Biological Conservation 67 (1994) 111-118

CONSERVATION OF THE NATTERJACK TOAD Bufo calamita IN BRITAIN OVER THE PERIOD

1970-1990 IN RELATION TO SITE PROTECTION A N D OTHER FACTORS

Brian Banks English Nature, South East Region, Countryside Management Centre, Coldharbour Farm, Wye,

Ashjbrd, Kent, UK, TN25 5DB

Trevor J. C. Beebee* School of Biology, University of Sussex, Falmer, Brighton, UK, BN1 9QG

&

Arnold S. Cooke

Science Directorate, English Nature, Northminster House, Peterborough, UK, PE1 1UA

(Received 12 September 1992; revised version received 25 March 1993; accepted 1 April 1993)

Abstract The number of known sites (populations) documented by conservationists for the natterjack toad Bufo calamita between 1970 and 1990 in Britain rose from 21 to 40, excluding those resulting from translocations. The progressive reduction in rate of discovery of undocu- mented sites suggests that few further populations will be located. The real overall number of natterjack sites has probably changed little over this period, with successful translocations approximately compensating for the few (three to five) concurrent extinctions. More than 90% of natterjacks in Britain now live in the vicinity of just five river estuaries. Habitat protection, mainly the result of scheduling land as Sites of Special Scientific Interest (SSSI), has been increasingly effective in safeguarding natterjacks, the proportion of safeguarded sites rising .from 60% in 1970 to 83% by 1990. However, the legisla- tion for species protection has proved much less effective. Much of the recent damage on unscheduled sites was a result of agricultural improvements by landowners tgnorant of the presence of natterjacks on their land. The breeding records from natterjack sites are used to examine the possible impacts of radioactivity and climate change, against which site protection alone is no safe- guard. Recommendations are made for conserving natter- )ack populations in the future.

Keywords: Britain, natterjack toad, conservation, radio- activity, climate.

* To whom correspondence should be addressed.

Biological Conservation 0006-3207/94/$07.00 © 1994 Elsevier Science Ltd, England. Printed in Great Britain

lll

INTRODUCTION

It has always proved difficult to ensure a satisfactory balance between the adequate protection of wildlife and habitats and economic pressure to use such sites for other, potentially damaging activities. Central to such arguments is the need to monitor the effects of wildlife conservation legislation to determine how far it succeeds in its stated objectives. The natterjack toad Bufo calamita declined sharply in Britain during the early part of the 20th century, disappearing from more than 70% of its previous localities (Beebee, 1976, 1977), and was first protected by British law under the Con- servation of Wild Creatures and Wild Plants Act of 1975. This protection was subsumed within the Wildlife and Countryside Act 1981 where the species is listed on Schedule 5 (protected animals). The Act upgraded the status of Sites of Special Scientific Interest (SSSIs), and enabled the Nature Conservancy Council to prevent damaging activities from taking place on such sites. Interest in natterjack toad conservation in Britain intensified substantially after about 1970, and the data obtained since that time, formally compiled into a National Site Register (Beebee, 1989), form a basis upon which the subsequent protective legislation can be evaluated. In this paper we analyse observations primarily made over the period 1970-1990 to assess the recent history of this particular protected species in Britain.

Site protection cannot, however, guarantee the survival of natterjack populations. We have examined the effects of two external influences over which conser- vationists have no control, environmental radioactivity

112 B. Banks, T. J. C Beebee, A. S. Cooke

and climate change. The nuclear reprocessing plant at Sellafield on the Cumbrian coast has for several decades discharged liquid effluent into the Irish Sea, leading to contamination of the marine environment, especially close to Sellafield (Hunt, 1989) as well as coastal sediments in north-west England (Woodhead, 1986; Lowe, 1991). Adult natterjacks in some colonies may live in contact with contaminated sediments over a number of years. Climate change could also have pro- found effects for British wildlife including amphibians (Department of the Environment, 1991). In order to help predict effects in the future, timing and success of breeding have been examined in relation to tempera- ture and rainfall respectively.

METHODS

Detecting and monitoring natterjack toad populations A number of organisations including the British Her- petological Society, County Naturalists Trusts and the former Nature Conservancy Council organised surveys aimed at finding sites sustaining natterjack toad popu- lations during the past 20 years and these efforts were supplemented by those of several individual recorders. Mostly the work involved visiting suitable habitats during the breeding season to search for adults, spawn or tadpoles. Reports of new sites were subsequently investigated more thoroughly to establish precise breeding sites and approximate population sizes. The numbers of spawn strings were counted to give esti- mates of female numbers (Beebee, 1977), since females rarely deposit more than one string per year and usually lay them separate from others in shallow water where they are easy to find. Total population estimates were made by doubling spawn-string numbers, since there are generally about equal numbers of both sexes (Denton & Beebee, 1993). Populations were divided into three classes: I, large (100s to 1000s of adults); II, intermediate (high 10s to low 100s); and III, small (just 10s of animals), all as judged by counts of spawn strings averaged over several years. In addition, sites were monitored to determine whether breeding was successful as judged by the emergence of toadlets each year. Breeding success (M) was scored as: 0, failure; 1, few toadlets produced (10s); 2, moderate numbers of toadlets (at least 100s); 3, large numbers of toadlets (usually 1000s). Simple arithmetic means were calculated for all sites to derive measures of breeding success.

Evaluation of species and habitat protection For every natterjack site, information was obtained on habitat status (National Nature Reserve (NNR), SSSI or unprotected), threats and extent of loss or damage from the English and Scottish regional offices of the former Nature Conservancy Council (now English Nature and Scottish Natural Heritage).

Radioactivity estimations Radionuclides were determined in samples of 5-10

natterjacks found dead at three sites in north-west England, including two within 10 km of the reprocess- ing plant at Sellafield. Samples were pooled for each site, weighed, and then ashed in a muffle furnace at 500°C. Ash samples were homogenised and counted on hyperpure germanium detectors with a measurement range of 50-2000 KeV. After gamma counting, duplicate subsamples were dissolved in HF and HNO3, plutonium (Pu) isotopes were separated by the use of ion-exchange techniques and quantified by alpha spec- trometry.

Meteorological data Both temperature and rainfall data were obtained from the recording station at the Institute of Terrestrial Ecology, Monks Wood, central England. Data from this site were used to indicate relative changes in tem- perature or rainfall. Monks Wood is within the polygon formed by extant sites in southern and eastern England and the west coast from the Wirral to the Solway. It is within 30 km of several natterjack popula- tions, including two recently extinct ones and a successful translocation. Where local observations have been made of water tables and/or weather conditions at natterjack sites, these have generally been consistent with data from Monks Wood.

RESULTS

Numbers and sizes of natterjack toad populations The status of Bufo calamita in Britain in 1989 is sum- marised in Table 1, showing a total (including transloca- tions) of 47 extant populations. Sites were subdivided for convenience into four geographical zones, all within the distribution of this species mapped previously (Beebee, 1977). Although sites were usually distinct, in that movement of individuals between them was con- sidered unlikely on the basis of distance or unsuitable intervening habitat, this was not invariably the case and we estimate that there could be as few as 28 truly isolated extant populations including recent transloca- tions (see below). However, this study is based on sites as defined in the National Site Register (Beebee, 1989), which gives a total of 47 (shown in Table 1). The modern distribution of the natterjack in Britain is very much centred on the Irish Sea coast, and in particular

Table 1. Natterjack toad populations known in 1989

Region Number of sites Total

Class

I II III

SE/Midlands (A) 0 1 4 5 Eastern England (B) 1 2 5 8 Southern Irish Sea coast (C) 3 2 2 7 Northern Irish Sea coast (D) 8 10 9 27 Total 12 15 20 47

These data include all translocations and omit two definite extinctions since 1970.

Conservation of natterjack toad 113

Table 2. Natterjack populations associated with estuaries

Estuary Number of Percentage of total populations UK natterjack population

Solway 5 11-23 Esk 2 22 Duddon 9 18-24 Morecambe 1 Up to 0.3 ~ Ribble 2 12-23 AIt 2 18 Dee 1 < 1 Humber 1 <0.5 North Norfolk 1 <0-5 b

Possibly extinct. Translocation.

Ranges reflect error limit estimates of populations sizes.

it was notable that >90% of surviving animals occur on just five estuaries (those of the rivers Alt, Duddon, Esk, Ribble and Solway) as defined by Davidson et al. (1991) and as shown in Table 2.

The number of known natterjack populations in Britain (excluding translocations) doubled between 1970 and 1989, from 21 to 42 (Fig. 1), including two localities in which the toads became extinct over the same period. Thus by 1989 there were 40 extant native populations and seven translocations, giving the total of 47 shown in Table 1. However, all the newly found colonies were within the regions known to contain natterjacks in 1970, so there was no significant range extension, and almost all colonies were in a single county (Cumbria) Also, most of the recently discovered natterjack populations were small; thus by 1974 75% of Class I, 79% of Class II but only 36% of Class III pop- ulations were already known and probably very few populations are still unrecorded.

Table 3 summarises the flux of extinctions and translocations during the past 20 years. Since certainty of the former and success of the latter require observa-

50 A

40

o 30 v

I-- 20

6 Z

I0

,,~,,,.&--,=-"&--'=

av...A ---~

0 I I I I I

1970 1 9 7 4 1978 1982 1986 1990

YEAR Fig. 1. Numbers of natterjack toad sites in Britain. Numbers of known sites in the whole country (A) and excluding Cumbria (ll), omitting translocation experiments but in- cluding the two sites where natterjacks have definitely become

extinct since 1970.

Table 3. Extinctions and translocations of natterjack popula- tions

Period Extinctions Translocations Net Change

n Area Size n Area Success class

1970-74 1 B ?III 3 A 0 1975-79 1 D ?III 2 A,C 0 1980-84 0 - - - - 3 A(1)B(2) 3 1985-89 13 BCD all lII 4 A(3)B(1) 1(+?)

Total 3-5 12 4+

-1 -1 +3 ?

9

n, Number of sites involved. Areas A, B, C and D are as defined in Table 1.

tions over several years to establish, data for the most recent periods were inevitably incomplete. Two small sites were certainly lost in the 1970s, the consequences of breeding site deterioration (drainage and/or acidifi- cation) and (probably) the expansion of a gull colony, respectively; and several more were seriously reduced in the late 1980s, as a result of urban development, terres- trial and breeding habitat deterioration (scrub en- croachment and changed tidal inundation patterns following the construction of a new sea wall). All of these extinctions were of small geographically isolated populations of natterjacks. The earliest translocation efforts in the 1970s were unsuccessful, but since 1980 at least some appear to have established new and thriving populations. Overall, generation of new colonies seems to have approximately counterbalanced recent extinc- tions but numbers of both were small relative to the total numbers of extant sites.

Conservation of natterjacks since 1970 Many of the surviving natterjack populations have been threatened and some damaged or destroyed, dur- ing the past 20 years. Table 4 shows the outcome of threats to natterjack sites, subdivided into four five- year periods. Site numbers (n) in this table refer to known numbers of native (not translocated) popula-

Table 4. Success and failure in the defence of natterjack toad sites from damaging activities

Period Site status Total

SSSI or Wider reserve countryside

n SD U D D n SD UD D n SD UD D

1970-74 16 0 2 0 11 1 4 0 27 1 6 0 1975-79 22 1.5 0.5 1 11 0 3 0 33 1 4 1 1980-84 25 3 1 3 11 0 9 2 36 3 10 5 1985-89 33 10 0 4 7 2 7 2 40 12 7 6

n, Number of sites extant in each category at the end of each 5-year period (excluding translocations). Situations resulting in partial failure were attributed 0.5 to SD (Successfully defended) and UD (Unsuccessfully defended). D, Numbers of sites at which habitat degradation, mainly as a result of scrub encroachment, was a serious problem.

114 B. Banks, T. J. C. Beebee, .4. S. Cooke

Table 5. Analysis of factors damaging natter]ack sites

Period Site status

SSSI or reserve Wider countryside

Planning Agricultural Planning Agricultural Application Development Application Development

SD UD SD UD SD UD SD UD

1970-74 0 2 0 0 1 4 0 0 1975-79 0.5 1.5 0 0 0 2 0 1 1980-84 0 0 2 0 1 3 0 4* 1985-89 5 0 2 0 1 1 0 6*

SD and UD are as defined in Table 4. Totals are different because not all factors were classifiable as planning or agricultural-based. *, in at least eight of these 10 instances the landowners were unaware of the presence of natterjacks when the damage was done.

tions in each five-year period; the maximum of 40 (1985-89) thus takes account of the two extinctions during the 1970s. Categorisation as 'Unsuccessfully de- fended' did not necessarily mean that the site was lost, or even damaged, but only that a planning decision re- lating to it was against the conservation interest. These data indicate that sites with SSSI or N N R status fared much better than those without a statutory level of habitat protection; this was true before the Wildlife and Countryside Act, but has become even more marked since, when the increased numbers of threats (i.e. the successful defences) are taken into account. Thus, before 1980 less than 40% of threats to SSSIs were successfully defended but the proport ion has since risen to 100%.

By contrast, there has been no improvement in the much worse record for sites not on SSSIs. Here the success rate has varied but has always remained below 25%, indicating that despite legislation designed specifi- cally for species protection there has been no detectable benefit for natterjacks. In absolute rather than percent- age terms, instances of lost cases on unprotected sites continued to increase through the 1980s. Fortunately, the proport ion of natterjack sites enjoying statutory protection increased progressively from 60% of known sites in the early 1970s to 83% of those known in 1989. However, a further problem was evident when site deterioration as a result of inadequate management

Table 6. Monitoring of natterjack sites

Region % of known sites at which metamorphosis monitored

(average over period)

1970-74 1975 79 1980-84 1985-89

SE/Midlands 50 100 90 83 Eastern England 59 75 85 90 South Irish Sea 44 74 83 86 North Irish Sea 17 32 63 50

Overall 34 51 73 70

Averages are corrected for changes in known numbers of sites between 1970 and 1989, including extinctions and transloca- tions.

was taken into account. Habi tat degradation sufficient to cause natterjack declines featured as an increasing problem during the 1980s, mainly the result of scrub invasion on heaths and dunes, and by this criterion SSSIs fared no better than the wider countryside.

A further analysis of damage to natterjack sites is summarised in Table 5. Most potentially damaging activities involved direct development (for example, caravan parks or holiday camps) requiring planning permissions, or intensification of agriculture. Whereas successful defence against the former has increased everywhere since 1981, damage from the latter was responsible for most of the recent problems at sites in the wider countryside. These problems in turn arose most frequently in places where the landowners were unaware of the presence of the endangered species, and in some instances would probably have been averted if this knowledge had been available to them.

Monitoring natterjack sites in relation to environmental factors

The impact of radioactivity on breeding success As well as mapping and quantifying natterjack popula- tions, increasing efforts have been expended to monitor breeding success as judged by metamorphosis of toadlets each year. More than 50% of sites in every region were regularly monitored in this way by the 1980s (Table 6). Table 7 shows the reproductive success of natterjack populations living at various distances from the nuclear reprocessing plant at Sellafield, Cumbria, and also at different times relating to the Chernobyl incident of late April 1986. Evidently there were no systematic differences in breeding success between populations near to or far from Sellafield; and the only significant difference with respect to the Chernobyl incident was that populations living near Sellafield did better that year than in those before or after (by t-test, p < 0.05).

Although there was no evidence of breeding impair- ment by radionuclide pollution, the effects of Sellafield and Chernobyl were detectable as isotope fingerprints in natterjack carcasses (Table 8). The ratios of pluto- nium (Pu) isotopes characteristic of Sellafield emissions (Hetherington & Jefferies, 1974) were clearly evident in

Table 7. Breeding success in relation to Sellafield and the time of the Chernobyl incident (April 1986)

Distance of Mean breeding score (M) population

from n 1979-1985 n 1986 n 1987-1989 Sellafield

<50 km 11 1.8(0.3) 8 2.6(0.2)a 9 2.0(0.2)b >50 km 6 2.1(0.3) 6 1-8(0-6) 7 1-9(0-5)

Mean breeding scores (M) were calculated as described in Methods. n, Number of populations used for each estimation. Standard errors are given in parentheses. a, Significantly different from 1979 1985, t = 2.59, p < 0.05; b, Significantly different from 1986, t = 2-25, p < 0-05.

Conservation of natterjack toad

Table 8. Concentrations of selected gamma- and alpha-emitting radionuclides in natterjacks found dead at three sites

115

Site Distance Date n f rom

Sellafield

Radionuclide concentration (Bq/kg wet weight)

Cs134 Cs137 Rul03 Pu239/240 Pu238

Ainsdale 103 km April 1985 10 0-13 7.6 ND <0.005 <0.005 Ravenglass 8 km April 1986 I 0 2-70 12.1 17-2 0.28 0.067 Sellafield <1 km May 1986 5 90-90 320-0 453.0 0.41 0.085

Radioactivity was estimated as described in Methods. ND, Not detectable.

animals living within 10 km of the plant, and absolute amounts of several radioisotopes were higher in these carcasses (taken in April 1986) than those taken from >100 km away in April 1985 (all before the Chernobyl incident). Caesium (Cs)-137 dissolves in seawater and is known to travel further than Pu (Baxter et al., 1979) and this too was reflected by its occurrence (unlike Pu) in carcasses from the more distant site. The third sample, of toads found in May 1986 three days after depositions from the Chernobyl accident, contained the Cs-134:Cs-137 ratio and a high rutherium (Ru) level diagnostic of that emission (Smith & Clarke, 1989). Pu, although present in the Chernobyl emission, was emitted in a particulate form that settled out rapidly and did not reach Britain. Although radio- nuclide fingerprints were clear in these natterjacks, the absolute levels were much lower than those likely to have physiological effects on living animals (Kennedy et al., 1990).

Influence of climate Natterjacks are at the edge of their biogeographical range in Britain, and the onset of the breeding season here varies as a function of both latitude and longitude (Beebee, 1985; Cooke, 1985). Figure 2 illustrates that differences between sites can be substantial. At Formby, one of the 'earliest' sites situated on the South

150

Z 138

126 I-- f./) • •

114 v V.

LL. 0 >- 102

- \ J a

90 I I I I I I I I I I I

78 79 80 81 82 83 84 85 86 87 88 89 90

YEAR 119-1 Fig. 2. Variation in the start of breeding activity. Days of year on which spawn was first observed at Caerlaverock (ll), Formby (A) and Woolmer (V) over the period for which

information was available from all three localities.

Irish Sea coast, spawning between 1979 and 1990 some- times began as early as Day 90 (31 March in a non-leap year) and never started later than Day 119 (19 April). Caerlaverock, the most northerly British natterjack site, had start dates ranging between 10 April and 19 May, while Woolmer, an inland site in southern England, was intermediate. Starting dates at Caerlaverock were significantly later than at Formby (t22 -- 4.59, p < 0-001) or Woolmer (t22 -- 3.73, p < 0.01). It is likely that these differences stemmed from differences in both spring temperatures and in rainfall patterns at the various sites. These aspects of climate can be difficult to distin- guish; as shown in Table 9, only at Formby was there a significant trend for breeding to start earlier in warm springs, and this general lack of significance was probably because warm springs were often also the driest. Rainfall is an important trigger to breeding activity in natterjacks (Banks & Beebee, 1986a).

Breeding success, as judged by toadlet production, varied substantially between years when averaged over all sites (Fig. 3(A)). There was no significant correla- tion between the mean scores of all sites and those of successful sites (i.e. those with M > 0, as defined in Methods); except for 1976 and 1977, successful sites maintained consistent and high mean scores (always between 2.2 and 2-5). However, there was a significant negative correlation between the mean score of all sites and the arcsin-transformed percentages of sites failing totally (r15 -- -0.69, p < 0.01). Thus the variation seen in Fig. 3(A) was related to the number of sites failing completely rather than to large inter-year differences in the performance of successful sites. Most of these failures arose from premature pond desiccation, killing

Table 9. Effect of spring temperature on spawning data

Site Mean first spawn day

All years Warm Spring Cold Spring (n= 12) (n=6) (n--6)

Caerlaverock 121(2) 119(3) 123(4) Formby 104(3) 98(4) 110( 1)* Woolmer 111(2) 109(2) 112(2)

n, Numbers of years averaged in each category, grouping the six warmest and six coldest March + April periods separately. Data are given as day of year on which spawn first observed, averaged with standard errors in parentheses. *, Significantly different from warm spring, t = 2-61, p < 0-05.

116 B. Banks, T. J. C. Beebee, A. S. Cooke

LLI nr 0 L) r./j

z

LU

2.5

2.2

1.9

1.6

1.3

1.0

A

I I I I I I I I I I I I I I I I I I

72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

YEAR (19-1

(3 Z . - - I

LL (/) I.U I-- ~)

LL 0

50

40

30

20

10

B

o o

• •

• •

i f i O i i

- 2 0 0 - 1 3 0 - 6 0 10 80

SEPT-MAY RAINFALL CHANGE RELATIVE TO MEAN (turn}

i

150

Fig. 3. Variation in breeding success. A, Mean scores of toadlet production (see Methods) at all sites from which data were available (varying between years from 10-31) over the study period; B, Relationship between percentage of sites in which no toadlets were produced (M=0) and total rainfall over the preceding autumn + winter + spring period, mea- sured at a central locality (Monks Wood) in England. Each point represents data from a single year. Mean rainfall for

this period, 1973-1989, was 410 mm.

all the tadpoles prior to metamorphosis. There was a clear, inverse relationship between the percentage of sites failing completely and the total rainfall over the period of the breeding season and previous autumn and winter (Fig. 3(B)). Although spring (March-May) rainfall had a significant effect by itself on breeding success (r~ 5 = -0.48, p = 0.05), the strongest relation- ship was with precipitation over the longer period including winter when the water table is charged up to its annual maximum height. For years with below- average rainfall there was a significant negative rela- tionship (r9 = -0.71, p < 0-05). For years with above- average rainfall there was no relationship. The pattern of rainfall, as well as the total amount, was also impor- tant. There was an increased risk of breeding failure for those years when any single month between March and May was 'dry' (arbitrarily defined as <25 mm of rain;

Mann-Whitney U7.10=5.5, p < 0.05) irrespective of total September-May precipitation.

DISCUSSION

The efforts put into survey and monitoring of natter- jack toad populations since 1970 have resulted in this animal being one of the most thoroughly documented of all protected species in Britain, and arguably the most intensively studied case of amphibian decline in the whole of Europe. It is almost certain that nearly all British populations of Bufo calamita have been dis- covered, virtually all breeding ponds identified (there are probably between 250 and 300, depending on defi- nition), and estimates have been made of population sizes that indicate a national total of around 15 000 adults during the 1980s. This figure is based on simple addition of the highest spawn counts for each site, though this might yield a substantial overestimate if populations fluctuate between wide limits as expected in an r-selected amphibian (Banks & Beebee, 1988; Wilbur, 1990). A total based on average counts is much lower (7000-8000 adults), but this in turn is likely to be biased downwards because it is known that in dry years a substantial proportion of females do not visit the breeding sites (Denton, 1991).

Whichever is closer to reality, the natterjack was clearly much less abundant than its closest relative in Britain, the common toad Bufo bufo. Best current esti- mates for the latter species indicate the existence of some 35 500 non-garden sites (Swan & Oldham, 1989) and assuming a mean population size of 600 adults (Cooke, 1975) this provides an estimate for Britain of about 20 million. If correct, these estimates indicate the common toad to be about a thousand times more abundant than natterjacks in terms of both sites and numbers of adults.

A few of the British natterjack populations have been studied in some detail, often as part of investiga- tions into the autecology of the species (Beebee et al., 1982; Banks & Beebee, 1986a, b, 1987a, b, 1988; Bridson, 1977; Buckley, 1985; Smith et aL, 1973; Smith & Payne, 1980; Smith, 1990). There have also been a large number (at least 130) of unpublished reports since 1970 encompassing many more natterjack populations (listed in Beebee, 1989) as well as three PhD theses (Mathias, 1971; Davis, 1985; Denton, 1991). Analysis of informa- tion on natterjacks accumulated over two decades has made possible one of the few assessments of the bio- logical effects of radiation on wildlife (apparently negligible in this case) and identified elements of climate, particularly winter and spring rainfall, that impact significantly on breeding success of an animal at the edge of its range. If lower than average winter and spring rainfall is to be a feature of our climate in the future then this will have relevance for conservation strategies for this species both locally and nationally. It is also possible that continued monitoring of natterjack breeding success could be employed in future decades as a biological indicator of the impact of any climatic

Conservation of natterjack toad 117

change manifest as alterations in rainfall quantity or pattern. The well-documented status of the natterjack should also be useful as a baseline with which to com- pare the outcome of any future recovery programme for this species.

The natterjack data are particularly useful in allow- ing an assessment of the value of conservation legisla- tion. It is striking that there has been little or no net change over the past 20 years in the number of extant toad populations compared with the massive declines in the immediately preceding period. However, this simple sum overlooks a number of underlying factors. Extinctions have continued, and at a rate not notably different in the 10-year periods before and after the Wildlife and Countryside Act of 1981. The recent efforts at starting new populations by translocation experiments have helped offset this continued attrition, but there is little evidence to suggest that the species protection clauses of the 1981 Act have had any detectable impact on natterjack conservation (though this was at least in part due to failure to notify landowners and local authorities of the species' presence). SSSI or nature reserve status has proved increasingly successful in defending natterjack populations from a variety of threats. However, insidious scrub invasion, as a conse- quence of inadequate management, has if anything worsened and caused declines at some of the largest extant natterjack sites. Although there is scope to nego- tiate management agreements, under existing legislation it is not possible to require positive management ac- tions from unwilling landowners (even on SSSIs). This is a major limitation where habitats are subject to degradation by simple neglect. We recommend, on the basis of the experiences of the past 20 years, the follow- ing lines of action as the most important to secure British natterjack populations in future decades:

(1) For all natterjack populations currently outside SSSIs, the landowners should be identified and in- formed of the presence and protected ,status of this amphibian as a matter of urgency. The relevant local authorities and statutory bodies should also be in- formed.

(2) There should be urgent consideration of actions which could be taken to safeguard the habitat of those natterjack colonies currently unprotected by SSSI des- ignation.

(3) The problem of habitat deterioration, especially over-fixation of dunes, scrub encroachment on heath- land and the growth of rank vegetation on saltmarshes, should be tackled with the necessary vigour and re- sources wherever permitted by landowners.

(4) The problem of habitat degradation by neglect within SSSIs should be addressed to see if a practical solution is available.

(5) Fragmentation of the existing large natterjack populations should be prevented.

(6) Conservation effort should be directed towards maintaining and enhancing the small isolated popula- tions that are most vulnerable to extinction.

One further point of concern is that two of the main river estuaries with substantial proportions of the British natterjack population (Duddon and Solway) are under consideration for tidal barrage schemes, and two more (Alt and Ribble) are so close to the proposed Mersey barrage that accretion patterns, and therefore the future of the dune habitat, could be significantly affected. Barrages across the Solway or Duddon would alter the natterjack breeding pond tidal inundation patterns that are probably crucial to survival (Beebee et al., 1993) and thus put the future of the natterjack in Britain at substantial risk. A three-year project of research and proactive conservation measures for the natterjack is to be funded by English Nature starting in 1992 as part of the RECOVERY programme for endangered species, (1) to maintain and where appro- priate enhance existing populations, and (2) to conduct a translocation programme to restore the species to representative sites across its historical range. Thus threats to existing sites will be addressed and habitat management guidelines for the species developed. In addition, regional conservation strategies are being considered or developed. There is, therefore, some cause for optimism in the trends of the past 20 years but no reason at all for complacency.

ACKNOWLEDGEMENTS

A large number of people have been involved in the monitoring of natterjack sites over the past 20 years; it would be impossible to name them all, but our thanks extend to all these contributors. Particularly consistent among them have been Nature Conservancy Council staff Rob Bridson, Tim Clifford, Vin Fleming, David Henshilwood, Keith Payne, Rick Southwood, Dave Shaw, Dave Simpson, Graham Weaver, Dave Wheeler and Wally Wright; and in the non-Government sector major contributors have been Tony Bell, Bill Boyd, John Buckley, Peter Carty, Dave Coward, Keith Corbett, Jonty Denton, John Houston, Mark Jones, Paul Kirkland, Tom Langton, Trevor Piearce, Dave Race, Doug Radford, Paul Rooney and Phil Smith. A. D. Horrill and F. R. Livens carried out the radio- nuclide analysis on natterjack carcasses and advised on interpretation. A. Frost provided the meteorological data. We also thank all those English Nature regional staff who provided details of threats and damage to SSSIs with natterjacks over the past 20 years. Tony Gent and David Horrill have provided helpful comments on the manuscript.

REFERENCES

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Banks, B. & Beebee, T. J. C. (1986b). A comparison of the fecundities of two species of toad Bufo bufo and Bufo calamita from different habitat types in Britain. J. Zool. (Lond.), 208, 325-38.

118 B. Banks, T. J. C. Beebee, A. S. Cooke

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