UNIVERSITY OF HELSINKIDEPARTMENT OF APPLIED BIOLOGY

PUBLICATION no 4

NUMERICAL AND BEHAVIOURAL RESPONSES OFBREEDING DUCKS TO HUNTING AND DIFFERENT

ECOLOGICAL FACTORS

byVeli-Matti Väänänen

Department of Applied BiologyP.O. Box 27 (Latokartanonkaari 5-7)

FIN-00014 UNIVERSITY Of HELSINKIFINLAND

veli-matti.vaananen@helsinki.fi

ACADEMIC DISSERTATION

To be presented, with the permission of the Faculty of Agriculture and Forestry ofthe University of Helsinki, for public criticism in Lecture Room 2 of Viikki

Infocenter, Viikinkaari 11, Helsinki, on April 20th, 2001, at 12 o’clock noon.

Helsinki 2001

This thesis belongs to the field of Wildlife Management

Reviewed by

Doc. Mikael KilpiARONIA Center for Environmental ResearchSydväst Polytecnic & Åbo Akademi UniversityRaseborgsvägen 6-8FIN-10600 EkenäsFinland

Opponent

Prof. Harto LindénFinnish Game and Fisheries ResearchInstituteP.O. Box 6FIN-00721 HelsinkiFinland

Supervised by

Doc. Hannu PöysäFinnish Game and Fisheries ResearchInstituteJoensuu Game and Fisheries ResearchKauppakatu 18-20FIN-80100 JoensuuFinland

Veli-Matti Väänänen (pp. 1-21,paper II, illustrations)

Journal of Avian Biology (paper I) Finnish Zoological and Botanical Publishing Board (paper III) Wildlife Biology (paper IV and V)

ISBN 951-45-9909-8 (nid.)ISBN 951-45-9924-1 (PDF)ISSN 1457-8085Yliopistopaino, Helsinki 2001

and Prof. Erkki KorpimäkiSection of EcologyDepartment of BiologyUniversity of TurkuFIN-20014 TurkuFinland

To my sister,Anne Yliluoma (1957-1999)

List of original papers

The thesis is based on the following publications and manuscripts, which will be referredto in the text by their Roman numerals:_______________________________________________________________

I Väänänen, V.-M. 2000. Predation risk associated with nesting in gull coloniesby two Aythya species: observation and an experimental test. - Journal of AvianBiology 31: 31-35.

II Väänänen, V.-M. 2001. Message in the call - brood rearing ducks discriminatebetween call types of gulls. - manuscript

III Nummi, P. & Väänänen, V.-M. 2001. High overlap in diets of sympatricdabbling ducks - an effect of food abundance? – Annales Zoologici Fennici (inpress).

IV Kauppinen, J. & Väänänen, V.-M. 1999. Factors affecting changes in waterfowlpopulations in eutrophic wetlands in the Finnish lake district. – Wildlife Biology5: 73-81.

V Väänänen, V.-M. 2001. Hunting disturbance and the timing of autumnmigration in Anas species. - Wildlife Biology 7: 3-9.

Contents

1. Introduction 1

1.1. Adaptation against predation 1

1.2. Interspecific relationship: the role of food partitioning indabbling ducks 2

1.3. Weather and habitat factors affecting duck populations 3

1.4. Hunting vulnerability and disturbance effect 4

1.5. Finland as a waterfowl breeding and harvesting area 5

1.6. Aims of this thesis 5

2. Study area, material and methods 6

3. Main results and discussion 7

3.1. The gull colony: a “protective umbrella” for breedingducks 7

3.2. The role of food resources in eutrophic wetlands 8

3.3. Do weather factors cause changes in waterfowl populations? 9

3.4. Hunting pressure of waterfowl in Finland 10

3.5. Hunting disturbance and distribution of ducks 13

4. Management implications 13

Acknowledgements 14

References 15

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1. Introduction

1.1. Adaptation against predation

Predation is one of the most importantfactors affecting the survival of birds(Lack 1968, Wiens 1989). During theirlife span, birds are subject to differentkinds of predation and many features oftheir behaviour (e.g. flocking andwarning behaviour, nest remaining) areadaptations against predation (Wiens1989, Lima & Dill 1990). Evolution ofcryptic coloration of breeding females isalso important for making incubatingfemales more difficult to detect bypredators. For example, dabbling ducks(e.g. the mallard Anas plathyrhynchosand the teal Anas crecca) moult someupper wing coverts, tertials and some tailfeathers during spring to have morecryptic coloration (Salminen 1983).However, predation on adult ducks has arather limited impact on waterfowlpopulations (Owen & Black 1990). InStoudt and Corwell’s (1976) survey,predation (excluding hunting by man)represented only 0.14 % of naturalmortality of adult waterfowl. Unlikepredation on adult birds, nest predation isan important factor affecting reproductivesuccess of birds (Ricklefs 1969, Owen &Black 1990, Sargeant & Raveling 1992,Martin 1993), and many adaptationsagainst nest predation have developed(Lack 1968).

Among ducks, nest siterequirements and means of avoidingpredation vary between species (Owen &Black 1990). Duck species nesting in theforested boreal regions of northernEurope nest over a wide area (e.g. themallard, the wigeon Anas penelope, theteal and the goldeneye Bucephalaclangula) and their nests are difficult todetect by predators. Species nesting in

eutrophic wetlands prefer certain habitattypes. The pintail Anas acuta, theshoveler Anas clypeata and thegarganey Anas querquedula prefer openshores, meadows or fields, the pochardAythya ferina and the tufted duckAythya fuligula floated vegetation standsand the coot Fulica atra dense stands ofemergent vegetation from the previousyear (e.g. Cramp & Simmons 1977). Inwetlands and fields, corvids (especiallythe common crow Corvus corone) arethe most important nest predators ofbirds (e.g. Hildén 1964, Gailbraith 1988,Götmark & Åhlund 1988, Bains 1990,Berg et al. 1992, Valkama et al. 1999).Crows systematically search certainhabitat types and clumped nests aremore vulnerable to crow predation thanthose on dispersed habitats (Tinbergenet al. 1967, Croze 1970). Mammalianpredators may also have an importantrole in decreasing breeding success ofbirds in wetlands, fields and forests(Putaala & Hissa 1993, Viksne 1997,Virtanen et al. 1998, Pöysä 1999,Valkama et al. 1999).

It is obvious that the nest predationrates vary remarkably between areas andspecies. The nest predation rate of thecavity-breeding goldeneye is probablythe best known of ducks in inland areasof northern Europe. Studies have shownthat in central Finland about 5%, insouth-east Finland 33-74% and in twoareas in Sweden 10% and 38% of nestsare preyed upon (Erikson 1979, Fredga& Dow 1984, Pöysä 1999, Ruusila et al2000.

Some species nest in associationwith aggressive colonial breeders (e.g.larids) or close to the nests of birds ofprey to avoid nest predation (Hildén1964, Newton & Campel 1975,Götmark & Anderson 1980, Wiklund1982, Norrdahl et al. 1995, Larsen &

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Grundetjern 1997, Pius & Leberg 1998,Valle & Scarton 1999). Three hypotheseshave been suggested to explaininterspecific nesting associations in birds.According to the protector specieshypothesis, an aggressive species defendsits nesting area and all nests in this areagain protection (Hildén 1964, Newton &Cambell 1975, Wiklund 1982).According to the “informationparasitism” hypothesis, individuals canexploit information of species’ alarmcalls (Nuechterlein 1981, Burger 1984,Pöysä 1989). Finally, it has beensuggested that a mixed breeding colonycan function as an information centre forfood finding (Ward & Zahavi 1973). Firstand second hypotheses have beenexperimentally tested and results supportthe predictions of these hypotheses(Nuechterlein 1981, Götmark 1989). Theinformation centre hypothesis hasreceived only observational support(Krebs 1974, Emlen & Demong 1975).However, it has been pointed out that anexplanation solely based on food findingseems unrealistic in a species that feed indifferent locations and on different foods(Lack 1968, Krebs 1974, Erwin 1979).

1.2. Interspecific relationships: therole of food partitioning indabbling ducks

Resource partitioning is one of the basicaspects in community ecology when theco-occurrence of different species isconsidered. A species functional role in acommunity and its position in trophicinteractions are important. Niche size,shape, location and overlap with otherspecies will shift in response to changesin competitive pressure (Wiens 1989).Ecomorphological patterns of species,e.g. bill morphology, have been suggested

to reflect resource competition.However, it is obvious thatmorphological structures of species arelikely to reflect a compromise solutionunder several types of selection pressure(Wiens 1989). Species with a similarecology will form ecological guilds. In acompact guild, the partitioning oflimited food resources and/or flexibilityof food use makes coexistence ofspecies possible (Wiens 1989, 1993).

Many community ecologicalprinciples appear to be valid inwaterfowl communities; for instance thespecies richness and especially breedingdensities are highest in the mostproductive areas (Elmberg et al. 1993,Kauppinen & Väisänen 1993,Kauppinen 1997). Waterfowlcommunities also have a clear guildstructure; e.g. dabbling ducks form acompact foraging guild (Pöysä 1983a,Pöysä et al. 1994). All species in thedabbling duck guild occurs togetheronly in most productive wetlands inNorth Europe (Elmberg et al. 1993,Kauppinen & Väisänen 1993).

There has been long-standingdebate on the importance of bill lamellardensity (Nudds & Bowlby 1984, Nuddset al. 1994), neck length (Pöysä 1983b,Pöysä et al. 1994) and foragingbehaviour (Pöysä 1987, Nummi 1993)as well as on the role of habitat structurein food partitioning among dabblingducks (Nudds et al. 2000). Results fromNorth America suggest that interspecificvariation in the density of bill lamellaereflects microhabitat segregation (Nudds& Bowlby 1984, Nudds 1992, Nudds etal. 2000, see also Nudds et al. 1994).Species in North America with fewlamellae, but large bodies, tend to feedin shallow, vegetated microhabitatswhere invertebrate prey is large. On theother hand, species with dense lamellae

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tend to occur in open microhabitats whereprey is smaller (Nudds et al. 2000). Innorthern Europe, however, the evidencesuggests the opposite (see Pöysä et al.1996), indicating that it is the differencein body length that facilitates coexistence,by constraining the depths to which duckscan “up-end” to reach food in submergedvegetation (Nudds et all. 2000). However,with regard to the proposed associationbetween bill lamellae density and preysize, our understanding of current duckcommunity ecology is still mostly basedon Nudds and Bowlby’s (1984) literaturesurvey on studies done in different partsof North America.

1.3. Weather and habitat factorsaffecting duck populations

During the 1900‘s many waterfowlspecies expanded into northern Europefrom the south and south-east (Kalela1946, Yarker & Atkinson-Wiles 1971,von Haartman 1972, Burton 1995,Hagemeijer & Blair 1997). Changes indistribution of species have beensuggested to be mostly due to changes inhabitats and/or climate (e.g. Kalela 1949,von Hartman 1973, Burton 1995,Hagemeijer & Blair 1997). During thelast century, eutrophication in Finland hascreated favourable habitats fornewcomers, and several new species (e.g.the coot, the gadwall Anas strepera andthe pochard) have established theirpopulations in well-vegetated wetlands.

Extremely harsh winters haveaffected short-term populationfluctuations of waterfowl in North Europe(von Haartman 1945, Hildén 1964,Nilsson 1979, 1984). A severe wintercould increase mortality on the winteringgrounds, make waterfowl morevulnerable to hunters and could also

indirectly (e.g. by lowering physicalcondition) affect breeding success of thenext season (Boyd 1964, Nilsson 1979,1984, Andersen-Harild 1981, Newton1998). In addition, spring temperaturesmay shorten or lengthen migration (Siira& Eskelinen 1983), and summertemperatures may have an effect onbrood production.

In North America, a high variationin population size of ducks betweensuccessive years has traditionally beenassociated with unpredictable changes inhabitats (Evans & Black 1956, Eisenlohr1969, Posphala et al. 1974; but seeBethke & Nudds 1995). Wetlands inpothole areas of northern prairies andparklands have been shown to beunstable due to weather factors; waterlevel fluctuates widely both betweenyears and during the breeding season.Changes in habitat quality (drought)also cause between-year variation inbrood production (Leitch & Kaminski1985, Sutherland 1991), and, broodproduction may affect the size ofbreeding populations in the subsequentyears (Reynolds & Sayer 1991).

In northern Europe the quality ofduck habitats does not vary muchbetween or within years (Nummi &Pöysä 1993), and, hence, variation ofhabitat quality should not be animportant determinant of population sizeor brood production of ducks. Unlike inNorth America, changes in size ofwaterfowl populations or structure ofduck communities are usually not largeduring successive years (Pöysä 1989,Kauppinen 1995).

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1.4. Hunting vulnerability and dis-turbance effect

Hunting is one of the most importantmortality factors of fledged waterfowl(Stoudt & Cornwell 1976, Rogers et al.1979, Owen & Black 1990). Mortalitydue to hunting in ducks is age-specific.Young ducks are shot more than adults(Anderson 1975, Kremetz et al. 1987,Nichols et al. 1990, Johnson et al. 1992,Caithness et al. 1991) and usually moremales are shot than females (Anderson1975, Reinecker 1976, Nichols et al.1990). Furthermore, brightness ofcoloration (Metz & Ankney 1991),diseases (Bellrose 1959), flockingbehaviour (Olson 1964, Dufour &Ankney 1995) and especially physicalcondition (Hepp et al. 1986, Reinecke &Shaiffer 1988, Heitmeyer et al. 1993, butsee also Sheeley & Smith 1989) seem toaffect vulnerability to hunting. Ducks inlarge flocks in good physical condition(abundant fat reserves) can avoid huntingmost efficiently (Hepp et al. 1986,Reinecke & Shaiffer 1988, Heitmeyer etal. 1993, Dufour & Ankney 1995).

The mortality of waterfowl variesfrom year to year and, in theory, mortalitydue to hunting can be compensated tocertain degree by a decrease in mortalitydue to other causes (Anderson &Burnham 1976, Patterson 1979, Rogers etal. 1979, Nichols et al. 1984). However,compensation of mortality due to huntingis possible only if other mortality factorsare density dependent (Newton 1998).The timing of hunting is crucial in thecompensation process; mortality due tohunting during autumn is more easilycompensated for than that occurring inwinter (Mc Gowan 1975, Kokko &Lindström 1998, Kokko et al. 1998,Newton 1998). In geese mortality due tohunting has been additive, and therefore,

increased the total yearly mortality rate;after hunting limitation geesepopulations have increased rapidly(Owen & Black 1990, Newton 1998).

Natal philopatry and age-specificreproductive success are importantfactors in management of waterfowlpopulations. Local hunting can have adirect effect on population size in lateryears if the harvesting rate is too high,because of natal and breeding sitephilopatry of female ducks (Greenwood1980, Clarke et al. 1997, Ruusila 1999).Therefore, the most valuable individualsin waterfowl populations areexperienced females which produce thelargest clutches and broods, morerecruits and, in particular, nest in thesame area year after year (Mihelsons etal 1986, Sæther 1990, Forslund &Larsson 1992, Rohwer 1992, Forslund& Pärt 1995, Milonoff et al. 1998,Ruusila et al. 2000).

In addition to mortality, huntingalso has a disturbing effect on waterfowl(see reviews of Davidson & Rothwell1993, Madsen & Fox 1995). Huntingdisturbance has been shown to affectwaterfowl behaviour, such as increaseescape-flight distance, modify diurnalactivity and decrease daily foraging time(Owen & Williams 1976, Owens 1977,Gerbes & Repmeyer 1983, Madsen1985, 1998a, Mayhew 1988). There aredifferences between species insensitivity to disturbance and inwintering/staging areas. The mostsensitive species are those which stayclose to the coast or inland waters andare concentrated in relatively largeflocks (Madsen et al. 1998). Periods oflowest nutrient reserves and/or increasedenergy expenditure are most critical tohunting disturbance (Madsen & Fox1995, Dehorter & Tamisier 1998).

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Hunting disturbance may cause alocal and also a large-scale regionalredistribution of ducks (Lorentsen 1988,Madsen & Jepsen 1992, Follestad 1994,Madsen 1998b). Our knowledge of thelarge-scale effects of hunting disturbanceon waterfowl distribution is scarce. Moststudies on the disturbance effects ofhunting, have been carried out in stagingor wintering areas (Madsen & Fox 1995).

1.5. Finland as a waterfowl breedingand harvesting area

Within Europe, Finland is one of the mostimportant duck breeding areas. Forinstance, a central part of the Europeanpopulation of the following species breedin Finland: the goldeneye (about 60% ofthe European population), the goosanderMergus merganser (45%), the red-brestedmerganser Mergus serrator (39%), thewigeon (23%), the eider Somateriamollisima (21%), the teal (15%), thepintail (10%) and the shoveler (10%),(Hagemeijer & Blair 1997, Väänänen2000). Hence, conservation andmanagement of waterfowl habitats inFinland is very important for Europeanwaterfowl populations.

In Europe, waterfowl hunting is apopular recreational activity, especially instaging and wintering areas, but also inbreeding areas such as Finland. Thehunting bag of waterfowl in Europe hasbeen increasing and about 11 millionducks and geese are shot annually byapproximately 3.2 million hunters (Scott1982, Owen & Black 1990). The annualhunting bag in Finland has been almostone million ducks (Ermala 1992, SuomenVirallinen Tilasto 1997, see also SuomenVirallinen Tilasto 2000).

In the course of a year, waterfowlare distributed in an exceptionally large

area as compared with other game birds.The distances between the breeding andwintering areas may be thousands ofkilometres (Cramp & Simmons 1977,Owen & Black 1990). The mostimportant wintering areas for ducksbreeding in Finland are the southernBaltic and north-west Europe, thesouthernmost wintering areas being inAfrica (Väänänen 1999, FinnishMuseum of Natural History unpubl.data).

Thus, the waterfowl populationsare common for large areas acrossEurope. The population estimates ofmost waterfowl species in winteringareas of Europe have shown increasingtrends. However, the populations of thepochard and the pintail have decreased(Monval & Pirot 1989, Rose & Scott1997). It has been suggested thathunting has not caused the decrease ofthese two species (Layndry 1990).

1.6. Aims of this thesis

In this thesis, I examine numerical andbehavioural responses of waterfowl todifferent biotic and abiotic factors atindividual, population and communitylevels. In paper I and II, I studiedbreeding association between ducks andsmall colonial larids, i.e. the commontern Sterna hirundo, the black-headedgull Larus ridibundus and the little gullLarus minutus. In paper I, I focused onnest predation risk in the pochard andthe tufted duck and tested the hypothesisthat gull colonies protect ducks againstnest predation. In paper II, I focused onthe association between ducks and gullcolonies during the brood period.

In paper III, I focused on the sizedistributions of invertebrates in the dietsof dabbling ducks, and on the proposed

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association between bill lamellae densityand mean prey size in the diet of ducks. Idirectly compared the feeding niches ofsix dabbling duck species from the samelakes from which the prey availabilitydata were collected. I briefly discussedthe role of food in limiting numbers ofducks in eutrophic wetlands.

In the last two papers I studiedfactors affecting changes in waterfowlpopulations breeding in Finnish inlandlake area. In paper IV I examined recentchanges in the breeding numbers inrelation to weather factors and huntingpressure in the northern part of theFinnish inland lake area. In paper V Istudied hunting disturbance, refuge useand timing of autumn migration ofdabbling ducks. In addition, I examinedhunting bag (wing data) in relation tobreeding and autumn populations, to givea more detailed picture on huntingpressure of waterfowl in the studied sites.

2. Study area, material andmethods

Data were gathered from central andsouthern Finland from the period 1970-2000. The study areas in central Finlandconsist of both richly vegetated lakessurrounded by cultivated fields or usuallya narrow forest line on a shore and shoresof more urban sites. Dominant vegetationstands in eutrophic wetlands consist ofhorsetail Equisetum fluviatile, reedPhragmites australis, bullrushSchoenoplectus lacustris and sedgesCarex spp., whereas reed and sedges arecommon on urban shores. The mostimportant study wetlands are located inMaaninka (63°N, 27°E), in northern partof the Finnish inland lake area (Fig 1).Data from southern Finland are from

lakes and shores of the Helsinki area(60°N, 20°E) and from moreoligotrophic lakes and ponds in theNuuksio lake area. Stands of reed aredominant in the Helsinki area andsedges in the Nuuksio lake area.

Figure 1. Distribution of study areas. Mostimportant study area is marked as blacksquare (include ten study wetlands). Studyareas in southern Finland (Helsinki areaand Nuuksio lake area) are marked as opensquare.

Data on pochard and tufted ducknests were gathered in Maaninkabetween 1985 and 1996 (I). The nestpredation experiment was carried out inMaaninka and Lapinlahti (63°N, 27°E)in 1998. In the experiment artificialnests were placed within a gull colony(ten nests with one hen Gallusdomesticus egg in each) and an equalnumber of control nests well outside thedefence area of the colony on the samelake or nearest suitable wetland (I). Theexperiment included six replicates.

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Distribution of duck broods (withinor outside gull colony) was observedbetween 1998 and 2000 and data weresummarised as broods within or outsidethe defence area of a gull colony (II).Shorelines of study lakes with a colonywere calculated using the Mapinfoprogram (Mapinfo Professional Version5.0.1, copyright 1985-199 MapinfoCorporation). The playback experimentwas conducted in 1999 and 2000. Alarmand basic (as a control) calls of black-headed gulls were played to each femaleduck with brood. The experiment testedwhether a brood rearing female duckdistinguishes between alarm and basiccalls of gulls (II).

Data for paper III were collected inMaaninka. The esophagi of dabblingducks were removed after the ducks wereshot and preserved in alcohol pendinganalysis for diets between 1992 and 1998(Swanson & Bartonek 1970). Foodavailability data were collected usingactivity traps and corer (see Nudds &Bowlby 1984, Nummi 1993, Nummi etal. 1995). Data were summarised andanalysed according to methods used byNudds and Bowlby (1984) to allow directcomparisons.

Data on the breeding pairs (IV) wereobtained from the northern part of Finnishinland lake area from the period 1970-1998. Data on the effect on huntingdisturbance (V) were obtained fromnorthern part of Finnish inland lake areafrom 1995 to 1999. Duck ringing data arefrom the period 1970-1991 (IV). Wingdata are gathered in the Maaninka areabetween 1985 and 1989 and data includeabout 30% of annual bag (IV).

To give a clearer picture of huntingpressure in eutrophic wetlands in centralFinland, wing data from the mostimportant study lakes (four lakes, totalarea 2.92 km2) gathered from 1985 to

1998 were analysed. The wing datacomprise about 40% of annual bag. Theestimate is based on numbers of huntersand bag statistics of local huntingassociation in the study area. In this areathe annual bag was compared withbreeding and autumn numbers ofdabbling ducks. The age and sex of eachbird was determined from the wingsample according to Salminen (1983).The development status of juveniles(primaries full grown or undeveloped)and moulting phase of adult ducks (wingmoulting not yet started, primaries weregrowing or have already changed) wasdetermined. The census of the dabblingducks in each wetland was taken justbefore the opening of the huntingseason, i.e. between 17 and 19 August(mostly 18 or 19 August), (V, thisstudy). The timing of the autumnmigration was observed in two wetlandsfrom the middle of July to the end ofice-free period over the 1995-1998period (V).

3. Main results and discussion

3.1. The gull colony: a “protectiveumbrella” for breeding ducks

Gull colonies have an important role inthe nesting success of ducks (I). I foundthat aggressive gulls protect nests withintheir colony area as the protector-species hypotheses predicts (I, Götmark1989, see also Larssen & Molsvor 1992,Norrdahl et al. 1995, Larssen &Grundetjern 1997, Pius & Leberg 1998).The predation rate of pochard and tuftedduck nests within colony was less than10 %, whereas outside the gull coloniesit was about 48% and 40 %, respectively(I). Experimental testing with artificialnests also showed that a higher

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proportion of nests was preyed uponoutside than within the colonies (0.98 and0.13, respectively) (I). The predation rateof pochard and tufted duck nests was high(I), but even higher predation rates amongducks and geese have been reported (e.g.Summers & Underhill 1987, Pöysä 1999).

Götmark (1989) suggested that thetiming of nesting may be an importantfactor in the evolution of nestingassociation between ducks and larids aswell as between birds and their predators(Wiklund 1982, Norrdahl et al. 1995,Larssen & Grundetjern 1997). Within thegull colony nests were protected when thelaying period of ducks began at the sametime or after that of the larids (Götmark1989). However, extremely late clutchesmay be left without protection whenfledged gulls leave the colony area.Pochard and tufted duck lay their eggslater than black-headed gull, so, myresults support Götmark’s (1989)suggestion. However, it is obvious thatthere may be other factors, such as nestsite requirements, affecting the evolutionof the nesting associations. My resultsshow that the tufted duck nested moreoften within colonies than the pochard. Ifound that the pochard favour smallerfloated vegetation stands than the tuftedduck (I). Because black-headed gullsmostly start laying before pochards, it ispossible that small vegetated islands arecolonised first by gulls, and hence,pochards may nest more often outside acolony even though the nesting successrate within the colony area is better.Therefore, the nest site requirements mayexplain differences in the nestingassociation with gulls between pochardsand tufted ducks (I).

Gull colonies are also important forducks during the brooding season (II).Broods of most duck species areprevalent in the defence area of colonies

and only the territorial goldeneye do notclump within a colony (II). Nuehterlein(1981) showed that grebes can utiliseterns’ alarm calls, and furthermore,Burger (1984) found that grebes nestingwithin gull colonies had better survivalrates than grebes nesting outside thecolonies. These findings indicate thatgrebes can exploit the warningbehaviour of terns, and hence, reducepredation. Among ducks, foraging tealshave been found to respond to alarmcalls of the black-headed gull (Pöysä1988). My “playback” experimentconfirmed the ability of ducks todistinguish information of black-headedgull calls without using visual cues (II,see Neuchterlein 1981). It may alsosuggest that female ducks can use thevisual cues of attacking and mobbinglarids, and it is probable that by usingthis information for early warning,broods can avoid predation.

As a whole, gull colonies areimportant for breeding ducks, especiallyduring the nesting phase (I). During firstweeks of the brooding season, whenbroods are the most vulnerable toloosing ducklings (Ortmeyer & Ball1990, Savard et al. 1991, Talent et al.1983, Mauser et al. 1994, Pöysä &Virtanen 1994), larids may also have animportant role as protector species andact as early warners to ducks (II).

3.2 The role of food resources ineutrophic wetlands

I found a high overlap in food useamong the dabbling ducks in eutrophicwetlands. I suggested that the overlap offood in the dabbling duck guild may notbe exceptional (III). High diet overlap isusually associated with “fat” times withabundant food, and low diet overlap

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with “lean” times (Smith et al. 1978,Rotenberry 1980, Rosenberg et al. 1982,Schoener 1986, Wiens 1989). The highdiet overlap seen in my study may thusindicate low food competition betweendabbling ducks. This can be seen in thediet patterns of teal and mallard (thesmallest and largest species in thedabbling duck guild). In my study thediets of mallard and teal overlappedconsiderably, whereas in another studybased on data from oligotrophic lakes thediets of the two species clearly differed(Nummi 1993).

Unlike in more oligotrophicwetlands (see Nummi et al. 2000, Sjöberget al. 2000), food abundance hardlylimited breeding densities or compositionof duck communities in eutrophicwetlands (III). North European dabblingducks coexist only in eutrophic wetlands(with abundant food), and some species,i.e. the shoveler and the garganey, do noteven breed outside lush wetlands (e.g.Kauppinen 1993, Hagemeijer & Blair1997, Väisänen et al. 1998). It seemspossible that an abundant food supplyenabled a high overlap in food use, andthat resource competition may not be animportant factor in affecting breedingdensities or brood production in eutrophicwetlands.

3.3. Do weather factors cause chan-ges in waterfowl populations?

There was a 40 % difference betweenmaximum and minimum of the totalwaterfowl population in our study area.However, between successive yearsfluctuations did not exceed 20 % (IV).The most unstable species were thegarganey, the tufted duck, the coot andthe pochard (IV). It has been suggestedthat weather factors may cause short-term

fluctuations of waterfowl populations innorthern Europe (von Haartman 1945,1957, Greenquist 1965, Hildén 1966,Nilsson 1979, 1984). In particular, ahard winter may be associated withpopulation fluctuations by causing directwinter mortality or by indirectlylowering the breeding success in thefollowing summer (e.g. Boyd 1964,Nilsson 1979, 1984, Andersen-Harild1981). In my analyses, the followingweather factors appeared to beassociated with population fluctuationsof the species; in the garganey: springtemperature; in the pintail: brood seasontemperature, winter severity in Franceand spring temperature; in thegoldeneye: winter severity in the Balticand spring temperature; and in themallard: brood season temperature inthe previous year (IV).

Some species seem to be sensitiveto spring temperatures which has beensuggested to cause fluctuations insouthern/northern species at the limit oftheir distribution area (IV, Siira &Eskelinen 1983). The garganey isperhaps the best-known example beingmore numerous after warmer thanaverage springs (IV, Siira & Eskelinen1983). Abnormal climatic conditionsduring spring should affect more first-time breeders than older females that arenest site philopatric. Hence, we foundsome support for the idea that weatherfactors may affect short-term fluctuationof waterfowl populations but, in general,climatic factors seem not to play animportant role in population fluctuations(IV).

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3.4. Hunting pressure of waterfowlin Finland

Information of duck reproduction inFinland and in other parts of northernEurope is scarce. In their study from theoligotrophic Evo area in southern FinlandNummi and Pöysä (1997) reported thefollowing numbers of young per breedingpair: the teal 1.5, the mallard 1.4 and thegoldeneye 1.3. It is obvious that in eut-rophic wetlands offspring production ishigher (see Nummi & Pöysä 1997), eventhough nest predation rates may also behigher at these sites (I). In Finland, theannual waterfowl bag has been almostone million birds (Ermala 1992, SuomenVirallinen Tilasto 1997, see also SuomenVirallinen Tilasto 2000). The total bag ofwaterfowl in Finland in relation to thebreeding population or brood production(Nummi & Pöysä 1997, Väisänen et al.1998) seems to be high (bagged water-fowl/breeding pair in hunting season1994/95: the bean goose Anser fabalis3.9, the greylag goose Anser anser 1.5,the mallard 1.8, the teal 1.0 and the gol-deneye 0.9; Väänänen 2000). Accordingto Finnish ringing data (ducks ringed asyoung) most of the recoveries of shotducks are found in Finland, in particular,near natal areas (Väänänen 1996).However, we lack the knowledge of therespective sites of origin of waterfowl inthe bag. Moreover, it is obvious that a lotof waterfowl shot in Finland migrate fromRussia.

The breeding population of thegoldeneye has been studied intensivelysince 1984, in my study area all hatchedducklings have been ringed in an area ofabout 280 km2 (Pöysä et al. 1997). Theproportion of ringed goldeneyes (ownpopulation) in the bag in 1985-1998 hasbeen over 30% at the beginning of thehunting season and still clearly over 20%

in the middle of September (Fig 2). Thisresult shows that the proportion of thelocal goldeneye population bagged ishigh in eutrophic wetlands. The reco-very data of the goldeneye show thateven at the beginning of the huntingseason some juvenile goldeneyes haveregularly been found far from their natalarea, whereas recoveries of mallardshave been made only in their natal area(Väänänen 1992, Runko unpubl. data).This implies that, at the beginning of theopen season, fledged juvenile mallardsmay be more numerous in their respec-tive natal area than goldeneyes (see alsophenology of autumn migration ofmallard in V), and, hence, mallards mayface more serious losses due to localhunting in natal areas.

Figure 2. Proportion of ringed goldeneyes(n=108 ringed goldeneyes) in the huntingbag in four study wetlands in the 1985-1998period. Results are shown in 10-day periods,and the first day of each period is given un-der the bar and the total number of observa-tions in the top of the bar. Data consist onlyfor those ringed goldeneyes which are collec-ted from hunters during wing sample survey.The total number of bagged goldeneye is377.

Eutrophic wetlands are the mostpopular duck hunting areas. In my eut-rophic study wetlands hunting pressure

0

5

10

15

20

25

30

35

40

20.8

30.8 9.9

19.9

29.9

9.10

19.1

0

Pro

port

ion

rin

ged 262

27

27

17

25

12 7

12

Table 1. The proportion of bagged adult duck females of different species in relation to breedingpopulation (A) and percentage of females in different moulting phase (B-E) in wing data during1985-1998 in four wetlands in Maaninka. The bag was calculated from wing data by assumingthat wing data are 40% of the total annual bag in the study area. Moulting phase of adult females(analyzed from wing samples) was divided into four categories: B = wing moulting has not yetstarted, C = primaries growing, D = primaries full grown, but base of primaries are still soft, E =primaries are fully developed. Total numbers of bagged adult females (wing samples) are shownin column F.

Species A B C D E F

Wigeon 0.93 6.5 47.7 4.7 41.1 107Teal 0.80 4.4 41.3 11.5 42.9 182Mallard 2.00 5.2 37.0 8.1 49.6 135Pintail 0.25 11.5 57.7 15.4 15.4 26Shoveler 0.08 16.7 58.3 8.3 16.7 12Garganey 0.13 - 83.3 - 16.7 6Pochard 0.03 100.0 - - - 1Tufted duck 0.20 47.1 23.5 5.9 23.5 17Goldeneye 0.03 - 100.0 - - 1

Total 7.4 42.7 8.9 40.9 487

In Finland the proportion of baggedadults in relation to the breedingpopulation can be high, particularly in mystudy area where adult females ofmallard, teal and wigeon are shot in greatnumbers (Table 1). The timing ofmoulting and moulting strategy ofsuccessful breeders is extremely critical.The breeding dabbling duck females facelocal hunting in breeding areas bymoulting near their breeding areas,whereas goldeneyes and pochards avoidlocal hunting by migrating to moultinggrounds (see Salminen 1983). It isobvious that in the beginning of thehunting season the adult dabbling duckfemales belong to a local population(mostly moulting) whereas most of thefemales bagged late in autumn, originatedoutside the study area.

In the total annual bag in thestudied area, half of the adult duckfemales had growing or old primaries(Table 1). Breeding females begin theirwing moulting after or slightly before(renester) juveniles are fledged, whereasthe unsuccessful breeders already havenew primaries at the beginning ofhunting season. In my study area, thefirst broods of mallard and wigeon arefledged usually in the last week of Julyor at the beginning of August. It takesabout one month to moult primaries, andfemales are flightless for about 2/3 ofthe moulting period (see Salminen1983). Therefore, successful breeders ofmallard and wigeon have not enoughtime to finish wing moulting before theopening of the hunting season. Myresults indicate that successful breedersin particular are vulnerable to hunting.

13

This is unfavourable, because thosefemales are the most valuable part ofwaterfowl population (see Sather 1990,Forslund & Larsson 1992, Rohwer 1992,Forslund & Pärt 1995, Milonoff et al.1998, Ruusila et al. 2000).

3.5. Hunting disturbance and dist-ribution of ducks

About 200 000 duck hunters participate inthe first day of the open season for ducksin Finland (Ermala & Leinonen 1995). Itis well known that hunting has strongdisturbance effects on waterbirds (seereviews by Davidson & Rothwell 1993,Madsen & Fox 1995). I found thatimmediately after the opening of thehunting season the numbers of dabblingducks collapsed and hunting caused aclear local redistribution (V).

In Finland there are no large-scaledata available for estimating the effect ofhunting disturbance on the regional/national distribution of ducks. However,because local-scale disturbance effectsseem to be common at least in the inlandlake district, it seems that regionalchanges in the distribution of dabblingducks are also possible (V). In general,knowledge of large-scale redistributioncaused by hunting is scarce (Madsen &Fox 1995). However, the early massdeparture of pink-footed geese Anserbrachyrhynchus in Denmark and greylaggeese in Norway have been ascribed tothe disturbance caused by hunting(Lorentsen 1988, Madsen & Jespen 1992,Follestad 1994).

Waterfowl have been reported toseek shelter in refuge areas. Furthermore,in Denmark numbers in quarry dabblingducks increase 4 to 50-fold after reservewas established (Madsen & Fox 1995,Madsen 1998a). My results indicate that

the redistribution pattern betweenhunting and refuge areas is also thesame in my study areas. After thebeginning of the hunting season, ducksuse reserves more than hunting areas (V).

4. Management implications

Many functional characteristics of aspecies - i.e. adaptations against preda-tion, morphological feeding structures,foraging and flocking behaviour - mayreflect compromise solutions underseveral types of selective pressure (Lack1968, Wiens 1989). The selective forcesmay operate either in evolutionary orecological time scale. Also, in widelyranging species the patterns that we seelocally may reflect selection pressuresthat are promoted elsewhere. Forexample, waterfowl use several kinds ofhabitats within year and during life-spanthey have diverse intra- and interspesificinteractions. These factors may shapeboth duck population fluctuations andwaterfowl communities and have diffe-rent effects on population fluctuation ofwaterfowl. In waterfowl management, itis crucially important to have large-scaleknowledge of species’ ecology.

My results suggest that gull colo-nies may increase breeding success ofducks, especially by providing safenesting sites. It is important that habitatrequirements of small colonial larids aretaken into account in the conservationand restoration of wetlands. This is evenmore timely because numbers of black-headed gull, the most important protec-tor species of ducks, have decreased inmany parts of Finland (Väisänen et al.1998, Ruokolainen et al. 1999).

Habitat quality, especially asmeasured by food abundance andavailability, is an important factor

14

affecting the density of breeding duckpairs and broods (e.g. Nummi & Pöysä1993, Nummi et al. 2000, Sjöberg et al.2000). If the food availability is below theresource-limitation level (see Wiens1993) food resources may affect thepopulation density and community struc-ture of ducks. However, the extensivefood overlap of dabbling ducks in thewetlands of my study indicates that foodresources may not limit duck populationsin eutrophic wetlands. Other factors, suchas hunting, may keep some duckpopulations (e.g. mallard) under carryingcapacity. Therefore, in eutrophic wetlandsthere is no need to manage foodresources.

At least in eutrophic wetlands ofcentral Finland hunting pressure ofwaterfowl seems to be high. Most of thehunting of the Finnish ducks population isdone near natal areas, not in staging orwintering areas, though there aredifferences in harvesting rates betweendifferent species and different areas. Itseems evident that early migrants areheavily hunted much in wintering areas,whereas late migrating species, except theteal, are harvested mostly in Finland (seeVäänänen 1996). However, in general,duck populations have tolerated huntingin Finland surprisingly well. We areresponsible for the management ofespecially those species in which most ofthe European population breeds inFinland, e.g. common goldeneye andgoosander.

In Finland we have a lot of shoresand wetlands within towns and villageswhere hunting is not allowed because ofhuman settlement and recreationalactivity. However, we lack refuges ofhigh quality feeding and moultinghabitats for waterfowl. In Finland, there isa need to establish a network of reservesfor waterfowl in eutrophic wetlands, as

has been done in Denmark (Madsen &Fox 1997, Madsen et al. 1998). Themain functions of such a network are: (i)to provide undisturbed high qualitymoulting areas for breeding femaleducks, (ii) to provide high qualityundisturbed feeding habitats, and (iii) toprevent the early mass departure of wa-terfowl due to hunting disturbance. Co-operation in the management of water-fowl populations between breeding,staging or wintering area is of crucialimportance.

Acknowledgements

My interest in waterfowl is originatedfrom my childhood. I observed thewildlife of wetland habitats when I wastrapping muskrats on my “home lake”Valkeinen with my father. Later JukkaKauppinen and Matti K. Pirkola awokemy interest in waterfowl to a morescientific direction.

During recent years, the mostimportant person for my work has beenmy excellent supervisor Hannu Pöysä.Hannu has patiently commented on mywritings (and ideas) and even though hewas very busy, he always has sent hiscomments back very quickly – on manyoccasions with the statement: I stoletime from other work and red yourmanuscript first. Hannu has encouragedme and his guidance has been invaluableduring recent years. Petri Nummi was another important person during thisprocess. He has patiently commented onall my writings. Co-operation with Petrihas always been comfortable (e.g. inwriting or planning “torpedo” duringcoffee break or with beer on a terrace).With Pentti Runko I have felt wet, chilland heat during bird ringing journeysmany times. These fine moments have

15

enormously increased my knowledge ofwetlands habitats. Pentti has collectedunique ringing data from goldeneyes andthis data has been very valuable for mythesis. Meetings of the duck group in EvoGame Research Station have been veryimportant - late hour discussions of lifeand science as well as the body andbouquet of wines with Hannu, Pentti,Petri , Markku Milonoff, Antti Paasi-vaara, Vesa Ruusila and Juha Virtanenhave been unforgettable.

I had the honour to co-operate withJukka Kauppinen, the grand old man ofwaterfowl monitoring. I began to countwaterfowl in the middle of 1980, afterreading Jukkas work in Siivekäs. Theprocess of writing and publishing ourpaper in WB (paper IV in this thesis) hasbeen very valuable and educationalexperience for me. Many people havecommented on my manuscripts andalways during the reviewing process mywritings have been improved enormously.Mikael Kilpi and Erkki Korpimäkireviewed the thesis and Alisdair Mcleanchecked the English. Matti K. Pirkola andArno Salminen brought me up on thesecrets of age and sex determination ofducks.

During study period I had many co-operators in Maaninka. My dear family:parents Eeva and Veli, my brothers Juha-Pekka and Jarmo and my late sister Anne,supported me all the time. Especially theparts played by Juha-Pekka and Rellu (aGerman fire-haired pointer) has beeninvaluable. Patiently J-P has helped meduring whole study period and withouthis field assistance a considerable part ofmy data has been impossible to collect. Inaddition, many of my friends have givena valuable field assistance for me. EsaPienmunne and Jani Pellikka has guidedme to the awe-inspiring world ofcomputers – a world of frustrating, never-

ending movements of systems. I haveworked in the Department of AppliedZoology. The spirit of our departmenthas been engaging and exhilarating.Professor Kari Heliövaara has given meexcellent opportunities to study ducks.

During last two years Kaisu Husuhas lightening my life. She has alwayssupported me - by encouraging me,giving field assistance…. This time hasbeen unforgettable for me and was alsoa crucial importance for my thesis.

I can not mention all of you. Youwho have helped me for so many years.Here I want to express my warmestgratitude to all of you. I never forgotyour support and assistance!!!

References

Andersen-Harild, P. 1981. Population dynamicsof Cygnus olor in Denmark. - Proc.Second Int. Swan Symp., Sapporo:176-190.

Anderson, D.R. 1975. Population ecology of themallard: V. Temporal and geographicestimates of survival, recovery and harvestrates. - U.S. Fish Wildl. Serv. Resour.Publ. 125.

Anderson, D.R. & Burnham, K.P. 1976.Population ecology of the mallard VI. Theeffect of exploitation on survival. - U.S.Fish Wildl. Serv. Resour. Publ. 128: 1-66.

Baines, D. 1990. The role of predation, food andagricultural practise in determining thebreeding succes of the lapving Vanellusvanellus on upland grasslands. - J. Anim.Ecol. 59: 915-929.

Bellrose, F.C. 1959. Lead poisoning as amortality factor in waterfowl. - IllinoisNatural History Survey Bulletin 27:235-288.

Bethke, R. W. & Nudds, T. 1995. Effects ofclimatical change and land use on duckabundance in Canadian prairie-parklands.– Ecological Applications 5: 588-600.

Berg, Å., Lindberg, T. & Källebrink, K.G. 1992.Hatching succes of lapwing on farmland:differences between habitats and colonies

16

of different sizes. - J. Anim. Ecol. 61: 469-476.

Boyd, H. 1964. Wildfowl and other waterfowlfound dead in England and Wales inJanuary-March 1963. - Wildfowl Trust Ann.Rep. 15: 20-23.

Burger, J. 1984. Grebes nesting in gull colonies:protective association and early warning. -Am. Nat. 123: 237-337.

Burton, J.F. 1995. Birds & climatic change. -Christopher Helm, A & C Black, London.

Caithness, T., Williams, M. & Nichols, J.D. 1991.Survival and band recovery rates ofsympatric grey ducks and mallard in theNew Zealand. - J. Wildl.Manage. 55: 111-118.

Clarke, A. L., Saether, B., E. & Roskaft, E. 1997.Sexbiases in avian dispersal: a reapprisal. -Oikos 79: 429-438.

Clausager, I. 1987. Vingeindsamling frajagtsaesonen 1986/87 i Danmark. - Raportfra Vildtbiologisk Station Landbrugsministeriets Vildtforvaltning, Juli 1987 (inDanish with English summary).

Clausager, I. 1988. Vingeindsamling frajagtsaesonen 1987/88 i Danmark. - Raportfra Vildtbiologisk Station Landbrugs -ministeriets Vildtforvaltning, Juli 1988 (inDanish with English summary).

Clausager, I. 1989. Vingeindsamling frajagtsaesonen 1988/89 i Danmark. - Raportfra Vildtbiologisk Station Landbrugsministeriets Vildtforvaltning, Juli 1989 (inDanish with English summary).

Cramp, S. and Simmons, K.E.L. (eds). 1977. TheBirds of the Western Palearctic. Vol. 1. -Clarendon Press, Oxford.

Croze, H. 1970. Searching image in CarrionCrows. - Z. Tierpsychol., Beih. 5.

Davidson, N.C. & Rothwell, P.I. 1993. Humandisturbance to waterfowl on estaries:conservation and coastal managementimplications of current knowledge. - WaderStudy Group Bulletin 68: 97-105.

Dehorter, O. & Tamisier, A. 1998. Huntingvulnerability and wintering strategy amongwaterfowl in Camargue, France. - Wildl.Biol. 4: 13-21.

Dufour, K.W. & Ankney, C.D. 1995. Huntingmortality of mallards Anas plathyrhynchosin relation to time of day, flockingbehaviour, and individual condition. - Wildl.Biol. 1: 89-96.

Eisenlohr, W.S. 1969. Hydrology of small waterareas in the prairie pothole region. Can.Wildl. Serv. Rep. Ser. 6: 35-39.

Elmberg, J., Nummi, P., Pöysä, H. & Sjöberg, K.1993. Factors affecting species numberand density of dabbling duck guild inNorth Europe. – Ecography: 16: 251-260.

Emlen, S.T. & Demong, N.J. 1975. Adaptivesignificance of synchronized breeding in acolonial birds: a new hypothesis. - ScienceN.Y. 188: 1029-1031.

Eriksson, M. O. G. 1979. Aspects of the breedingbiology of the goldeneye Bucephalaclangula. – Holarct. Ecol. 2: 186-194.

Ermala, A. 1992. Metsästysvuoden 1989/90pienriistasaalis. - Riistantutkimusosastontiedote nro 112.

Ermala, A. & Leinonen, K. 1995. Metsästäjäpro-fiili 1993/1. - Kala- ja Riistajulkaisuja 28.

Ervin, R.M. 1979. Species interactions in a mixedcolony of common terns (Sterna hirundo)and black skimmers (Rynchops niger). -Anim. Behav. 27: 1054-1062.

Evans, C.D. & Black, K.E. 1956. Duckproduction studies on the prairie potholesof South Dakota. - U.S. Fish Wildl. Serv.Spec. Sci. Rep. Wildl. 32.

Follestad, A. 1994. Innspill til en forvaltningsplanfor gjess i Norge. - Norsk Institut forNaturforskning, NINA Utredning 65: 1-78.

Forslund, P. & Larsson, K. 1992. Age-relatedreproductive success in thebarnacle goose.– J. Anim. Ecol. 61: 195-204.

Forslund, P. & Pärt, T. 1995. Age andreproduction in birds – hypotheses andtests. – Trends Ecol. Evol. 10: 373-378.

Fredga, S. & Dow, H. 1984. Factors Affectingthe Size of a Local Populations ofGoldeneye, Bucephala clangula (L.)Breeding in Sweden. – Viltrevy 13: 225-255.

Galbraith, H. 1988. Effect of agriculture on thebreeding ecology of lapwings Vanellusvanellus. - J. Appl. Ecol. 25:487-503.

Gerdes, K. & Reepmeyer, H. 1983. Zurraumlichen Verteilung ÜberwinterderSaat- und Blessgänse (Anser fabalis undAnser albifrons) in Abbängigkeit vonnaturschutzschadlichen und fordernderEinflussen. - Die Vogelwelt 104: 141-153.

Grenquist, P. 1965. Changes in abundance ofsome duck and seabird populations off thecoast of Finland 1949-1963. – FinnishGame Res. 27: 1-114.

17

Greenwood, P.J. 1980. Mating system, philopatryand dispersal on birds and mammals.Anim. Behav. 28: 1140-1162.

Götmark, F. 1989. Costs and benefits to Eidersnesting in gull colonies: a field experiment. -Ornis Scand. 20: 283-288.

Götmark, F. & Andersson, M. 1980. Breedingassociation between Common Gull Laruscanus and Arctic Skua Stercorariusparasiticus. - Ornis Scand. 11: 121-124.

Götmark, F. & Åhlund, M. 1988. Nest predationand nest site selection among EidersSomateria mollissima: the influence ofgulls. - Ibis 130: 111-123.

Hagemeijer, E.J.M. and Blair, M.J. (toim.) 1997.The EBCC Atlas of European BreedingBirds; Their distribution and abundance. - T& A D Poyser, London.

Heitmeyer, M.E., Fredrickson, L.H. & Humburg,D.D. 1993. Further evidence of biasesassociated with hunter killed mallards. - J.Wildl. Manage. 57: 733-740.

Hepp, G.R., Blohm, R.J., Reynolds, R.E., Hines,J.E. & Nichols, J.D. 1986. Physiologicalcondition of autumn banded mallards and itsrelationship to hunting vulnerability. - J.Wildl. Manage. 50: 177-183.

Hildén, O. 1964. Ecology of duck populations inthe island group of Valassaaret, Gulf ofBothnia. - Ann. Zool. Fenn. 1: 153-279.

Hildén, O. 1966. Changes in the bird fauna ofValassaaret, Gulf of Botnia, during recentdecades. – Ann. Zool. Fenn. 3: 245-269.

Johnson, D.H., Nichols, J.D. & Scwartz, M. D.1992. Population dynamics of breedingwaterfowl. - In: Batt, B.D.J., Afton, A.D.,Anderson, M.G., Ankney, C.D., Jonson,D.H., Kadler, J.A. and Krapu, G.L. (eds):Ecology and management of breedingwaterfowl. Univ. Minn. Press, Minnespolis,pp. 446-485.

Kalela, O. 1946. Zur Ausbreitungsgeschichte derVögel vegetationsreicher Seen. – Ann.Acad. Sci. Fenn., Ser. A, IV. Biol. 12: 1-81.Kalela, O. 1949. Changes in geographicalranges in the avifauna of northern andcentral Europe in relation to recent changesin climate. - Bird Banding 20: 77-103.

Kauppinen J. 1993. Densities and habitatdistribution of breeding waterfowl in boreallakes. - Finnish Game Res. 48: 24-45.

Kauppinen, J. 1995. Temporal variation in thewetland waterfowl communities of theFinnish lake district. - Ornis Fennica 72:145-153.

Kauppinen, J. 1997. Structure of BreedingWaterfowl Communities in Boreal lakes.An approach to Monitoring WaterfowlCommunities. - Kuopio UniversityPublications C. Natural and EnviromentalScience 59.

Kauppinen, J. & Väisänen, R.A. 1993.Ordination and classification of waterfowlcommunities in south boreal lakes. –Finnish Game Res. 48: 3-23.

Kokko, H. & Linsdtröm, J. 1998. Seasonaldensity depence, timing of mortality, andsustainable harvesting. - Ecol. Model. 110:293-304.

Kokko, H., Pöysä, H., Lindström, J. & Ranta, E.1998. Assessing the impact of springhunting on waterfowl populations. – Ann.Zool. Fenn. 35: 195-204.

Krebs, J.,R. 1974. Colonial nesting and socialfeeding as strategies for exploiting foodresources in the great blue heron (Ardeaherodias). - Behaviour 51: 99-134.

Krements, D.G., Conroy, M.J., Hines, J.E. &Percival, H.F. 1987. Sources of variationin survival and recovery rates of Americanblack ducks. - J. Wildl. Manage. 51: 689-700.

Lack, D. 1968. Ecological adaptations forbreeding in birds. - Methuen, London.

Landry, P. 1990. Hunting harvest of waterfowl inthe Western palearctic and Africa. – In:Mattehevs, G., V., T. (eds): Monitoringwaterfowl populations. IWRB SpecialPublications 12, Slimbridge, UnitedKingdom.

Larsen, T. & Molsvor, J. 1992. Antipredatorbehavior and breeding association of Bar-tailed Godwits and Whimbrels. - Auk 109:601-608.

Larsen, T. & Grundetjern, S. 1997. Optimalchoice of neighbour: predator protectionamong tundra birds. - J. Avian Biol. 28:303-308.

Leitch, W.G. & Kaminski, R.M. 1985.Long-term wetland-waterfowl trends inSaskatchewan grassland. - J. Wildl.Manage. 49: 212-222.

Lima , S.L.& Dill, L.M. 1990. Behavioraldecisions made under the risk of predation:a review and prospectus – Can. J. Zool. 68:619-640.

Lorentsen, O. 1988. Tidlig jakt på grågås.Erfaringen fra forsök på Smöla 1982-1984.- DN-raport 5. Norsk Direktorat forNaturforvaltning, 15 pp.

18

Madsen, J. 1985. Impact of disturbance on fieldutilization of Pink-footed Geese in WestJutland, Denmark. – Biological Conser-vation 33: 53-63.

Madsen, J. 1998a. Experimental refuges formigratory waterfowl in danish wetlands -II-tests of hunting disturbance effects. - J.Appl. Ecol. 35: 398-417.

Madsen, J. 1998b. Experimental refuges formigratory waterfowl in danish wetlands -I-baseline assessment of the disturbanceeffects of recreational. - J. Appl. Ecol. 35:386-397.

Madsen, J. & Jepsen, P.U. 1992. Passing the buck.Need for a flyway management plan for theSvalbard Pink-footed Goose. - In vanRoomen, M. & Madsen, J. (eds): Waterfowland agriculture: review and futureperspective of the crop damage conflict inEurope. IWRB Special Publications No. 21,Slimbridge, UK, pp. 109-110.

Madsen, J. & Fox, A.D. 1995. Impacts of huntingdisturbance on waterbirds - a review. -Wildl. Biol. 1: 193-207.

Madsen, J. & Fox, A.D. 1997. The impact ofhunting disturbance on waterfowlpopulations - the consept on flyway networkof disturbance free areas. - Gibier FauneSauvage, Game Wildlife, Vol. 14 (2): 201-209.

Madsen, J., Pihl, S. & Clausen, P. 1998.Establishing a reserve network forwaterfowl in Denmark: a biologicalevaluation of needs and consequences. -Biological Conservation 85: 241-255.

Martin, T.E. 1993. Nest predation amongvegetation layers and habitat types revisingthe dogmas. - Am. Nat. 141: 897-913.

Mauser, D.M., Jarvis, R.L. & Gilmer, D.S. 1994.Survival of radio-marked mallard ducklingsin northeastern California. - J. Wildl.Manage. 58: 82-87.

Mayhew, P. 1988. The daily energy intake ofEuropean Wigeon in winter. – Ornis Scand.19: 217-223.

McGowan, J.D. 1975. Effects of autumn andspring hunting on Ptarmican populationtrends. - J. Wildl. Manage. 39: 491-495.

Merilä, E., Ojanen, M. & Orell, M. 1977. Oulunseudun sorsien rengastusajoista ja löydöistä.- Aureola 2: 61-72.

Metz, K.J. & Ankney, C.D. 1991. Are brightlycoloured male ducks selectively shot byduck hunters? - Can. J. Zool. 69: 279-282.

Mihelsons, H., Mednis, A. & Blums, P. 1986.Population ecology of migratory ducks inLatvia. - "Zinatne". Riga.

Milonoff, M. 1998. Clutch size determination inprecocial birds with self-feeding chicks. –Unpubl. doctoral thesis. Helsinki

Milonoff, M. Pöysä, H. & Runko, P. 1998.Factors affecting clutch size and ducklingsurvival in the common goldeneyeBucephala clangula. - Wildl. Biol. 4: 73-80.

Monval, J-Y. & Pirot, J-Y. 1989. Results of theIWRB Interna-tional Waterfowl Census1967-1986. - IWRB Spec. Publ. 8: 1-145.

Newton, I. 1998. Population limitation in birds. -Academic press, London.

Newton, I. and Campbell, R.G. 1975. Breedingof ducks at Loch Leven, Kinross. –Wildfowl 26: 83-103.

Nichols, J.D., Conroy, M.J., Anderson, D.R. &Bunham, K.P. 1984. Compensatorymortality in waterfowl populations: areview of the evidence and implicationsfor research and management. - Trans. N.Amer. Wildl. Nat. Res. Conf. 49: 535-553.

Nichols, J.D., Williams, M. & Caithness, T.1990. Survival and band recovery rates ofmallards in New Zealand. - J. Wildl.Manage. 54: 629-636.

Nilsson, L. 1979. Variation in the production ofyoung of swans wintering in Sweden. -Wildfowl 30: 129-134.

Nilsson, L. 1984. The impact of hard winters onwaterfowl populations of south Sweden. -Wildfowl 35: 71-80.

Norrdahl, K., Suhonen, J., Hemminki, O. andKorpimäki, E. 1995. Predator presencemay benefit: Kestrels protect curlew nestsagainst nest predation. - Oecologia 101:105-109.

Nudds, T. D. 1992. Patterns in breeding duckcommunities. – In: Batt, B. D. J., Afton, A.D., Anderson, M. G, Ankney, C. D.,Johnson, D. H., Kadlec, J. A. & Krapu, G.J. (eds). Ecology and management ofbreeding waterfowl. University ofMinnesota Press, Minneapolis. pp. 540-567.

Nudds, T. D. & Bowlby, J. N. 1984. Predator-prey size relationships in North Americandabbling ducks. - Can. J. Zool. 62: 2002-2008.

Nudds, T. J., Sjöberg, K. & Lundberg, P. 1994.Ecomorphological relationships amongPalearctic dabbling ducks on Baltic coastal

19

wetlands and a comparison with theNearctic. - Oikos 69: 295-303.

Nudds, T. D., Elmberg, J., Pöysä, H., Sjöberg, K.& Nummi, P. 2000. Ecomorphology inbreeding holarctic dabbling ducks: theimportance of lamellar density and bodylenght varies with the shape of wetlandbasins and the complexity of vegetation. –Oikos 91: 583-588.

Nuechterlein 1981. "Information parasitism" inmixed colonies of western grebes andfoster's terns. - Anim. Behav. 29:985-989.

Nummi, P. 1993. Food niche relationships ofsympatric mallard and green-winged teal. -Can. J. Zool. 71: 49-55.

Nummi, P. & Pöysä, H. 1993. Habitat associationof ducks during different phases of thebreeding season. - Ecography 16: 319-328.

Nummi, P., Elmberg, J. , Pöysä, H. & Sjöberg, K1995. Occurrence and density of mallardand green-winged teal in relation to preysize distribution and food abundance. –Ann. Zool. Fenn. 32: 385-390.

Nummi, P. & Pöysä, H. 1997. Brood production ofducks in southern Finland. – Suomen Riista43: 65-71 (In Finnish with Englishsummary).

Nummi, P., Sjöberg, K., Pöysä, H. & Elmberg, J.2000. Individual foraging behaviourindicates resource limitation: anexperiment with mallard ducklings. – Can.J. Zool. 78: 1891-1896.

Olson, D.P. 1964. Differential vulnerability ofmale and female canvasbacks to hunting. -Trans. N. Amer. Wildl Nat. Res. Conf. 30:121-135.

Orthmeyer, D.L. & Ball, I.J. 1990. Survival ofmallard broods on Benton lake NationalWildlife Refuge in northcentral Montana. -J. Wildl. Manage. 54: 62-66.

Owen, M. and Black, J. M. 1990. Waterfowlecology. - Chapman & Hall. New York .

Owen, M. & Williams, G. 1976. Winterdistribution and habitat requirements ofWigeon in Britain. - Wildfowl 27: 83-90.

Owens, N.W. 1977. Responses of wintering BrentGeese to human disturbance. - Wildfowl 28:5-14.

Patterson, O. 1979. Experiences in Canada. -Trans. N. Amer. Wildl. Nat. Res. Conf. 44:130-139.

Pirkola, M.K. & Lindén, H. 1972. Results of duckwing collection surveys in Finland 1969 and1970. - Suomen Riista 24: 97-106 (inFinnish with English summary).

Pius, S.M. & Leberg, P.L. 1998. The protectorspecies hypothesis: Do black skimmersfind refuge from predators in gull billedtern colonies? - Ethology 104: 273-284.

Posphala, R.S., Anders, D.R. & Henny, C.J.1974. Breeding habitat conditions, size ofthe breeding populations, and productionindices. - U.S. Fish Wildl. Serv. Resour.Publ. 115.

Putaala, A. & Hissa, R. 1993. Mortality andreproduction of wild and hand-reared greypartridge in Tyrnävä, Finland. - SuomenRiista 39: 41-52 (In Finnish with Englishsummary).

Pöysä, H. 1983a. Resource utilization patternand guild structure in a waterfowlcommunity. – Oikos 40: 295-307.

Pöysä, H. 1983b. Morphology-mediated nicheorganisation in the guild of dabblingducks. – Ornis Scand. 14: 317-326.

Pöysä, H. 1987. Ecology and foragingbehaviour in dabbling ducks (Anas spp.).– University of Joensuu, PublicationSeries No. 10.

Pöysä, H. 1988. Do foraging teals exploit gullsas early warners? - Orn. Scand. 19: 71-72.

Pöysä, H. 1989. Geographical gradients in thestability of waterfowl communities inFinland. - Suomen Riista 35: 7-16 (inFinnish with English summary).

Pöysä, H. 1999. Conspesific nest parasitism isassociated with inequality in nest predationrisk in the common goldeneye (Bucephalaclangula). – Behav. Ecol. 10: 533-540.

Pöysä, H., Elmberg, J., Nummi, P. & Sjöberg, K.1994. Species composition of dabblingduck assemblages: Ecomorphologicalpatterns compared with null models. -Oecologia 98: 193-200.

Pöysä, H. & Virtanen, J. 1994. Habitat selectionand survival of common goldeneye(Bucephala clangula) broods -preliminary results. - Hydrobiologia 279:280-296.

Pöysä, H., Elmberg, J., Nummi, P. & Sjöberg,K 1996. Are ecomorphologicalassociations among dabbling ducksconsistent at different spatial scales? –Oikos 76: 608-612.

Pöysä, H., Runko, P. & Ruusila, V. 1997. Natalphilopatry and the local resourcecompetition hypothesis: data from thecommon goldeneye. - J. Avian Biol. 28:63-67.

20

Reinecker, W.C. 1976. Distribution, harvest andsurvival of American wigeon banded inKalifornia. - California Fish and GameJournal 62: 141-153.

Reinecke, K.J. & Shaiffer, C.W. 1988. A field testfor differences in condition among trappedand shot mallards. - J. Wildl. Manage. 52:227-232.

Reynolds, R. E. & Sauer, J. R. 1991. Changes inmallard breeding populations in relation toproduction and harvest rates. - J. Wildl.Manage. 55: 483-487.

Ricklefs, R.E. 1969. An analysis of nestingmortality in birds. - Smithson. Contrib. Zool.9: 1-48.

Rohwer, F., C. 1992. The evolution of reproductivepatterns in waterfowl. - In: Batt, B.D.J.,Afton, A.D., Anderson, M.G., Ankney,C.D., Jonson, D.H., Kadler, J.A. and Krapu,G.L. (eds): Ecology and management ofbreeding waterfowl. Univ. Minn. Press,Minnespolis, pp. 486-539.

Rogers, J.P., Nichols, J.D., Martin. F.W., Kimball,C.F. & Pospahala, R.S. 1979. Anexamination of harvest and survival rates ofducks in relation to hunting. - Trans. N.Amer. Wildl. Nat. Res. Conf. 44: 114-126.

Rose, P. M. & Scott, D.A. 1997. WaterfowlPopulation Estimates. – WetlandsInternational Publication 44.

Rosenberg, K. V., Ohmart, R. D. & Anderson, B.W. 1982. Comminity organization ofriparian breeding birds: response to anannual resource peak. - Auk 99: 260-273.

Rotenberry, J. T. 1980. Dietary relationshipsamong shrubsteppe passerine birds:competition or opportunism in a variableenvironment? - Ecol. Monographs 50: 93-110.

Ruokolainen, K., Kauppinen, J. & Väänänen, V.-M. 1999. Naurulokki. - In: Ruokolainen, K.& Kauppinen, J. (eds): Kuopion ja Pohjois-Savon linnusto. – Kuopionluonnontieteellisen museon julkaisuja 5.

Ruusila, V. 1999: Maternal investment, femalephilopatry and reproductive success in thecommon goldeneye Bucephala clangula. –Annales Universitatis Turkuensis ser. AII,Tom. 129.

Ruusila, V., Pöysä, H. & Runko, P. 2000.Characteristics of maternal family lineagesin a Common Goldeneye Bucephalaclangula breeding population. – Ornis Fenn.77: 77-82.

Salminen, A. 1983. Suomen sorsalinnut. - SLY:nLintutieto Oy, Helsinki.

Sargeant, A.B. and Raveling, D.G. 1992.Mortality during breeding season. - In:Batt, B.D.J., Afton, A.D., Anderson,M.G., Ankney, C.D., Jonson, D.H.,Kadler, J.A. and Krapu, G.L. (eds):Ecology and management of breedingwaterfowl. Univ. Minn. Press,Minnespolis, pp. 396-422.

Sæther, B.-E. 1990. Age-spesific variation inreproductive performance of birds. – Curr.Ornithol. 7: 251-283.

Savard, J.-P., Smith, G.E.J. & Smith J.N.M.1991. Duckling mortality in Barrow'sgoldeneye and bufflehead broods. - Auk108: 568-577.

Schoener, T. W. 1986. Resource partitioning. –In: Kikkawa, J. & Anderson, D. J.. (eds.) :Community Ecology. Pattern and Process.Blackwell Sci. Publ. Oxford. pp. 91-126

Scott, D.A. 1982. Problems in the managementof waterfowl populations. - In: Scott, D.A.& Smart, M. (eds): Proceedings 2ndTechnical Meeting on Western PalearcticMigratory Bird Management, Paris, 1979.Slimbridge, IWRB, 89-106.

Sheeley, D.G. & Smith, L.M. 1989. Test of dietand condition bias in hunter-killednorthern pintail. - J.,Wildl. Manage. 53:765-769.

Sjöberg, K., Pöysä, H., Elmberg, J. & Nummi, P.2000. Response of mallard ducklings tovariation in habitat quality: an experimentof food limitation. – Ecology: 329-335.

Siira, J. & Eskelinen, O. 1983. Changes in theabundance of breeding waterfowl in theLiminka bay in 1954-81. - Finnish GameRes. 40: 106-121.

Smith, J. N. M., Grant, P. R., Grant, B. R., Abbot,I. J. & Abbot, L. K. 1978. Seasonalvariation in feeding habits of Darwin'sground finches. - Ecology 59: 1137-115.

Stoudt, I.J. & Cornwell, G.W. 1976. Non-huntingmortality of fledged North Americanwaterfowl.- J. Wildl. Manage. 40: 681-691.

Summers, R. W. & Underhill, L. G. 1987. Factorrelated breeding production of Brent GeeseBrant bernicla and waders (Charadrii) onthe Taimyr Pennisula. – Bird Study 33:105-108.

Suomen Virallinen Tilasto 1997. Riistasaalismetsästysvuonna 1994/95. –SVT.

21

Ympäristö 1997: 5. Riista- ja kalataloudentutkimuslaitos, Helsinki.

Suomen Virallinen Tilasto 2000. Riistasaalismetsästysvuonna 1999. –SVT. Maa-,metsä- ja kalatalous 2000:9. Riista- jakalatalouden tutkimuslaitos, Helsinki

Sutherland, J.M. 1991. Effects of drought onAmerican coot (Fulica americana)reproduction in Saskatchewan parklands. -Can. Field Nat. 105:267-273.

Swanson, G. A. & Bartonek, J. C. 1970. Biasassociated with food analyses in gizzards ofblue-winged teal. - J. Wildl. Manage. 34:739-746.

Talent, G.L., Jarvis, R.L. & Krapu, G.I. 1983.Survival of mallard broods in south-centralNorth Dakota. - Condor 85: 74-78.

Tinbergen, N., Impekoven, M. & Franck, D. 1967.An experiment on spacing out as a defenceagainst predators. – Behaviour 28: 307-321.

Valkama, J., Currie, D. & Korpimäki, E. 1999.Differences in the intensity of nest predationin the curlew Numenius arquata: Aconsequence of land use and predatordensities? – Ecoscience 6: 497-504.

Valle, R. & Scarton, F. 1999. The presence ofconspicuous associations protects nestingRedhank Tringa totanus from aerialpredators. – Ornis Fenn. 76: 145-149.

Viksne, J. 1997. The bird lake Engure. - Jana setapublishers & Printers Ltd.

Virtanen, J., Väänänen, V.-M., Nummi, P.,Jauhiainen, T. & Pienmunne, E. 1998. Acomparison of the survival of tranlocatedwild and hand-rered pheasant hens. -Suomen Riista 44: 30-36 (in Finnish withEnglish summary)

von Haartman, L. 1945. Zur Biologie der Wasser-und Ufervögel im SchärenmeerSudwestfinnlands. - Acta Zool. Fenn. 44: 1-120.

von Haartman, L. 1957. Population changes in thetufted duck, Aythya fulicula, (L.). – SociatasScientiarum Fennica CommentationesBiologicae 16, 5: 1-11.

von Haartman, L. 1973. Changes in the breedingbird fauna of the north Europe. – In: Farner,D.S. (ed.): Breeding Biology of Birds.National Academy of Sciences, Washington,pp. 448-481.

Väisänen, R.A., Lammi, E. & Koskimies, P. 1998(eds). Muuttuva pesimälinnusto. – Otava.

Väänänen, V.-M. 1992. Metsästyspaineenvoimakkuudesta ja vaikutuksistavesilintukantoihin Pohjois-Savossa. –

Unpubl. M. Sc thesis, University ofHelsinki.

Väänänen, V.-M. 1996. Hunting pressure ofducks in Finland according to ringing data.- Suomen Riista 42: 40-46 (in Finnish withEnglish summary).

Väänänen, V.-M. 1999. Vesilinnut kansainvälisinriistavaramme. - Riistantutkimuksentiedote nro 156: 3-4.

Väänänen, V.-M. 2000. Vesilintujenmetsästysverotus. – In: Nummi, P. &Väänänen, V.-M. (eds): Riistanhoito,Metsälehti Kustannus, Hämeenlinna, pp132-145.

Ward, P. & Zahavi, A. 1973. The importance ofcertain assemblages of birds as“information centres” for food findings. -Ibis 115: 517-534.

Weatherhead, P.J. & Ankney, C.D. 1984. Acritical assumption of band-recoverymodels may often be violated. - Wildl.Soc. Bull. 12: 198-199.

Wiens, J.A. 1989. The ecology of birdcommunities, Vol 2: Processes andvariations. - Cambridge University press,Cambrige.

Wiens, J. A. 1993. Fat times, lean times andcompetition among predators. - TrendsEcol. Evol. 8: 348-349.

Wiklund, C.G. 1982. Fieldfare Turdus pilariabreeding succes in relation to colony size,nest position and association with merlinsFalco columbarius. - Behav. Ecol.Sociobiol. 11: 165-172.

Yarker, B. & Atkinson-Willes, G.L. 1971. Thenumerical distribution of some Britishbreeding ducks. - Wildfowl 22: 63-70.