesting on nearby rural pylons or
sighted while foraging away from a nest site. Overall, the results suggest that peregrines
have the potential to continue occupying suitable and vacant habitats across Britain and
that dispersing birds from the southwest of England are helping to spread the peregrine
population into areas where they have been absent or in low abundance for a long time.
i
Dedication and acknowledgments
A huge thank you to everyone who has provided assistance, expertise and time towards
ringing peregrine chicks, supplying subsequent recoveries and help with the analysis. In
particular I would like to thank: volunteers from the British Mountaineering Council
including Colin Knowles, Daniel Donovan and Simon Fletcher; ringers Hamish Smith, Luke
Sutton, Seb Loram and Jason Fathers; staff from the British Trust for Ornithology, in
particular Mark Wilson and Greg Conway, and supervisors Dr Rob Thomas, Prof. Innes
Cuthill and Dr Sean Rands. A big thanks also to the landowners and stakeholders who have
peregrines nesting on their land and have given permission for ringing activities to take
place.
ii
Sponsorship kindly provided by:
The Bristol Ornithological Club
The Hawk and Owl Trust
Gloucestershire Naturalist’s Society
North Cotswolds Natural History Society
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Author’s declaration
I declare that the work in this dissertation was carried out in accordance with the
requirements of the University's Regulations and Code of Practice for Research Degree
Programmes and that it has not been submitted for any other academic award. Except
where indicated by specific reference in the text, the work is the candidate's own work.
Work done in collaboration with, or with the assistance of, others, is indicated as such. Any
views expressed in the dissertation are those of the author.
SIGNED: ............................................................. DATE:..........................
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Table of contents Chapter 1...........................................................................................................................1
1.1 Introduction............................................................................................................. 1
1.1.1 Why study peregrines?.........................................................................................1
1.1.1.1 An iconic species...........................................................................................1
1.1.1.2 Expanding population and declines in the north..........................................1
1.1.2 The peregrine’s background.................................................................................2
1.1.2.1 The falcon family..........................................................................................2
1.1.2.2 Range............................................................................................................3
1.1.2.3 A species ideal for studying..........................................................................3
1.1.2.4 The wanderer...............................................................................................3
1.2 Researching peregrines............................................................................................4
1.2.1 Defining urban and rural peregrines.....................................................................5
1.2.1.1 What do we mean by an urban or a rural peregrine?...................................5
1.2.1.2 Rural locations close to towns and cities......................................................5
1.2.1.3 Urban kestrels vs urban peregrines..............................................................6
1.2.1.4 The rise of urban peregrines.........................................................................6
1.3 Setting the scene: the peregrine’s relationship with people.....................................7
1.3.1 Ice-age Britain: the southwest..............................................................................7
1.3.2 Persecution...........................................................................................................7
1.3.3 The DDT era..........................................................................................................8
1.3.4 UK protection.......................................................................................................8
1.4 Studying the dispersal of peregrines in southwest England.....................................9
1.4.1 What do we know about the dispersal of peregrines so far?...............................9
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1.4.1.1 In Britain.....................................................................................................10
1.4.1.2 In Europe....................................................................................................12
1.4.1.2.1 Germany.................................................................................................12
1.4.1.2.2 Spain.......................................................................................................13
1.4.1.2.3 Italy: Sicily...............................................................................................13
1.4.1.2.4 Sweden...................................................................................................14
1.4.1.3 In the USA...................................................................................................14
1.4.2 How does my research add to this?...................................................................18
1.5 Replicating my studies............................................................................................18
Chapter 2.........................................................................................................................19
Dispersal of peregrines in the southwest of England........................................................19
2.1 Introduction........................................................................................................... 19
2.1.1 Dispersal of peregrines post-fledging.................................................................19
2.1.1.1 What do we know?.....................................................................................19
2.1.2 What gap is there to fill?....................................................................................20
2.1.3 Predictions and expectations.............................................................................20
2.2 Methods.................................................................................................................21
2.2.1 Field work and colour-ringing.............................................................................21
2.2.1.1 Defining habitats........................................................................................21
2.2.2 Study areas.........................................................................................................21
2.2.3 Defining recoveries.............................................................................................22
2.2.4 Data handling and analysis.................................................................................22
2.3 Results....................................................................................................................23
2.3.1 Where are young peregrines being recovered?.................................................23
....................................................................................................................................... 24
2.3.2 What directions are dispersing peregrines travelling in?...................................28
2.3.3 What elevation are peregrine dispersing to?.....................................................30
2.3.4 What habitats are peregrines dispersing to?......................................................32
2.3.5 Specific Case Studies..........................................................................................33
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2.3.5.1 Avon Gorge.................................................................................................33
2.3.5.2 Town hall, Bournemouth............................................................................34
2.3.5.3 Scabbacombe, Devon.................................................................................34
2.3.6 Additional sightings of interest...........................................................................34
2.3.6.1 West Bay, Dorset........................................................................................34
2.3.6.2 St John’s Church, Bath................................................................................34
2.3.6.3 Halifax.........................................................................................................34
2.3.6.4 Morocco.....................................................................................................34
2.4 Discussion...............................................................................................................35
2.4.1 Peregrine dispersal.............................................................................................36
2.4.1.1 Density dependence considerations...........................................................39
2.4.1.2 Floaters.......................................................................................................40
2.4.1.3 Cooperative Breeding.................................................................................41
2.4.1.4 Specific nesting habitats.............................................................................42
2.4.2 Why is this latest research on peregrines important?........................................43
2.4.3 Biases or limitations...........................................................................................44
2.4.3.1 Natal dispersal data vs general dispersal data............................................44
2.4.3.2 Nest locations.............................................................................................45
2.4.3.3 Recoveries and observations......................................................................45
2.4.3.4 Reliance on other people............................................................................45
2.4.3.5 Handling chicks...........................................................................................46
2.4.3.6 Fitness of birds............................................................................................46
2.4.3.7 Rehabilitated birds.....................................................................................46
2.4.4 Next steps...........................................................................................................46
2.5 Bibliography...........................................................................................................48
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List of table and figures
Table
Table 1.1. A summary table of dispersal by peregrines amalgamated from Dennhardt &
Wakamiya (2013), Wegner (2017) and additional data from other published papers
(indicated in the table)...........................................................................................................16
Figures
Figure 2.1. Arrows joining locations of ringing with locations of recovery: blue = location
where peregrines were ringed as chicks; red = location where the same peregrines have
been recovered......................................................................................................................24
Figure 2.2. 95% kernels overlaid on a map of England and Wales: blue = location where
peregrines were ringed as chicks; red = location where peregrines have been recovered.
Clearly, ringing locations in the sea are impossible, but recoveries could be (death at sea). 25
Figure 2.3. Boxplot comparing the distances travelled by known sex birds and unknown: F =
female (n=24); M = male (n=21) and U = unknown sex (n=1). Thick horizontal bars are
medians, the boxes span the interquartile range, ‘whiskers’ extend to the first point within
1.5 interquartile ranges from the nearest quartile, and circles (lying outside the whiskers)
are flagged as potential outliers. However, without independent evidence that the data are
unreliable, there is no reason to remove outliers..................................................................26
Figure 2.4. Box plot comparing the duration in which peregrines were recovered after being
ringed as chicks: F = female (n=24); M = male (n=21) and U = unknown sex (n=1). Boxplot
description as in Figure 2.3....................................................................................................27viii
Figure 2.5. A rose diagram showing the direction of travel for male and female peregrines
(n=32), Rayleigh test of deviation from uniformity: Z = 0.47, P<0.001...................................28
Figure 2.6. A rose diagram showing the direction of travel for male peregrines (n=15),
Rayleigh test of deviation from uniformity: Z = 0.38, P=0.093...............................................29
Figure 2.7. A rose diagram showing the direction of travel for female peregrines (n=16),
Rayleigh test of deviation from uniformity: Z = 0.55, P=0.001...............................................29
Figure 2.8. Bar chart showing the elevation of 1km squares from across the UK (Source:
https://biogeo.ucdavis.edu/data/diva/msk_alt/GBR_msk_alt.zip)........................................30
Figure 2.9. Bar chart showing the elevation at which peregrines were ringed (n=46)...........31
Figure 2.10. Bar chart showing the elevation at which peregrines were recovered (n=46)...31
Figure 2.11. Bar chart comparing the nesting habitat that peregrines were ringed in and
subsequently recovered in after 12 months or more. Peregrines recovered in areas away
from immediate nesting habitat were excluded, for example, wetlands. Numbers above
each bar represent the actual percentage calculated............................................................32
Figure 2.12. Bar chart comparing the local habitats were peregrines hatched and where they
were recovered based on the Corine land cover data set. Numbers above each bar represent
the actual percentage calculated...........................................................................................33
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Chapter 1
1.1 Introduction
1.1.1 Why study peregrines?
1.1.1.1 An iconic species
Peregrines, Falco peregrinus, are the fastest bird in the world, capable of reaching speeds of
402km per hour (250 mph) in a free-fall stoop flight to catch prey (Tucker 1998). Their fast speed,
predatory prowess, engaging and large forward-facing eyes and long history with falconry, make
peregrines a popular bird with people all around the world (Drewitt, 2014; Granot et al.,2014;
Pagel et al., 2018).
Despite their popularity, peregrines, like many raptor species, have been the target of illegal
persecution for hundreds of years. With numbers suppressed, their population dwindled in the
UK – and disappeared completely in many parts of Europe and North America - due to the effects
of chemical pesticides used in the 1950s and 1960s. Since the ban of the chemicals and greater
protection, peregrines are increasing across their range, reaching population levels that have not
been witnessed in recent times.
1.1.1.2 Expanding population and declines in the north
In southern England, peregrines have been expanding their population, particularly in the west,
and with new individuals and pairs appearing in the east and north of the country (Wilson et al.,
2018). This equates to a 200% range expansion since the period 1968–1972 (Balmer et al., 2013).
Peregrines are now common in towns and cities nesting on manmade nesting platforms that
have been put there for them. Despite this comeback some peregrine populations in Britain are
declining, particularly in northern England and Scotland where there have been some local
extinctions. This is thought to be due to illegal persecution, wetter spring weather (causing chicks
to chill) and decline in the quality of habitat and its associated bird species that are prey for
peregrines (Balmer et al., 2013; McGrady et al., 2017; Newton, 2017; Wilson et al., 2018).
Environmental pollutants and inter-specific competition for breeding sites or prey may also have
some influence (Wilson et al., 2018). Despite this setback, the peregrine’s success across much of 1
England is likely due to the connectivity that towns, cities, quarries, pylons, coastal cliffs criss-
crossing England offer. Combined they provide a large mosaic of suitable habitats for feeding,
roosting and nesting, even though the wider countryside, woodlands and wetlands in these areas
are showing declines in biodiversity (Saura, Bodin and Fortin, 2014; Newton, 2017; DEFRA, 2018;
Wilson et al., 2018).
Peregrines colonising towns and cities in Britain over the past 20 years have followed a pattern of
urbanisation, a phenomenon first reported by Taranto (2009) in Italy and diagnostic of peregrines
first appearing at urban locations. This begins with a single bird regularly using a building during
the autumn/winter months through to early spring. A second bird may join it a year or two later
followed by signs of courtship and display. If a suitable nest ledge is available, they will attempt
to nest and, on some occasions, they will attempt to nest on unsuitable substrate where the eggs
roll into the gutter. At many sites where a suitable ledge isn’t available, local people and business
have put up nest boxes which have been readily taken by the peregrines. Many breeding urban
peregrines across the UK have nest boxes to thank for their success.
The peregrine’s population success in the south of England raises questions as to where new
birds in other parts of Britain are colonising from. With continuing threats to their survival in
some parts of Britain there is a need to discover in more detail where their young disperse after
fledging and how this will influence their population distribution, particularly if some of these
threats, such as illegal persecution, increase or are reduced in the long term.
1.1.2 The peregrine’s background
1.1.2.1 The falcon family
Peregrines Falco peregrinus are large crow-size falcons with barrel-shaped bodies and long,
pointed wings. They are members of the genus Falco – family Falconidae and sub-family
Falconinae - and share Britain with other members of this group, the kestrel Falco tinnunulus, the
merlin Falco columbarius and the summer-visiting hobby Falco subbuteo. They share
characteristics including long pointed wings, strong hooked beaks with a small tomial tooth,
sharp talons and excellent eyesight (Drewitt, 2014). The Falconidae have recently been re-
positioned taxonomically to sit alongside parrots, which are now their sister group, between
woodpeckers and passerines (Sangster et al., 2013).
2
1.1.2.2 Range
Peregrines are found across the world apart from the Arctic, Antarctica and desert areas. In
deserts and forest-steppe they are replaced by other raptors, such as the saker Falco cherrug
(Ferguson-Lees and Christie, 2001). When nesting, their range is thought to cover over 40% of
the Earth’s land mass (White et al., 2013).
1.1.2.3 A species ideal for studying
Peregrines are a predictable and approachable species - particularly in urban areas - favouring
locations where they are likely to be seen on a regular basis. This allows to them be easily studied
in town and cities as well as rural locations such as coastal cliffs and quarries. They are attracted
to relatively accessible and open locations where members of the public can visit or watch them
at home or work via web cameras and the internet. Between 2009 and 2012, the Royal Society
for the Protection of Birds (RSPB) hosted a mean of 11 peregrine ‘A date with nature’ events per
year. These involved showing the public peregrines at urban locations in cities such as
Manchester and London. The charity engaged with a mean of 116, 000 people per year (pers.
comm. Richard Bashford, RSPB). This is all despite their population in the UK being far lower
compared to other common raptors such as buzzards Buteo buteo (67, 000 pairs), kestrels (45,
000 pairs) and sparrowhawks (33, 000 pairs) (Robinson, 2018). In the UK there are estimated to
be 1,769 pairs of peregrines plus tens or hundreds of non-breeding ‘satellite’ birds (Wilson et al.,
2018).
1.1.2.4 The wanderer
The peregrine’s Latin name, Falco peregrinus, means wandering falcon. This is indicative of this
species’ long-distance seasonal movements across much of its range. During the autumn across
vast swathes of North America, Northern Europe and Siberia, peregrines leave behind their
summer habitats that become dark and frozen during the winter. They head for temperate or
tropical climates following their prey - almost entirely birds – which also travel south to warmer
climes. For example, peregrines move between Alaska and South America (Chile, Peru, Bolivia),
and Arctic Russia to Iraq, India and Bangladesh (Ratcliffe, 1993; Dixon, Sokolov & Sokolov, 2012;
White et al., 2013). In Europe, those nesting in northern Scandinavia migrate south through
Europe, spending their winter across milder parts of the continent, some making it as far south as
Northern Africa (Lindberg, 2009b; Ollila, 2009; White et al., 2013; Drewitt, 2014). These birds
3
perform leapfrog migration, migrating further south than those breeding in south Scandinavia,
which travel shorter distances.
Unlike the five most northern races found across mainland Europe, Asia and North America,
Britain’s peregrines, F.peregrinus peregrinus, do not make long-distance migrations (Ratcliffe,
1993). Prevailing westerlies ensure Britain remains mild during the winter compared to northern
parts of Europe, meaning many birds do not migrate out of the country and ensuring a constant
supply of prey. They move short distances as a partial migrant from their breeding grounds or
natal sites to habitats such as wetlands where they seek prey, only sometimes crossing the
English Channel to France and the Low Countries (White et al., 2013). Only 6.5% move more than
200km while 78% move less than 100km (Ratcliffe, 1993; Wernham et al., 2002).
When Britain’s weather does become cold and freezing Peregrines are survivors even though
their food can virtually disappear. During sudden spells of freezing temperatures and blanket
snow cover, prey such as ducks, waders and small birds make sudden movements out of an area,
leaving peregrines with little to hunt. Lapwings (Vanellus vanellus), golden plovers (Pluvialis
apricaria) and skylarks (Alauda arvensis) make rapid cold weather movements travelling as far
south as France, Spain and Portugal overnight (Kirby and Lack, 1993; Wernham et al., 2002;
Newton, 2010). Peregrines overcome this by storing food in a cache. Crevices in rocks or ledges
on buildings can be piled with dead birds, many of which go uneaten. On buildings these
sometimes fall to the ground during windy weather and remain unrecovered by the peregrines
(Ratcliffe, 1993; Drewitt, 2014).
1.2 Researching peregrines
As peregrines have made towns and cities their home during the past 20 years, they have
become more accessible as a study subject for researchers. Before the mid-nineties peregrines
were mainly found in remote, rural locations such as sea cliffs and upland quarries. Here,
observing behaviour posed challenges with researchers navigating the terrain, weather,
disturbance distances and overall practicalities of approaching and visiting nest sites. Today,
urban peregrines provide easier opportunities to be studied, nesting in accessible locations that
can be more easily visited and have cameras fitted. Here they are much less bothered by people
4
and anecdotally disturbance distances are much shorter than for their rural counterparts based
on expert opinion (Ruddock & Whitfield, 2007; Whitfield et al., 2008).
1.2.1 Defining urban and rural peregrines
1.2.1.1 What do we mean by an urban or a rural peregrine?
Chamberlain et al. (2009) classify non-urban/rural environments as natural or semi-natural
environments, including woodland and open country. They define urban environments as places
where buildings dominate and include residential habitats with green spaces such as parks,
gardens and small urban woods.
For my own studies I have defined urban peregrines as those individuals which are spending time
in an urban environment, such as a city, town or industrial building. This may be during an
autumn-winter-spring period, during a breeding season, or both combined. Rural peregrines are
those breeding in a non-urban environment and generally remaining in the countryside all year
round. A peregrine may start life in a rural quarry or coastal cliff location and move into a town
or city to breed, where it becomes an ‘urban peregrine’. The opposite may also happen where
rural peregrines start life as an urban peregrine or use urban areas out of the breeding season.
1.2.1.2 Rural locations close to towns and cities
Peregrines may nest in what can be described as a rural location within close reach of suburbia or
a city centre. For example, a pair that nest in the Avon Gorge is less than 0.5 kilometres from
suburbia and a busy road close to the cliff site. For the purpose of my studies, urban peregrines
have been classed as those in the centre of an urban location such as Bath city. Rural, or semi-
rural peregrines have been defined as those in a quarry or gorge, surrounded by or looking out
onto natural or semi-natural habitats, with some suburbia or villages close by.
In the British Trust for Ornithology’s (BTO) latest paper on the 2014 survey of peregrines (Wilson
et al., 2018), they use the term human structures for urban or man-made locations, and split this
further into buildings, pylons and other structures. Natural sites were classed as natural inland
and natural coastal and classified further depending on their rock or cliff structure and size, while
quarried were subdivided into working and disused.
5
Kettel et al. (2018) refer to urban locations as located in towns and cities with at least 50% urban
or suburban landcover within 2km-radius of the nest site, while rural locations comprise sites
outside of towns and cities that contain no more than 10% urban or suburban land-cover with
2km-radius of a nest site.
1.2.1.3 Urban kestrels vs urban peregrines
The kestrel has until relatively recently been the more common, default falcon in towns and
cities in the UK. Across Europe it is still common in the centre of urban areas including major
cities in countries such as France, German, Romania, Hungary, Italy and Poland (Salvati et al.,
1999; Kübler et al., 2005; Zmihorski & Rejt, 2007). At times it may have been confused as a
peregrine in the early days. While the peregrine population has grown by 50% in England
between 1995 and 2016, the kestrel’s has declined by 20% (Harris et al., 2018). Preliminary work
suggests this is due to changing agricultural practises and the use of rodenticides (Clements,
2008; RSPB, 2018), although goshawk predation is to blame in Kielder Forest, Northumberland
(Petty et al., 2003).
1.2.1.4 The rise of urban peregrines
The phenomenon of peregrines using buildings on a regular basis in the UK is a relatively new
one, pertinent to the past 30 years. However, there are early records of peregrines using
Salisbury Cathedral from 1864/1865 onwards and St Paul’s Cathedral in the early to mid 1900s,
(LNHS, 1964; Ratcliffe, 1993; Drewitt, 2014). There were 21 records from across the UK between
1840 and 1992, ranging from Belfast gas works in Northern Ireland (1980s) to the Post Office
Tower in Swansea in 1990 (Ratcliffe, 1993). The use of man-made structures has been longer
standing across Europe, North America and Africa, ranging from castles, towers and even the
Egyptian pyramids (Ratcliffe, 1993). One of the most iconic nests in North America was in
Montreal, Canada, where successive birds nested on the Sun Life Building between 1936 and
1952 (Ratcliffe, 1993).
In the west of England peregrines began appearing on buildings in urban locations from the mid-
nineties onwards. During this period our knowledge and experience of this species in the UK was
mainly restricted to rural breeding birds; those living in the countryside on rocky crags and cliffs
away from human habitation. In 1993, Derek Ratcliffe, who wrote the most in-depth scientific
monologue, Peregrine Falcons, only devoted two pages out of the 450 to peregrines using
6
buildings! The first research to come from urban peregrines in England was done by John Tully, a
local ornithologist in Bristol, who wrote the first published paper on the diet of urban-dwelling
peregrines in the UK (Tully, 1998).
In other parts of Europe, urban-dwelling peregrines were also being studied at this time, and one
much earlier study on the peregrine’s diet in Berlin, Germany, was published in 1989 (Sömmer,
1989). Other studies, also on peregrine diet and prey, included those from Poland (Rejt, 2001),
Italy (Serra et al., 2001), the Czech Republic (Mlikovsky & Hruska, 2000) and France (Marconot,
2003) where urban-dwelling peregrines were just appearing.
1.3 Setting the scene: the peregrine’s relationship with people
1.3.1 Ice-age Britain: the southwest
Many traditional cliff-nesting sites in Britain currently being used by peregrines may have been
used by successive generations for hundreds of years and records for Lundy Island, in the Severn
Estuary, date back to 1243 (Ratcliffe, 1993). At Cheddar Gorge, where peregrines sometimes
nest, ancient remains from Gough’s Cave date back to 14, 700 years ago and have been found in
association with horse Equus ferus, red deer Cervus elaphus and human remains (Ashton, 2017).
Ptarmigan Lagopus mutus and red grouse Lagopus lagopus, prey for peregrines, indicate the
habitat nearby would have been moorland and open country. As we come up to more recent
times, in the Birds of Somersetshire (1869), the author Cecil Smith explains that the peregrine
falcon is scarce throughout England due to the ‘destructive propensities of gamekeepers’. He
says, “A few pairs, however, continue to breed in different parts of this county. One pair, I have
been informed, bred (and I believe continue to breed) on Brean Down, near Weston-super-
Mare.” Cecil describes its diet as comprising pigeons, partridges, ptarmigan, grouse, ducks, and
various species of sea-fowl and also makes reference to rabbits and young hares forming part of
its diet.
1.3.2 Persecution
While peregrines were revered during the Middle Ages as the ‘sovereign’s or the nobleman’s
hawk’ and protected by harsh penalties (Ratcliffe, 1993), it became a target of persecution during
7
the late 1700s onwards when the fashion of game estates and land enclosure became the vogue.
Animals regarded as vermin included peregrines, alongside other raptors, mammals such as foxes
and stoats, and even medium-size birds such as woodpeckers (Ratcliffe, 1993; Shrubb, 2013;
Howard, 2016). During the Victorian era, peregrines were killed for taxidermy and during the
Second World War they were shot to stop them intercepting carrier pigeons transporting
important messages – peregrines subjected to this cull can be found as study skins in the bird
collection at the Natural History Museum, Tring, Hertfordshire (Ratcliffe, 1993).
1.3.3 The DDT era
During the 1950s peregrines then suffered, like many raptors across the globe, from the effects
of organophosphate pesticides such as dichloro-diphenyl-trichlorethane (DDT) and cyclodenes -
including aldrin and dieldrin - used on crops as insecticides. Seeds and leaves were laced with
these chemicals. Peregrines ate birds such as woodpigeons Columba palumbus which had been
feeding on the affected crops. The pesticides accumulated in the bodies of peregrines and the
result was twofold; some peregrines died directly from the toxicity of cyclodenes or from the
gradual bioaccumulation of pesticides such as DDT. However, the bioaccumulation of DDT and
dichloro-diphenyl-dichloroethylene (DDE), a derivative of DDT, caused the eggshells of
peregrines, and other raptors, to become very thin, resulting in falcons laying eggs that broke
under their own weight (Ratcliffe, 1967; Ratcliffe, 1970). The story has been most recently
summarised in Ratcliffe (1993), McGrady et al. (2017) and Smith et al. (2015), and in Germany in
Schilling & Wegner (2001).
The decline in successful breeding attempts alongside centuries of persecution saw peregrine
populations nosedive in the UK, across Europe and North American; in the UK 355 breeding pairs
remained – 44% of the ‘normal level’ - with only six pairs in southern England (Ratcliffe 1993).
Once the association with DDT and its related chemicals was discovered they were banned from
use. By the early 1980s peregrines slowly began to recover, with increased reproductive success
and a sharp rise in their populations from the 1990s onwards (Ratcliffe, 1993; Sielicki et al., 2009;
McGrady et al., 2017).
8
1.3.4 UK protection
Like other wildlife in the UK, peregrines are protected under the 1981 Wildlife and Countryside
Act and have further protection during the breeding season through additional schedule 1.1
status (“birds protected by special penalties at all times”; Legislation.gov.uk, n.d.). This was
afforded due to their vulnerable population status. Although there are ongoing threats from
illegal persecution, changing prey abundances and habitat degradation, peregrines in the UK are
at their highest population since records began and probably the most for hundreds of years
(Wilson et al., 2018). Despite this, there isn’t room for complacency and, as discussed in section
1.1.1.2, there are concerning gaps and declines in their population in northern England and
Scotland as well as parts of north Cornwall, Wales and Northern Ireland (McGrady et al., 2017;
Newton, 2017; Wilson et al., 2018; Steve Watson pers. comm.).
1.4 Studying the dispersal of peregrines in southwest England
As peregrine populations have recovered there has been a greater opportunity for people to
watch and study peregrines, particularly in urban locations. Surveyors and enthusiasts are able to
keep records of the nesting cycle for the BTO’s nest record scheme and ringers have been able to
access more nests to ring chicks with unique metal BTO rings to see where peregrines turn up at
a later date. Large birds like peregrines are better detected with the use of colour rings, both
from a distance through binoculars and cameras and if found dead on the ground. Since 1998
colour rings have been issued by ringers running particular projects across different regions of
the UK as well as for ringers ringing at single, opportunistic nest locations (pers. comm. Jez
Blackburn, BTO).
One of these projects has been colour-ringing peregrine chicks since 2007, covering urban and
rural sites across the southwest of England, from Gloucestershire to Devon and Dorset to
Wiltshire. It is from this project that over 50 recoveries - dead birds, injured birds and resightings
of live individuals - have been recorded at locations post-fledging, and most of which feature in
the research for this thesis. Analysing these data is the first comprehensive analysis of any colour
ringing project in Britain.
9
1.4.1 What do we know about the dispersal of peregrines so far?
Studying the recoveries of colour-ringed peregrines involves looking at their natal dispersal, the
movement(s) they have made from their hatch site to their breeding territory (Greenwood and
Harvey, 1982). Many of the recoveries in this study do not involve birds recovered (found dead,
injured or resighted) on their breeding territories; they appear to involve individuals that are still
in the process or dispersal or during the non-breeding season. Therefore, this study involves
looking at both natal dispersal and general dispersal of individuals.
1.4.1.1 In Britain
Most of what we know about the dispersal of peregrines in Britain relates to rural birds and from
ringing efforts by the Scottish Raptors Groups and individuals across the UK, particularly Scotland
and northern England (Mearns & Newton, 1984; Ratcliffe, 1993; Morton et al., 2018). Mearns
and Newton (1984) examined data from a peregrine population in the south of Scotland and
established that females dispersed greater distances than males, moving farthest in their first
years of life and noted that birds did not disperse in any particular direction. This fits with their
general behaviour that male peregrines establish territories and females move around looking
for unpaired males. There was no preference to a particular type of breeding location based on
where they hatched; for example, a chick hatched on a coastal cliff may subsequently be found
breeding on an inland cliff. For ringed birds trapped while breeding, males were found to be a
maximum of 75km (median 20km, n=15) from where they were originally hatched and ringed,
while females were found within 185km (median 68km, n=24). Birds found dead by members of
the public were found at greater distances from where they hatched: the longest travelled males
reached 357km (n=11) and females 324km (n=24) with median values of 58km for males and
83km for females.
Ratcliffe (1993) discusses dispersal as part of the wider movements of peregrines. He features an
analysis by Chris Mead, British Trust for Ornithology (BTO), who outlines the recovery
movements of ringed peregrines. As with other research, his analysis reveals females are more
likely to move further than males and that individuals don’t disperse in any particular direction.
He also notes that first-year peregrines on average made shorter movements than adults,
although also refers to Mearns & Newton (1984) where the opposite was found. However,
although his analysis goes into detail, it is difficult to distinguish any meaningful information
10
about natal dispersal as much of the data includes cherry-picked examples or data where
individuals were ringed at the chick or adult stage. Despite this, the paper highlights that:
7% of recoveries comprising birds ringed as chicks were found over 200km away.
Out of a sample of 358 birds, which includes some ringed as adults, 49% were found
within 50Km of the ringing sites, 25% between 50 and 99km and 18% at 100 – 199km.
In Smith et al. (2015), their focus of research is about survival and fidelity, and in their discussion
found that as the peregrine population grew in their study area (South Scotland and the North
England), juveniles dispersed further as there were fewer territories available for them to
occupy. Their fidelity to the study area was lower when the peregrine population became denser.
Morton et al. (2018) have provided a comprehensive paper examining the dispersal of
peregrines. They do this on a local scale in Scotland and northern England over two time periods,
when the peregrine was at a low density and when it was at a high density. They also examined
national data of peregrine recoveries spanning 50 years up to 2016. It is a particularly valuable
paper because it examines ringing data from across the UK population rather than just at a local
level where peregrines may behave differently. They found that sex of a peregrine determined
how far it dispersed after it had fledged and not population density, with females moving further
than males. However, as territories across a wide area become saturated there is nowhere for
the young birds to disperse to; therefore, the benefits of travelling long distances become less
relevant. They argue against the idea of a mate-finding Allee effect (a correlation between mean
individual fitness and population size; Courchamp et al. 2004) being at play as both male and
female peregrines showed reduced dispersal distances in the later years. They also make
reference to the fact that larger females are more likely to disperse greater distances, aligning
with evidence that larger bodied animals disperse greater distances. Like earlier studies, on a
local scale, they found no evidence of peregrines dispersing in any particular direction that
differed from a uniform distribution. However, the national data did reveal a northerly bias
influenced by dispersing male peregrines.
What is less apparent in this paper is how different habitats may influence peregrine dispersal,
for example, in eastern Germany, fidelity to nest site locations may influence the dispersal of
peregrines. Male peregrines reared in tree nests largely remain tree-nesting birds and may
account for the absence of cliff and pylon-nesting peregrines nesting close to the edge of the
11
forests as they are not choosing these environments as a nesting territory (Kleinstäuber et al.,
2009).
One further paper, Lensink (1997), looks in detail at the range expansion of raptors in Scotland
and the Netherlands, using Mearns & Newton (1984) as his main reference point for the
dispersal of peregrines. Of particular interest is the velocity at which raptors, including
peregrines, increased their range. Last century, peregrines showed the greatest velocity of range
expansion in Scotland and particularly in Wales. Referring to this research may provide insights
into the rate at which young peregrines from the west of England are dispersing to new currently
unoccupied territories in eastern and northern England.
1.4.1.2 In Europe
1.4.1.2.1 Germany
While colour ringing peregrines in the UK is an expanding activity, in Germany extensive and
thorough colour ringing studies have already been conducted. Here a huge majority of hatched
peregrine chicks have been colour-ringed allowing for a much faster understanding of what
peregrines do; for example, in Germany, 3, 500 chicks had been ringed up to the end of 2018
(Peter Wegner pers. comm.). By colour ringing so many young there is a large sample size,
leading to greater recoveries. This also means that as these young birds begin to breed, all their
life histories are known. Peter Wegner and his team have been studying peregrines for at least
three decades and have access to a huge database (Peter Wegner pers. comm.). For example, of
these chicks ringed, 340 have subsequently been found dead and an additional 480 individuals
have been identified in the field through their colour rings. His most recent paper (Wegner, 2017)
summarises his team’s 30 years of work in the North Rhine-Westphalia state of western Germany
where 95% of the 220 pairs of peregrines breed on industrial buildings at a ratio of 30:1
(buildings vs rocks/cliffs). The movements of juvenile birds are limited, with young birds mainly
wintering in the Netherlands, Belgium, northern France, with only a few migrating more than
250km. His ringing recoveries reveal that male peregrines show philopatry behaviour, settling
near where they hatched; 50% of adult males settle at distances between 0km and 20km from
where they hatched. To the other extreme, Peter and his team have found that some female
peregrines will settle up to 550km from where they hatched, without any preference for
direction. Many have been found across Germany, while two females set up nests in Poland and
12
a large portion are found breeding in the Netherlands. The adult male peregrines choose the
nesting habitat which initially, when the population was increasing, was a problem for females.
Males dispersed very short distances and females dispersed greater distances, finding suitable
breeding habitat with no males to breed with. Females generally disperse between 80 and
150km from where they hatched. The mean settlement distance of male peregrines was 39km
(range 0 – 290km) while for females it was 111km (range 10 – 550km). Between the periods
1991- 2001, when the peregrine population was increasing, and 2002 – 2012, when there was a
strong concentration of migrant birds appearing, the males’ settlement distance dropped from
48km to 37km. This is thought to be density dependent. There was no change for females.
Wegner compares this density dependence effect with the Netherlands (van Geneijgen, 2014)
where the mean settlement distance reduces for both males (75km to 47km) and females
(149km to 112km) between the periods 1990 – 2008 and 2008 – 2013. Another study in Germany
(Rockenbauch, 2002) also shows a reduction in male dispersal distance (65km to 49km) from up
to the 1990s to after 1991. Females on the other hand increased slightly from 116km to 124km in
the same periods, perhaps as they travel further to find vacant territories as local habitats
become saturated. Wegner’s paper also compares range and distances with Scotland, Alaska, the
US Midwest, other parts of Germany, the Netherlands and Spain.
1.4.1.2.2 Spain
In Spain, research by (Zuberogoitia et al., 2009) reveals that juvenile peregrines begin dispersing
with in the first month of leaving their nest. Females travelled 5.5km, 9.3km and 47.5km from
where they hatched; two males travelled 68km and 32.3km. The adventurous young birds came
back to their nests within that period. Pre-breeding dispersal revealed no statistical differences
between males and females (mean respective distances 51.8km and 80.1km). Once known birds
were breeding, the mean distances were 64.5km for males and 108.5km for females. As with
other studies females moved further than males.
1.4.1.2.3 Italy: Sicily
Most recently in Sicily peregrines fitted with satellite transmitters have revealed that peregrines
disperse in a non-random direction, with juveniles heading off towards 102°E and overall
movements (dispersing juveniles and wanderers) towards a NNE-ESE direction. The research
13
team split peregrine movements into three groups: the post-fledging dependence period (PFDP),
the wandering and the wintering period (Bondì et al., 2018).
1.4.1.2.4 Sweden
In Sweden, Peter Lindberg looked closer at natal dispersal in peregrine during the 1990s
(Lindberg, 2009b). Here both captive-released and wild peregrines were colour-ringed and
monitored with no significant differences found between the dispersal of birds from either
group. Male peregrines travelled shorter distances than females, with medians of 46km (range 6
– 206km) and 137km (range 13 – 425km) respectively. Natal dispersal maps showing the
journeys taken by peregrines in 2006 - 2007 are summarised in this paper revealing links
between populations in southwest Sweden, central Sweden, Denmark and northern Germany,
with females maintaining gene flow between these local populations by their longer dispersal
distances.
1.4.1.3 In the USA
Most studies on dispersal of peregrines have been done in the USA and Mexico, where many
reintroduced peregrines have been the subject of detailed research to see how these birds fare
against wild-hatched peregrines. Peregrines studied in North America are of different sub-species
(F.p. anatum, F.p.pealei and F.p.tundrius) although their exact taxonomy continues to be debated
(White et al., 2013). Unlike peregrines in the UK, these birds follow long migrations from as far
north as Alaska and take up winter home ranges in Mexico and south into South America,
including Chile, Peru and Argentina.
In the USA, peer-reviewed papers focusing on the dispersal of peregrines focus largely on the
differences between wild and ‘hacked’ young birds. Hacked peregrines are placed into a hacking
cage in the area where they will be released. After a period of time the door is opened and the
young birds are free to fly, returning if they wish to a ready supply of food. As the peregrines
adjust to their new surroundings they return less and less to the food until they are independent.
The recovery of peregrines after the period and effects of DDT was possible due to the efforts of
reintroducing birds.
In many cases peregrines have been fitted with satellite tags, giving accurate information on the
location and movements of individuals. While direct comparisons are less useful between a
migratory population and a non-migratory population, results from peregrines studied in North 14
America do provide some useful insights. Dennhardt & Wakamiya (2013) studied the natal
dispersal distances travelled by both wild and reintroduced peregrines (through hacking) in the
upper Midwest, USA and summarised the dispersal distances of peregrines from other studies in
Alaska, Scotland, Midwest, USA and Greenland (Ambrose & Riddle, 1988; Newton & Mearns,
1988; Tordoff & Redig, 1997; Restani & Mattox, 2000) (see Figure 1.4.1.4). Mean dispersal
distances ranged from 354km (Midwest) to 27.1km (Greenland) for females and 174km
(Midwest) to 28.1km (Greenland) for males. Those in Alaska were 121km for females and 69km
for males.
In Pennsylvania in eastern North American females peregrines disperse significantly further than
males (337.7km and 161.4km respectively) and with no statistical differences between those
fledging from buildings and bridges or density dependence effects on natal dispersal (Katzner et
al., 2012).
In their own studies, Dennhardt & Wakamiya (2013) found the mean dispersal distance was
226km for females and 108km for males, with one female travelling up to 876km. The majority of
young birds headed off in a northwest or southeast direction, towards big towns or cities, or
large areas of water. They made some important observations which can be considered
alongside the dispersal behaviour of peregrines in the UK. In particular that:
female peregrines travel up to twice the distance of males;
the distances male disperse to may be limited by the number of males already on
territories, available nest sites in different habitats and how close potential nest sites are
to one another.
they found that the mean effective dispersal distance was shorter than in other studies
and that individuals peregrines congregate in similar areas, for example, where there is a
good supply of food.
In Dubuque, Iowa, USA, 38 juvenile peregrines were fitted with radio-telemetry tags in 1999 and
2000. These individuals were followed for three months after leaving their hacking boxes, and
travelled no more than a little over 5km (Powell et al., 2002)).
15
Table 1.1. A summary table of dispersal by peregrines amalgamated from Dennhardt & Wakamiya (2013), Wegner (2017) and additional data from other published papers (indicated in the table).
Area Male peregrines Female peregrines References
Mean Distance (km)
Sample n
Range (km)
Mean Distance (km)
Sample n
Range (km)
Scotland 20 24 10 – 68 68 15 3 – 185 Mearns &
Newton 1984
Scotland and North
England (captured as
breeders)
48 8 0 - 229 80 12 11 - 104 Smith &
McGrady 2009
Scotland and North
England (ringed and
subsequently
recovered dead in
the study area)
326 1 n/a 98 9 9 - 211 Smith &
McGrady 2009
Alaska 69 6 4 – 206 121 20 2 – 370 Ambrose &
Riddle 1988
USA Midwest 174 73 354 67 Tordoff &
Redig 1997
Greenland 28 21 27 6 Restani &
Mattox 2000
Baden-Württemberg
(Germany)
54 110 5 – 350 121 129 10 – 500 Rockenbauch
2002
East Germany 29 56 <5 –
250
118 51 <5 – 400 Kleinstäuber
2006
Sweden 46 30 6 - 206 137 37 13 - 425 Lindberg
2009b
Spain 65 11 3 – 284 109 11 17-357 Zuberogoitia
16
et al., 2009
USA Pennsylvania 161 21 338 24 Katzner et al.
2012
USA Midwest 108 90 Min.
0.19
226 101 Max. 876 Dennhardt &
Wakamiya
2013
Netherlands 57 34 9 – 242 125 38 44 – 379 van Geneijgen
2014
North Rhine-
Westphalia
39 135 0 – 290 111 152 10 – 550 Wegner &
Thomas 2012
Median
distance
(km)
Sample
n
Range
(km)
Median
distance
(km)
Sample
n
Range
(km)
New England 99 93 0 –
3710
202 111 2 – 2102 Faccio et al.,
2013
Sicily 19 6 0 – 250 25 12 0 - 218 Bondì et al.,
2018
South Scotland-
North England
36 21 18 – 57
(IQR)
85 47 31 – 125
(IQR)
Morton et al.,
2018
Across Britain (1964
– 2016)
46 290 26 – 89
(IQR)
76 299 35 – 143
(IQR)
Morton et al.,
2018
IQR = Interquartile Range
17
1.4.2 How does my research add to this?
Research on peregrines in Britain has been relatively limited, with most dispersal analysis based
on peregrines hatched from nests in Scotland and northern England using traditional metal rings
and passive integrated transponder (PIT) tags (Smith & McGrady, 2009). The most recent
detailed analysis by Morton et al. (2018) analysed both data from these areas on a local scale
(1974 – 1982 and 2002 – 2016) and on a regional scale using national data on peregrines ringed
and recaptured or recovered anywhere in the UK, between 1964 and 2016.
Colour ringing studies began to develop during the 2000s including Northern Ireland, Shropshire,
Cornwall, the Midlands and the north-west. Orange colour rings for peregrines are also
dispensed to ringers not part of discrete projects. Despite these efforts nothing has yet been
published in peer-reviewed journals on the recoveries from colour-ringed peregrines and little is
known about the dispersal of peregrines in southern England. Therefore, my research offers the
first insight into where colour-ringed peregrines are dispersing from their nests in southwest
England.
1.5 Replicating my studies
The BTO has the highest standards of ringing in the world. Colour ringing peregrines uses a
standard trained procedure that is used by ringers across the UK. The methods used in this
research are replicable and being used both by other colour ringing groups and members of the
team in other parts of the southwest of England.
18
Chapter 2
Dispersal of peregrines in the southwest of England
2.1 Introduction
2.1.1 Dispersal of peregrines post-fledging
While the dispersal behaviour of peregrines has been studied and published across North
America, parts of Europe and Scotland combined with very northern parts of England, there is
little indication or published research on how peregrines in southern England disperse. While
(Morton et al., 2018) provide results on the dispersal of peregrines both on a local scale, in
Scotland and northern England, and regionally across the UK, there is no indication of how
peregrines in particular other regions of the UK are dispersing. However, they do acknowledge
that examining peregrine dispersal on a local scale can generate very specific patterns that differ
to the UK-wide trend.
2.1.1.1 What do we know?
From these research papers we know that male peregrines protect and maintain territories
which females seek out. Therefore, females disperse further than males, sometimes two or three
times the distances, particularly when their populations are expanding. However, when their
populations stabilise, dispersal distances reduce. While most dispersal studies don’t detect any
preferred direction for travel, some detect biases towards certain directions seeking out new
territories or habitats (Faccio et al., 2013; Morton et al., 2018). Others that don’t detect any
directional bias still find that peregrines seek out locations close to water, for example, the Great
Lakes of North America (Tordoff & Redig, 1997).
19
Morton et al. (2018) detected a northerly bias influenced by male peregrines when studied on a
regional scale. In the Mid-west, USA, peregrines headed in a northwest and southeast direction.
Here they appeared to be dispersing along the Mississippi River and heading into urban locations
close to water (Dennhardt & Wakamiya, 2013). In New England peregrines dispersed in a
southwest direction, limited by the sea on the east and southeast coastline (Faccio et al., 2013).
2.1.2 What gap is there to fill?
There is very little published on how peregrines in southern England are behaving, particularly
from a population and dispersal perspective in modern times since their population recovery.
Wilson et al. (2018) have broadened what we now know about the breeding population of
lowland England. They also highlight many of the threats that peregrines face, particularly in
northern England and Scotland, although other areas, such as the north Cornwall coast are also
affected (Steve Watson pers. comm.). These include habitat degradation, persecution, changing
racing pigeon abundances and racing routes and decline in prey species as well as inter-specific
competition. Additionally, DDT is still affecting the eggs of peregrine populations in Germany and
Greenland through global weather movements moving DDT as aerosol - from parts of Latin
America and Africa - as clouds which precipitate down further north (Wegner & Fürst, 2009; Falk
et al., 2018), while brominated flame retardants (PBDEs) in effluent from the furniture industry
also pose a threat to the health of top predators such as peregrines (Lindberg et al., 2004;
Lindberg, 2009a).
Therefore, the data that I have compiled presents for the first time how peregrines, specifically
on a local scale in the southwest of England, disperse. Gleaning more information about how the
peregrine lives in Britain is a priority because in some parts of their British range they are
declining, particularly in northern England and Scotland. The UK also holds up to 14% of Europe’s
population of peregrines and it is listed on Annex 1 of the EU Birds Directive (Wilson et al., 2018).
Therefore, peregrines dispersing from the southwest of England have a crucial role towards
increasing and establishing new populations in areas where they are absent or present in low
densities.
20
2.1.3 Predictions and expectations
Analysing where lowland peregrines from southwest England disperse provides insights into the
species’ behaviour that address a gap in the wider literature. I predict that peregrines from the
southwest of England show a bias in their direction of dispersal, in particular moving in an east-
north-easterly direction. This is based on many recoveries of individuals coming from the
Midlands, north London and Norfolk. With breeding pairs across southern England high and
thought to be largely saturated, and the coastline around southern England acting a potential
barrier to continue south and southeast, I predict peregrines are heading north and east into
new, unoccupied areas (Wilson et al. 2018).
In addition, I predict that the longest-distant birds will be females because across their range
they travel further than males both during their natal dispersal and when looking for male
territories to breed (Morton et al., 2018)). Meanwhile, males stay closer to where they were
hatched, as illustrated by one bird who has not dispersed any distance during his 13 years of life.
2.2 Methods
2.2.1 Field work and colour-ringing
Between 2007 and 2019 peregrine chicks were ringed by a team of trained ringers (myself,
Hamish Smith, Luke Sutton, Seb Loram and Jason Fathers) at approximately three weeks old. A
standard metal identification ring issued by the BTO was fitted to their right leg; a plastic colour
ring was fitted to their left leg. The rings were pale blue or orange, engraved black with a two-
letter or three alpha-numeral code. Biometrics were taken to assess their sex and to contribute
to a wider database for peregrines.
2.2.1.1 Defining habitats
Habitats were defined by the Corine land cover habitat data (Copernicus 2019) while definitions
of specific nesting habitats were defined as follows:
Natural inland cliff would be more than 2km from the coast and a natural coastal cliff would be
less than 1km from the coast ((Wilson et al., 2018). Urban comprises manmade built structures
21
ranging from a cathedral to an office block. Habitats such as semi-natural grassland and wetland
habitats were defined as other in the analysis.
2.2.2 Study areas
Peregrine nests were chosen that had relatively easy access, such as urban-dwelling nest boxes
or cliff sites that can be safely be accessed by experienced climbers. Nests were visited in the
counties or unitary authorities of Bristol, Bath and North-east Somerset, North Somerset,
Somerset, Gloucestershire, Wiltshire and Devon.
Some young birds were found by members of the public on fledging. They were checked over
and ringed on release where they were found. Some young birds that were not able to be
released or returned to their nest site were ‘hacked’ back to the wild and also colour-ringed and
released in Hampshire. The hacking process requires the young birds to be housed in a cage or
box before the door is eventually opened; the birds then return as and when to a ready food
supply until independence.
2.2.3 Defining recoveries
The team of ringers and myself waited over subsequent months and years for recoveries to be
reported and kept in touch with observers at known breeding locations. Recoveries of live, dead
or injured birds were supplied by members of the public, veterinary surgeons and the Royal
Society for the Prevention of Cruelty to Animals; these have been communicated directly to us
from the observers, the BTO or via the BTO’s/Euring ringing reporting system (www.ring.ac).
Recoveries for this study are defined as birds subsequently found dead or alive (resighting or
injured).
2.2.4 Data handling and analysis
The location details such as GPS coordinates and habitat, and the dates for the origin of a bird
and their subsequent recovery (or multiple recoveries), were set out in a csv file and subjected to
analysis using R version 3.5.1 (R Core Team 2016). Hi-res maps were produced using Maps
(Minka & Deckmyn, 2018) and Mapdata (Becker & Wilks, 2018) and kernels using adehabitatHR
package using the function kernel UD (estimation of kernel home-range) (Calenge, 2006).
22
Bearings and coordinates rose charts were developed using geosphere (Hijmans, 2019a), circular
(Agostinelli & Lund, 2017), raster (Hijmans, 2019b) and rasterVis (Lamigueiro & Hijmans, 2019).
Habitat information was extracted using sf (Pebesma, 2018), rgdal (Bivand et al., 2019), dplyr
(Wickham et al. 2019), tidyr (Wickham & Henry, 2019), gglpot2, Wickham, 2016), adehabitatHS
(Calenge, 2006) and SDMTools (Van Der Wal, 2019). Geographic boundary data was developed
using rgeos (Bivand & Rundel, 2019). Habitat data was extracted from Copernicus Land
Monitoring Service (Copernicus, 2019).
Model validation was carried out by examining graphs of:
1. Normal distribution of residuals
2. Homoscedasticity
3. Leverage
A General Linear Model was used for analysing the effect of sex and distance. Differences
between the duration of subsequent recoveries were compared using the Wilcoxon test. The
Rayleigh test was used to compare bearings within and between male and female peregrines,
specifically for identifying unimodal departures from uniformity. The Mann-Whitney U test was
used to compare the medians of altitude data sets. The Fisher exact test was used to compare
occupancy of habitats at the point of ringing and when recovered at a later date.
Where possible, P-values are quoted to three decimal places expect for the rose diagram
statistics where results are quoted as the output provided by the analysis package in question.
2.3 Results
During the analysis information was gleaned from a combined total of 24 females, 21 males and
one unsexed peregrine. Depending on the analyses, different samples were used, for example,
when analysing dispersal beyond a certain distance and time span, fewer individuals were
included.
2.3.1 Where are young peregrines being recovered?
Figure 2.1 shows the individual journeys made by peregrines (n=46). The mean distance for all
peregrines was 75km and median 46.5km. Males travelled a mean 37km and median 16km from
23
their natal site, with a range from 0km to 272km (n=21). Females travelled a mean 105km and
median 95km with a range from 7km to 355km (n = 24).
7% of recoveries comprising birds ringed as chicks were found over 200km away.
Out of a sample of 46 birds 54% were found within 50Km of the ringing sites, 15%
between 51 and 100km and 24% at 100 – 199km.
24
Figure 2.1. Arrows joining locations of ringing with locations of recovery: blue = location where peregrines were ringed as chicks; red = location where the same peregrines have been recovered.
We can use the observed point sample to estimate the probabilities of recovery in relation to the
analogous distribution for initial ringing locations. This can be done with 2D kernel density
estimates, which can be thought of as a two-dimensional moving average, smoothing over the
point samples. For the analysis a 95% probability was used and therefore, in Figure 2.2, the
kernals represent the minimum area where there is a 95% probability of the peregrines
occurring. This figure also shows that while the density of recoveries (red kernel) overlaps with
where the birds were ringed (blue kernel), there are many birds dispersing further: into other
parts of England, particularly into the Midlands, northern England and some parts of eastern
England.
25
26
Figure 2.2. 95% kernels overlaid on a map of England and Wales: blue = location where peregrines were ringed as chicks; red = location where peregrines have been recovered. Clearly, ringing locations in the sea are impossible, but recoveries could be (death at sea).
Figure 2.3 provides further insight in which sexes are responsible for these differences. There was
a significant difference specifically between male and female peregrines (t = -2.94, df = 40.381, P
= 0.004). The unknown peregrine is likely to have been a female based on the distance it
travelled when compared with the boxplot for male and females.
27
Figure 2.3. Boxplot comparing the distances travelled by known sex birds and unknown: F = female (n=24); M = male (n=21) and U = unknown sex (n=1). Thick horizontal bars are medians, the boxes span the interquartile range, ‘whiskers’ extend to the first point within 1.5 interquartile ranges from the nearest quartile, and circles (lying outside the whiskers) are flagged as potential outliers. However, without independent evidence that the data are unreliable, there is no reason to remove outliers.
As indicated by figure 2.4, there was no significant difference between the periods in which
female and male peregrines were recovered (t = -1.13, df = 43, P = 0.264). Male peregrines were
recovered between 42 days and 2820 days (7 years, 8 months and 3 weeks) of being ringed, with
a mean of 570 days and median 364 days. Females were recovered between 36 days and 2549
days (6 years, 11 months, 3 weeks and 3 days) of being ringed, with a mean of 793 days and
median 607 days.
28
Figure 2.4. Box plot comparing the duration in which peregrines were recovered after being ringed as chicks: F = female (n=24); M = male (n=21) and U = unknown sex (n=1). Boxplot description as in Figure 2.3.
2.3.2 What directions are dispersing peregrines travelling in?
29
Legend
= individual birds
= relative abundance of observations in 10° segments
= mean bearing
= relative distance of dispersal
Figure 2.5. A rose diagram showing the direction of travel for male and female peregrines (n=32), Rayleigh test of deviation from uniformity: Z = 0.47, P<0.001.
Figures 2.5 to 2.7 show that both for both sexes combined, and for females, the direction in
which they are dispersing (north-east) is highly significant. While male peregrines appear to have
a tendency to move north-north-east this orientation is not significantly different from a uniform
distribution (P = 0.093). However, there was no significant difference between the bearings made
by female peregrines and those made by males (Watson’s Two-sample Test of Homogeneity, Test
Statistic: 0.05, df = 31, P > 0.10).
30
Figure 2.6. A rose diagram showing the direction of travel for female peregrines (n=16), Rayleigh test of deviation from uniformity: Z = 0.55, P=0.001.
Figure 2.7. A rose diagram showing the direction of travel for male peregrines (n=15), Rayleigh test of deviation from uniformity: Z = 0.38, P=0.093.
2.3.3 What elevation are peregrine dispersing to?
Ringing sites are primarily at low elevations (Figure 2.9), unlike the range of elevations found
across the UK as a whole (Figure 2.8) (W = 17,306,000, N1 = 46 & N2 = 483,297, P<0.001). The
places where peregrines have been recovered are also mainly low elevation sites below 400m
(Figure 2.10) and differ significantly to the range of elevations shown by the national dataset (W
= 15,230,000, N1 = 483,297 & N2 = 46, P<0.001). There is no significant difference between the
elevations where peregrines are ringed and where they are recovered (W=888.5, N1 = 46 & N2 =
46, P = 0.186).
The maximum elevation at which chicks were ringed was 217m with a median of 37m. The
maximum elevations reached by the sexes when recovered was 270m by a male and 284m by a
female. The median for each sex was 50m and 63m respectively. There were no significant
differences between the elevations where male and female peregrines were ringed (W = 184.5,
N1 = 24 & N2 = 21, P = 0.125), or where they were recovered (W = 238, N1 = 24 & N2 = 21, P =
0.759). There were also no significant differences in the elevation within each sex between their
31
Figure 2.8. Bar chart showing the elevation of 1km squares from across the UK (Source: https://biogeo.ucdavis.edu/data/diva/msk_alt/GBR_msk_alt.zip).
ringing and recovered locations (Male: W = 158, N1 = 24 & N2 = 24, P = 0.118; Female: W = 277,
N1 = 21 & N2 = 21, P = 0.828).
32
Figure 2.9. Bar chart showing the elevation at which peregrines were ringed (n=46).
Figure 2.10. Bar chart showing the elevation at which peregrines were recovered (n=46).
2.3.4 What habitats are peregrines dispersing to?
Out of 20 peregrines recovered after 12 months, 45% (nine individuals) were still found in urban
habitats, 20% (four individuals) were still found at urban cliffs or quarries and one bird (5%) was
found still at a coastal cliff. Three birds (15%) had moved from an inland cliff or quarry to an
urban location, one bird (5%) had moved from an urban location to a coastal cliff, and one bird
(5%) had moved from a coastal cliff to an urban location. There was no significant difference
between the proportion of peregrines using specific nesting habitats when ringed and when
subsequently recovered (Fisher’s Exact Test, P = 0.532, alternative hypothesis two-sided) (Figure
2.11). Eight further individuals after one year were recovered away from specific breeding
habitat in the wider countryside or on wetlands.
Urban Inland cliff/quarry Coastal cliff0
10
20
30
40
50
60
70
50
40
10
65
2015
Habitat where ringed Habitat when re-sighted or recovered
Habitat
% F
requ
ency
Figure 2.11. Bar chart comparing the nesting habitat that peregrines were ringed in and subsequently recovered in after 12 months or more. Peregrines recovered in areas away from immediate nesting habitat were excluded, for example, wetlands. Numbers above each bar represent the actual percentage calculated.
33
There was no significant difference in the distribution of peregrines across different habitats
(Figure 2.12), based on the Corine land cover data set, between the ringing locations and where
they were recovered (Fisher’s Exact Test, P = 0.286, alternative hypothesis two-sided).
Figure 2.12. Bar chart comparing the local habitats were peregrines hatched and where they were recovered based on the Corine land cover data set. Numbers above each bar represent the actual percentage calculated.
2.3.5 Specific Case Studies
Siblings of the same family from one breeding season are sometimes recovered providing
additional insights into where related peregrines from one location disperse to.
2.3.5.1 Avon Gorge
Two siblings ringed on the 21st May 2012 have been identified alive. One, a female ringed DZ, was
found in an agricultural field southeast of the Avon Gorge 63 days later and 16km away. Her
sister, DX, headed north-east into Gloucestershire and was seen on Tewkesbury Abbey. She then
headed into Shropshire where she was observed breeding at an inland quarry.
34
2.3.5.2 Town hall, Bournemouth
All three siblings, HF, PJ and PK, ringed on the 16th May 2017 have identified alive. HF, a male,
headed to the centre of the town of Poole 7km west. PJ, another male was spotted 29km north-
east in semi-rural habitat near Salisbury. PK, a female, has been seen south of Bournemouth
nesting at a cliff site 11km away.
2.3.5.3 Scabbacombe, Devon
Two siblings, both males, were ringed on the 28th May 2017. One, LB, was found dead a year later
still in Devon, 51km away and the other, LC, was found also dead 3km away from where it was
ringed 15 months later.
2.3.6 Additional sightings of interest
2.3.6.1 West Bay, Dorset
A male peregrine, CK, was released back onto the beach after his nest collapsed from the cliffs
after heavy rain. He was spotted alive 272km north at Belper, Derbyshire, a year and a half later,
where he is now the resident breeding male.
2.3.6.2 St John’s Church, Bath
A female peregrine, GA, was ringed on the 29th May 2013. She travelled from Bath to Norwich,
287km to the north-east, just under two years later. Her movement has become well known in
Norwich after the then breeding female disappeared leaving four chicks to be reared by the
breeding male. When the young fledged GA killed or fatally injured them and subsequently
paired up with the male.
2.3.6.3 Halifax
A female peregrine ringed on the 18th May 2013 was found dead at the bottom of an industrial
chimney in Halifax, West Yorkshire, just under two years later. She had travelled 355km, the
furthest of the colour-ringed peregrines in my study.
2.3.6.4 Morocco
A male peregrine ringed on the 30th May 2019 in Taunton, Somerset, was recovered dead in
Tiznit, Morocco on the 1st November 2019. Although not included in the analysis, this bird is the
first British-ringed peregrine to travel to mainland Africa, a total of 2435km. His parents are both-35
colour-ringed. The female originates from Bath, North-east Somerset, and the male from Exeter,
Devon.
Only one other British-ringed peregrine has made it this far, travelling slightly further south to
Lanzarote in the Canary Islands, and two other peregrines have been recovered along the west
coast of Portugal (Robinson et al. 2019).
2.4 Discussion
This study is the first of its kind focusing on the movements of peregrines hatching from nests in
the lowlands of southwest England, which holds the largest regional population of peregrines
with an estimate of 263 pairs (Wilson et al., 2018). It is part of a growing contribution of studies
about peregrine behaviour in the UK, mainly from Scotland and northern England, where
peregrines are largely rural, remote and nesting on natural rocky hillsides and mountains at
higher altitudes. In contrast, this study provides insights into peregrine behaviour in lowland
England that comprises a mix of urban, semi-natural, coastal and agricultural landscapes.
During the past 20 years there has been a growing interest in peregrines in the UK, coinciding
with their increasing populations across the country, particularly in urban areas (Wilson et al.,
2018). In the 1980s, the peregrine was deemed one of the most studied raptor species in the
world, largely due to the extensive research that examined the effects of organophosphate
chemicals and other factors on this species’ breeding success and its migratory behaviour
(Mearns & Newton, 1984; Newton & Mearns, 1988). More recently there have been peer-
reviewed papers examining the breeding populations of peregrines in Wales ((Dixon et al., 2009)
and across the UK (Wilson et al., 2018). Other publications from the UK have mainly focused on
dispersal, survival, breeding success and decline in Scotland and northern England (Hardey et al.,
2003; Smith & McGrady, 2009; Amar et al., 2012; North East Scotland Raptor Study Group, 2015;
Smith et al., 2015; McGrady et al., 2017; Morton et al., 2018). Some researchers, including the
author, have examined peregrine diets in southern and central England ((Dixon & Drewitt, 2008;
Sutton, 2015; Kettel et al., 2016; Dixon & Drewitt, 2018) and how their diet relates to breeding
performance (Kettel et al., 2018; Kettel et al., 2019) and racing pigeons (Dixon, 2002; Parrott et
al., 2008; Dixon et al., 2018).
36
Despite this, little has been published on the movements of peregrines in lowland England, even
though over 400 young have been ringed per summer in recent years (BTO Online Ringing and
Nest Recording Report, 2019). They are one of the most watched raptors in Britain thanks to
their association with cathedrals, churches and high-rise buildings, where web cameras are often
fitted and streamed across the Internet. Much of what is observed remains unpublished in
project blogs or is printed in county bird reports or raptor group reports, which reach out to a
limited, often membership audience, and most are not available online or entered into a search
engine library.
Across Europe, the subspecies of peregrine, F.p.peregrinus, has largely had its population
recovery documented as a published book of papers, ‘Populations, Status and Perspectives in the
21st Century’ by editors Janusz Sielicki and Tadeusz Mizera in 2009, following the second
international peregrine conference in Poland in 2007. After the third conference in Hungary in
2017 papers focusing on the peregrine’s recovery and behaviour were published in a special
edition of Ornis Hungarica in 2018 (volume 26, part 2).
Dispersal studies from Germany reflect the most extensive and detailed research of resident
lowland peregrines that we can compare with in the UK, alongside those from Sweden, although
the latter focus on northern birds that nest at higher latitudes, often on bogs and mires, and with
greater migratory tendencies. (Kleinstäuber et al., 2009; Lindberg, 2009b; Wegner et al., 2009;
Wegner, 2017).
2.4.1 Peregrine dispersal
This study reveals that female peregrines from the southwest and west of England are dispersing
in a northeast direction, either as part of their ongoing juvenile dispersal within their first two
years of life, or while choosing a breeding location. This is different from some studies in the UK
where peregrines did not show a preference for any particular direction ((Mearns & Newton,
1984; Smith & McGrady, 2009) while those studied by Morton et al. (2018) showed a northerly
preference influenced by male birds. With southern, and more recently central parts of England,
already occupied by peregrines, they appear to be exploring and colonising areas further north
and east where there are fewer occupied territories, replicating similar population expansions by
other species such as buzzards and ravens Corvus corax (Balmer et al., 2013; Wilson et al., 2018).
37
For example, based on Wilson et al. (2018), in 2014 estimates of the number of pairs in the more
populated English regions included:
English Region Estimated number of pairs
Southwest 263
Southeast 82
Central 83
West Midlands 104
Pennines 113
While the areas where peregrines, particularly females, in this study are heading include:
English Region Estimated number of pairs
East Anglia 45
Northeast 44
Northwest 61
Female peregrines in this study therefore appear to be travelling into English regions (north and
east) where there are fewer pairs and where they are recovering in places they have not existed
for decades, if not hundreds of years (Wilson et al. 2018; Ratcliffe 1993). Dispersing north and
east also makes sense from a geographical point of view; heading southwest, south and
southeast not only means there are fewer or no vacant territories, there is also the sea which
probably acts as a barrier to birds heading further south and east into France, Belgium and the
Netherlands. Despite this, occasional peregrines from Cornwall have appeared on the French
coastline (Mark Grantham pers. comm.), and the exceptional record of a juvenile peregrine
hatched in Taunton, Somerset in 2019 was recovered dead in Morocco six months later.
The results of dispersal distances differ slightly, depending on the sex of individuals in studies by
Mearns & Newton (1984), Smith & McGrady (2009) and Morton et al. (2018), all of which were
38
conducted in Scotland and northern England. Compared to Mearns & Newton (1984), the median
distances in this study were only 4km less for males and 27km more for females. Mean distances
compared with those by Smith & McGrady (2009) find female peregrines dispersed 25km further
while males dispersed 11km less. Finally, when compared with the most recent paper by Morton
et al. (2018), this study’s results show the median dispersal distance was 10km more for females
and 20km less for males. While comparisons between studies that use mean figures need to be
viewed with some caution, as they do not reveal the overall spread of data and overlap between
sexes and distances, this still reveals an interesting comparison. The low dispersal distance for
male peregrines in this study aligns with findings by Morton et al. (2018) that on a
regional/national scale, male peregrines have reduced their dispersal distance as the peregrine
population has grown and stabilised. Female peregrines are dispersing greater distances than all
three studies, perhaps because many territories in southern England are now occupied and
therefore pushing them further afield to seek unpaired males. In Derek Ratcliffe’s own studies,
he found out of 554 peregrines ringed in Britain and Ireland and subsequently found dead, the
distances travelled differed little between regions with an overall median distance of 45km. He
found 55% had moved less than 50km, 78% less than 100km and 6.7% 200km or more, which
aligns with this study where similar proportions were found (54%, 69% and 7% respectively)
(Ratcliffe, 1993; Wernham et al., 2002).
Morton et al. (2018) have analysed peregrine dispersal in Britain in the greatest detail and
provide insights into what peregrines are doing both on a local scale in southern Scotland and
northern England, and across a regional scale covering the UK. As with other studies, female
peregrines dispersed the furthest as part of female-biased dispersal while the males exhibited
male-biased philopatry. They found that on a local scale the number of male peregrines
dispersing over 100km doubled (from 9% to 20%) when the population had stabilised. The
proportion of the longest-travelled females (>100km) reduced by 10% during the stable phase
(from 52% to 42%). However, on a regional scale across the UK, females reduced their distance
by 7% (56% to 49%) and males reduced their distance by half (30% to 16%) showing that
nationally peregrines have reduced their dispersal distances as their population has increased.
This pattern of reduced dispersal was also observed in the Netherlands and Germany after
peregrine populations had increased (Rockenbauch, 2002; van Geneijgen, 2014; Wegner, 2017).
39
2.4.1.1 Density dependence considerations
One consideration for the behaviour of the peregrines is density dependence, the effects of
which have been assessed by Smith et al. (2015) and Morton et al. (2018,) and vary between
local and regional scales. While it might be assumed that as a population of peregrines in one
area becomes saturated, floating peregrines move into new areas with lower territory
occupation, Morton et al. (2018) have shown this is not always the case. By examining dispersal
distances across three different time periods and at both local and regional scales, they found
that sex alone was the meaningful predictor of dispersal distance for peregrines in southern
Scotland and northern England.
The results from Morton et al. (2018) show how on a local scale peregrine dispersal will differ
from that found on a wider regional/national scale. Such local variability is important to take into
account when examining how peregrines in the UK disperse. While sex may be the important
factor in dispersal, different local populations of peregrines may disperse in slightly different
patterns depending on habitat, interference by man, prey availability, changing climate and
interactions with other peregrines.
Morton et al. (2018) raise a further explanation that such a negative relationship between
dispersal and population increase over time could be due to a mate-finding Allee effect.
However, they discount this on the premise that both male and female peregrines showed
negative density dependence and not just females, who are the sex that select mates.
In contrast, Smith et al. (2015) found that on a local scale dispersal is density dependent, causing
juvenile peregrines to disperse further from where they hatched. This was related to a high
density of peregrines and occupied local territories in their natal area. With fewer sites available
young birds move further afield to look for vacant sites. However, some caution has to be noted
as the methodology involved looking at whether peregrines were re-encountered inside or
outside their study area using re-capture techniques and PIT tags at nest sites, rather than
distances moved from a to b through traditional resightings of live birds or recoveries of dead or
injured ringed/colour-ringed birds.
In summary, from the most recent papers by Morton et al. (2018), McGrady et al. (2017), Smith
et al. (2015) and Smith & McGrady (2009), sex is the overall determining factor that influences
the dispersal distances of peregrines. However, population density does have some effect on
40
peregrine dispersal, although this may vary under different situations. There is evidence that as
population density increases, first-year peregrines may disperse further. However, at a certain
point, a higher density of peregrines becomes more widespread and this dispersal behaviour
becomes more risky than leaving their familiar natal area.
2.4.1.2 Floaters
Floaters are those peregrines which are non-breeding and/or non-territorial and are more
apparent in saturated populations waiting for territories to become available (Kauffman et al.,
2004; Morton et al., 2018). Volunteers who watch peregrine nest locations, such as the Avon
Gorge, Bristol or Yat Rock, Gloucestershire, frequently comment on encounters between the
local breeding pair and other peregrines or floaters overhead, with the territorial pairs chasing
off the intruders or floaters (Steve Watson pers. comm.). Observations at breeding locations are
revealing rival male and female peregrines hanging out at the nest sites early in the nesting
season waiting for their own opportunity to breed. Fighting may pursue, often with males
targeting males and vice versa (pers. comm. Steve Watson). During a peregrine’s lifetime
peregrines will breed with several mates, sometimes up to five (Lindberg, 2009a). Males take up
the higher quality nesting locations first, followed by lower quality sites. It appears that despite
increasing peregrine densities, nest locations that have had breeding success get used in
following breeding years, while sites with no breeding success are often abandoned (Smith et al.
2015).
When adult paired birds suddenly disappear from the breeding location, often presumed or
found dead, they appear to be replaced very quickly by floaters. For example, the colour-ringed
peregrine, with ring letters CK, was released near to where its nest collapsed in Lyme Bay, Dorset
as a juvenile bird. Two years later CK was found in Belper, Derbyshire, 275km north-east, where
he paired up with a female peregrine. She had just lost her partner two days previously and he
was found dead nearby.
In my study, many of the peregrines recovered away from specific nesting locations or nesting
habitat may have been floaters. Morton et al. (2018) discusses that recoveries of peregrines, in
this case those not recaptured or resighted alive birds at nests, are most likely to be floaters, and
strongly influence negative density dependence. This is because floaters may stay closer to their
familiar natal area, ready to take up a new territory that becomes available or oust an individual
41
off his or her territory. Equally, they may travel further afield, as GA, a female colour-ringed
peregrine did by travelling from Bath to Norwich in her first year. She then fought with the
breeding female, who had young, and subsequently disappeared. As the young fledged GA then
killed or injured them one by one, pairing up with the breeding male once they were all dead and
attempting to breed with him in the following year. The long distance travelled by a young
peregrine to Morocco suggests this bird was moving to northern Africa for the winter; had it not
died the bird is likely to have returned back to England or western Europe. His movements
replicate those of northern European peregrines that breed in Scandinavia, for example Finland,
and winter in southern Europe, with some making it to Morocco and Algeria (Tuomo Ollila pers.
comm. 2009).
2.4.1.3 Cooperative Breeding
A new phenomenon that appears to be happening as a result of increasing or stable peregrine
populations is cooperative breeding through the presence of single, related, one-year-old male
birds. On occasions where these young birds are already colour-ringed, it has been shown that
they hatched from the exact nesting location the year before. They are staying with their parents
the following year after fledging and becoming a helper bird, apparently honing their hunting
skills and obtaining ‘free’ food often by begging like recently fledged chicks (pers. obs.). This
behaviour has been reported in London (2018), Bath (2012 & 2017), Brighton (2005), South
Gloucestershire and Cumbria, often with known colour-ringed birds. Further afield it has been
well documented in Germany (both recently and since the 1930s), France, and in small numbers
in Italy, Australia, Canada and Japan (Kurosawa & Kurosawa, 2003; Drewitt, 2014). These ‘helper’
birds are mainly male, while the females get chased off and naturally disperse further away
seeking unpaired (or sometimes paired) males. In west Germany, Peter Wegner has observed
this behaviour happening on at least nine nests in his study area (Wegner & Thomas, 2012). He
explains how female peregrines often attempt nesting in their first spring, although they often lay
later in the season and less successfully than more experienced females. In stable, fully occupied
areas Wegner and Thomas find only 3% of 1st-year females may attempt to breed while in
recovering areas this increases to 20%. Meanwhile, first-year male peregrines rarely attempt to
breed and when there are fewer available territories, it is likely they will become helper birds or
simply wander as floating birds (Wegner 2017).
42
The appearance of some helper birds and cooperative breeding in parts of the southwest and
southeast suggest that for some male birds, particularly in their first few years, there is a greater
advantage of staying in their natal area with their parents.
2.4.1.4 Specific nesting habitats
Of the peregrines analysed (n=20), just under half of individuals remained in urban locations
while a fifth remained at inland cliffs or quarries. The rest in this particular analysis were found at
coastal cliffs and in semi-natural habitats, in particular wetlands. With 65% of peregrine being
recovered in urban locations, there appears to be a shift, albeit an insignificant one, of peregrines
moving into towns and cities.
The relatively small sample size accounts for what seems like large shifts in peregrines moving
between an urban environment and a non-urban environment. However, in reality this only
relates to three or four birds. For example, while 20% of peregrines moved to an urban
environment from a non-urban environment, this only comprises four individual peregrines.
These results differ from eastern Germany where 95% of peregrines that fledged on cliffs
returned to breed on them, while 81% chicks that fledged from buildings later returned to nest
on them (Kleinstäuber et al., 2018). Here, distinguishing between the different types of habitats
used by peregrines reveals the separate sub-populations of peregrines which are attracted to
particular habitats and to which they remain faithful to throughout their lifetime (Sömmer &
Kirmse, 2013). Peregrines are attracted to cliffs and buildings with equal attraction in Germany
and it is likely floaters will breed in the same habitat that they fledged from (Kleinstäuber et al.,
2018). For example, in eastern Germany we see a restricted exchange between cliff and building
nest sites: 4% moved from buildings to cliffs and 6% moved from cliffs to buildings. There were
also exchanges between tree-nesting birds with 35% moving from trees to buildings, 5% from
trees to cliffs and virtually none moving from cliffs or buildings to trees (Kleinstäuber et al., 2009;
Kleinstäuber et al., 2018). Their 2018 study, which builds on their work published in 2009, has
since split the category for buildings into two, with structures such as pylons,
telecommunications towers and cranes forming a new category ‘lattice structures.’ Their reveal
that 62% of peregrines using lattice structures originate from tree nests, 17% from buildings and
11% from cliffs. From a conservation perspective, understanding what proportion of peregrines
switch between nesting habitats, and how peregrines disperse, can help peregrine scientists
43
better support the recovery of tree-nesting peregrines which almost disappeared during the
DDT-era. In Germany just under half (43%) of tree-reared peregrines leave to breed on buildings,
cliffs and lattice-structures, and most of these are females. Critical to the tree population’s
recovery are the male birds which don’t disperse very far; if they hatch in a tree nest 90% of
them will remain faithful to tree nest sites. Furthermore, 95% of tree nesters originate from tree
nests. If their population continues to recover and the density of tree-nesting peregrines
increases then it is likely more peregrines from tree-nests will pair up and breed. In summary,
tree-nesting peregrines are recruited from within their own ‘isolated’ population (Kleinstäuber et
al., 2018).
In my study, after one year, eight peregrines were subsequently found away from typical
breeding locations such as urban locations and cliffs. They were instead discovered on wetlands
and semi-natural habitats and were probably wintering or non-breeding birds (floaters), or
breeding birds hunting away from their immediate nesting locations. Across open agricultural
land peregrines will nest on pylons and it is possible some recoveries were of pylon-nesting birds
situated amongst semi-natural, agricultural or wetland habitats.
Given time, these floaters that appear to still be dispersing, may well appear back in urban and
cliff habitats in future years when they are at breeding age. For example, in Sweden, female
peregrines first breed when they are 1.93 years old (in their 2nd calendar year) and males at 2.65
years old (in their 3rd calendar year) (Lindberg, 2009a). The analysis for this part of my study
looked at recoveries of birds after 12 months of fledging to include a large enough sample.
However, recoveries after 24 - 36 months would give a better indication of where birds settle to
breed and what habitat they use as this is when they are more likely to be nesting. In areas of
lower density, first year-female peregrines may attempt to breed in larger numbers, while in
areas of high density, older and more experienced females are in greater abundance meaning
there are fewer opportunities for first-year females to attempt nesting (Wegner, 2017).
The lower occurrence of sightings or recoveries of peregrines at inland cliffs or quarries may be
down to the nature of quarries which are often inaccessible and remote. Even if ringed
peregrines are found in a quarry, they can be at such a distance where their rings cannot be read.
44
2.4.2 Why is this latest research on peregrines important?
As with any species of organism, describing how peregrines use their environment is an
important tool in assessing what peregrines may do next; in particular how their success in
southern England may help them to infiltrate other parts of Britain. The more we know about
how peregrines behave and use their environment, the more can be done to protect them,
provide robust science and dispel harmful myths.
As peregrines head north and east, they may be encountering vacant territories. For some this
may be to their demise, as many large open areas of moorland and upland habitats are prone to
illegal persecution, declining prey species such as lapwing, golden plover, meadow pipit Anthus
pratensis and skylark and changing climatic conditions. As a result, some areas may be sinks for
peregrines where they simply disappear (Wilson et al. 2018).
At a time when peregrines are showing declines in some parts of their British range the results of
this study provide an indication of where new peregrines may appear from to recolonise in the
future. There are also many urban peregrines north of the Midlands, for example in Manchester,
Sheffield, Leeds and Wakefield, which are now in places to help with this process; some of these
may have originally come from this southwest population. Southwest peregrines heading north
may also encounter peregrines heading south from southern Scotland and northern England,
with mixing of the two populations and a healthy flow of genes.
While peregrines are pan-global and found in a huge range of environments, there is still much to
learn about their lives in Britain. In England particularly, they remain at their highest population
levels in recent times, and there are greater opportunities for studying them in larger numbers
across a wider area of the country compared to 50 years ago.
2.4.3 Biases or limitations
During my studies there are a number of observer biases or limitations that may limit the
assumptions we make about their wider population.
2.4.3.1 Natal dispersal data vs general dispersal data
There are a range of ways of examining dispersal data, for example, focusing on natal dispersal
and where these birds then settle to breed, as shown in studies in northern Britain and Germany
45
(Mearns & Newton, 1984; Smith & McGrady, 2009; Morton et al., 2018; Wegner, 2017). While in
Sicily, Bondi et al. (2018) has tracked GPS-tagged birds and examined natal dispersal by splitting
their data into a post-fledging dependence period, wandering and wintering periods. For my
study the recovered peregrines included individuals both at breeding sites and those dispersing,
wandering or wintering. This was largely due to an interest in where peregrines are generally
dispersing from southwest England rather than true natal dispersal which examines where they
are found once they begin breeding.
2.4.3.2 Nest locations
The nest sites that we choose are those which are easier to access; we are not accessing sites
based on a random distribution. Therefore, it is possible that the young we are ringing move in a
particular way related to the geography of their locality. The population density of peregrines
may also be different from that found in areas where other nest sites are located. Despite this
limitation we attempt to ring chicks at a range of sites and habitats including urban locations
(both inner city and small towns), occasional industrial sites, quarries (usually on the edge of
villages and towns), coastal cliffs and other cliff sites close to urban conurbations such as the
Avon Gorge, Bristol.
2.4.3.3 Recoveries and observations
The subsequent observations and recoveries of injured or dead birds are found close to where
people are living, wildlife watching and walking, for example, areas close to urban settlements,
public footpaths, nature reserves or fields where farmers are working regularly. The results show
an obvious gap in south Wales. Here there are vast areas of open countryside, hills and
mountains where there is a lower density of people and less likelihood of a peregrine being
found; those in flight or perched might be too far away to be identified and injured or dead birds
may go unseen. Recently a blue-ringed peregrine was reported from a nest in a rural location in
south Wales from several years ago, although the ring letters were unable to be read. This would
have been from the ringing project and suggests peregrines are dispersing there.
With the advent of digital cameras there are now many people, particularly birders, outdoors
with a camera and a long lens at hand now providing many images of peregrines in flight. Often
peregrines are photographed without knowing that they have a colour ring. There will be bias
towards those locations where people with these cameras are exploring; in other areas
46
peregrines may be seen with colour rings and never get photographed or sighted close enough
for the rings to be read, while others may never get sighted at all.
2.4.3.4 Reliance on other people
Throughout the past 12 years upon which my study depends there has been a reliance on other
people reporting sightings of peregrines; there will be some colour-ringed peregrines that get
seen or found, and yet are never reported. Although reliable urban sites, particularly those with
web cameras, can be monitored for colour-ringed birds, it has not been possible to actively go
searching for colour-ringed peregrines across England. Therefore, many peregrines may go
unsighted. Wildlife centres provide recoveries of birds either when chicks fledge early and get
taken into care for a few nights, or birds come in injured and need care or to be euthanised.
Again, these recoveries are of birds that just happen to be found by members of the public.
Many others may go unrecovered, particularly if they are injured or die in a remote area, where
there is cover such as a field of crops, or decompose quickly, for example during the summer,
and become less obvious.
2.4.3.5 Handling chicks
An unknown factor is whether the handling of chicks affects their behaviour or survival and
whether unhandled chicks show any differences in their dispersal. While fledging survival rates
can be assessed, knowing the longer-term survival of unhandled chicks is impossible unless
individuals have particular unique features.
2.4.3.6 Fitness of birds
Another unknown factor is whether the colour rings on peregrines affect their perceived fitness
and mate choice. From a health perspective rings are a safe and a widespread method of marking
birds; their weight is negligent. However, once adult at around two years of age, peregrines have
bright yellow tarsi and talons. Blue colour rings and shiny metal rings mask some of the yellow
skin when fitted and could affect how they are perceived by other peregrines.
2.4.3.7 Rehabilitated birds
Although the majority of young birds in this study were ringed at the nest, a few were ringed
when grounded after fledging. One individual was taken into care after its cliff nest collapsed
before being released the following week. Occasionally young peregrines end up in care
47
overnight before being released the next day. Any birds that were taken into care and hacked (a
soft release method) back into the wild were removed from the analysis. Intervention and
rehabilitation may have an effect on a bird’s behaviour once in the wild and therefore their
dispersal may not provide a true representation of what this species does.
2.4.4 Next steps
There are several ways of taking this forward. The first would be to analyse a wider set of data
from other colour ringing and general ringing recoveries from across the country such as
Shropshire, Cornwall, East and West Sussex and the Midlands to see whether different patterns
of dispersal are emerging on a local scale in these regions. There is also the opportunity to
analyse in more detail whether peregrines are dispersing into areas of low or high peregrine
occupation using the BTO’s Bird Atlas data which is now publicly available. This would also help
to examine cooperative breeding in more detail, how prevalent this behaviour is and how it
relates to population change and dispersal.
Additionally, with more time, analysis could be conducted solely on breeding birds with a known
origin to look at natal dispersal in its purest form without floaters and non-breeders included.
This would give insights into where individuals originated and more clarification on how habitat
faithful they are when it comes to nesting and where their young then nest.
48
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