Bucephala Clangula Research Articles

Plasticity in timing of avian breeding in response to spring temperature differs between early and late nesting species

Plasticity for breeding dates may influence population vulnerability to climate change via phenological mismatch between an organism’s life cycle requirements and resource availability in occupied environments. Some life history traits may constrain plasticity, however there have been remarkably few comparisons of how closely-related species, differing in key traits, respond to common phenology gradients. We compared population- and individual-level plasticity in clutch initiation dates (CID) in response to spring temperature among five duck species with early- to late-season nesting life histories. Plasticity was strongest in females of the earliest breeding species (common goldeneye [Bucephala clangula], mallard [Anas platyrhynchos], and gadwall [Mareca strepera]), whereas late-nesting lesser scaup (Aythya affinis) and white-winged scoter (Melanitta fusca deglandi) did not respond. These results contrast with previous work in other bird families that suggested late-breeders are generally more flexible. Nevertheless, late-breeding species exhibited annual variation in mean CID, suggesting response to other environmental factors unrelated to spring temperature. Goldeneye and gadwall females varied in their strength of individual plasticity (‘individual × environment’ interactions) and goldeneye and scoter females showed evidence of interannual repeatability of CID. Fitness consequences of CID plasticity in response to spring phenology, including trophic mechanisms and population consequences, warrant investigation.

High site fidelity does not equate to population genetic structure for common goldeneye and Barrow's goldeneye in North America

Delineation of population structure provides valuable information for conservation and management of species, as levels of demographic and genetic connectivity not only affect population dynamics but also have important implications for adaptability and resiliency of populations and species. Here, we measure population genetic structure and connectivity across the ranges of two sister species of sea ducks: Barrow's goldeneye Bucephala islandica and common goldeneye B. clangula. We use two different marker types: 7–8 nuclear microsatellite loci assayed across 229 samples and 3678 double digest restriction‐site associated DNA sequencing (ddRAD‐seq) loci assayed across 61 samples. First, both datasets found no evidence of genetic structure within common or Barrow's goldeneye, including between North American and European samples of common goldeneye. These results are in contrast with previous mitochondrial DNA, band recovery and telemetry data which suggest that goldeneyes are structured across their range. We posit that the discordance between autosomal genetic markers and other data types suggests that males, possibly subadult males, may be maintaining genetic connectivity across each species' respective ranges. Next, although mate choice consequences resulting from inter‐specific brood parasitism was hypothesized to cause some level of gene flow between goldeneye species, we only identified a single F1 hybrid with no further evidence of contemporary or historical gene flow. Despite ddRAD‐seq demographic analyses which recovered an optimum evolutionary model of split‐with‐migration (i.e. secondary contact), estimates of gene flow were <<1 migrant per generation in both directions. Together, we conclude that either strong ecological barriers or assortative mating are likely playing a role in preventing further backcrossing. Finally, demographic analyses estimated a relatively deep divergence time between Barrow's goldeneye and common goldeneye of ~1.6 million years before present and suggests that the genomes of both species have been under similar evolutionary constraints.

Changes in numbers and distribution of wintering waterbirds at the south coast of Scania, Sweden, during 55 winters, 1964–2018

The south coast of Scania, southernmost Sweden, has long been an important wintering and staging area for waterbirds. A large part of the coast was surveyed annually as a part of the international midwinter counts for 55 years (1964–2018). The total number of wintering waterbirds showed an increasing trend but there was much variation between years. Common Goldeneye Bucephala clangula, followed by Mallard Anas platyrhynchos, Tufted Duck Aythya fuligula and—during the early years—Long-tailed Duck Clangula hyemalis, dominated the community. Great Cormorant Phalacrocorax carbo, Mallard, Common Goldeneye and Eurasian Coot Fulica atra increased in numbers, reflecting the national and international trends related to milder winters and a northward shift of the winter distribution. Eurasian Wigeon Mareca penelope and Great Crested Grebe Podiceps cristatus established wintering traditions in the area during the study period. Tufted Duck and Common Merganser Mergus merganser decreased locally due to a northward shift of the wintering distribution northwards within the country. The Long-tailed Duck was an important winter guest in the first years but was only seen in very small numbers in later years, reflecting the general and large-scale decrease of the Baltic wintering population.

Use of Tree Cavities and Nest Boxes by Wood Ducks at Missisquoi National Wildlife Refuge

We measured use rates, nest success, and inter- and intra- specific nest parasitism by ducks using tree cavities and nest boxes in an old-growth forested floodplain at Missisquoi National Wildlife Refuge in Swanton, VT. Our study represents a previously under-explored opportunity to evaluate various breeding-season characteristics for ducks using both natural and artificial nest cavities in the same forested stand in the northeastern US. Overall use (72.5% vs. 14.5%) and nest-success rates (48.3% vs. 0.0%) were greater in artificial nest boxes but so was nest parasitism (62.1% vs. 0.0%). In addition, Aix sponsa (Wood Duck) were the only species using artificial nest boxes consistently even though this region represents a rare location in North America where they coexist with Lophodytes cucullatus (Hooded Merganser) and Bucephala clangula (Common Goldeneye), which are also cavity-nesting obligates. We found many (n = 35) unused available tree cavities over 2 years, and thus it is unlikely nest site availability is a limiting factor for population growth of cavity nesting ducks at Missisquoi NWR. Future research efforts should try to determine the factors affecting nest-cavity selection.

An account of a first record of the Common Goldeneye Bucephala clangula Linnaeus, 1758 (Aves: Anseriformes: Anatidae) in Bhutan

PunatsangChhu in Wangduephodrang 27.486°N 89.899°E (1,273m) is one of the largest rivers and an important zone in Bhutan for resident and migrant water birds. It is the expanse where the diverse birds are seen on a stretch between 27.462°N 89.901°E and 27.579°N 89.867°E (Tobgay 2017). Large numbers of winter migratory water birds in Bhutan have been found in this location (Spierenburg 2005). Common Goldeneye Bucephala clangula was first sighted on Saturday, 5th of January, 2019 along PunatsangChhu 27.512657’N 89.887610’E at the elevation of 1142meter above sea level in the morning but couldn’t capture photo and more over mistreated it to be some other common water birds. However, until on 8th of January, 2019, it was a success to have photographed while it was foraging alone at the sand extraction sites at around 12:30 hours in the evening. The duck was observed diving simultaneously under water foraging at the time of sighting. It was then photographed with the help of DSLR camera and kit lens 55–300 mm until it flew away to other side of the river.

Bird images in the mosaics of Late Antique basilicas in the town of Sandanski (Blagoevgrad Region, SW Bulgaria)

This paper presents and analyses for the first time all data on bird images of two Late Antique basilicas of the Roman period (5th-6th c. AD) in the town of Sandanski (SW Bulgaria). A total of eight species have been recognised on the floor mosaics of both basilicas: Anas platyrhynchos, Bucephala clangula, Dendrocygna viduata, Nettapus coromandelianus, Marmaronetta angustirostris, Porphyrio porphyrio, Psittacula krameri, and Sypheotides indicus. Exotic birds of Palaeotropic (Ethiopian) and Indomalayan (Oriental) distribution confirm once again the active ancient Roman contacts with East and Trans-Saharan Africa and the Hindustan Peninsula.

МІГРАЦІЙНІ СКУПЧЕННЯ ВОДОПЛАВНИХ І НАВКОЛОВОДНИХПТАХІВ У ЦЕНТРАЛЬНІЙ ЧАСТИНІ КРЕМЕНЧУЦЬКОГО ВОДОСХОВИЩА В ОСІННІ ПЕРІОДИ 2015–2017 РР.

Introduction. Kremenchuk Reservoir plays an important part in maintaining populations of waterfowl and waterbirds in the migration period. They stop to rest and feed here. The upper part of the Reservoir is promising for inclusion in the Ramsar list. A significant part of this area is occupied by the Lypivsky Ornithological Reserve with a total area of 4631 hectares. We have been monitoring waterfowl and waterbirds around the reserve for over 20 years. The purpose of the study is to establish the species composition and relative number of waterfowl and waterbirds in the central part of the Kremenchuk Reservoir, to study their seasonal and long-term dynamics. Methods. The records cover the central part of the Kremenchuk Reservoir: along the right bank - within the city of Cherkasy, along the left one - from the village Kedyna Hora to the village of Blagodatne (former village of Chapaiivka) (Zolotonosha district of Cherkasy region), as well as along the dam that crosses the Reservoir. The study was conducted by the point count method from the shore and the dam. 17 records were conducted during autumn periods of 2015-2017. Results. In total for three years, we have found 44 species belonging to 8 series. The core of the avifauna consisted of Mallard (Anas plathyrhynchos), Coot (Fulica atra), the Tufted Duck (Aythya fuligula) and Great Cormorant (Phalacrocorax carbo) making 82.3% - 86.1% of the total number of birds in different years. The Shannon species diversity index in 2015 were 1 . 50-2 . 61 , in 2016 – 1 . 17-1 . 97 , in 2017 – 1 . 37-2 . 72 . The maximum number of birds stopping to rest and feed during a season in the central part of the Kremenchuk Reservoir was from about 13,600 up to about 29,500 birds in different years. During 2015-2017, among the mass species for three ones (Great Crested Grebe (Podiceps cristatus), the Tufted Duck and the Black-headed Gull (Larus ridibundus)), there was the highest number for more than 20 years of the research. 6 species listed in the Red Book of Ukraine were identified. Among them, the studied area plays a significant role in maintaining the populations of the Common Goldeneye (Bucephala clangula) and White-Tailed Eagle (Haliaeetus albicilla). Originality. The n umber and bird diversity of the ornithocomplex due to climate change has been described. The number of some numerous species is increasing compared to previous years . Conclusion. The results of the research confirm the importance of the Lypivsky Ornithological Reserve, where more birds than in the surrounding areas, are concentrated. Such preferences are associated with more attractive conditions for feeding and resting of mass species.

CHARACTERISTICS OF VISIBLE AUTUMN MIGRATIONS OF WATERFOWL IN NATIONAL PARK «PRYPIAT-STOKHID» IN 2012-2017

CHARACTERISTICS OF VISIBLE AUTUMN MIGRATIONS OF WATERFOWL IN NATIONAL PARK «PRYPIAT-STOKHID» IN 2012-2017

Water body type and group size affect the flight initiation distance of European waterbirds.

Human encroachment on nature grows constantly, increasing human-wildlife interactions. Flight initiation distance (FID, the distance at which animals flee from an approaching threat) is often used to measure antipredator behaviour and establish buffer zones to reduce human impact on wildlife. In this study, we approached 10 waterbird species on larger lakes and narrower rivers using a motorboat. We investigated whether water body type, season (winter/spring), approach starting distance, species body mass, and group size influenced bird FID. Average bird FID was 145 ± 92 m and differed between species. In general, FID of all species was larger on lakes than rivers and increased with increasing group size and approach starting distance. When analysed separately for the two most common species, common goldeneyes (Bucephala clangula) and mallards (Anas platyrhynchos), FID increased with increasing starting distance on rivers, but not lakes, likely because birds on lakes have enough time to evaluate the approaching object and take flight at great distance. Additionally, birds might perform different activities on lakes versus rivers, leading to varying energetic trade-offs between the two habitat types, which may affect the decision when to take flight. Finally, mallards aggregated in larger groups on lakes, which affected FID, likely due to enhanced visibility (i.e., earlier detection of the approaching boat) and detection probability (via increased group size) on lakes. Our results emphasize the importance of accounting for habitat characteristics, such as water body type, when studying waterbird FID, because they can affect the visibility of stimuli, group size and potentially animal behaviour, factors which should be taken into account when planning buffer zones for waterbirds in conservation areas.

Morphological and ecological characteristic of Dicranotaenia stenosacculata Macko, 1988 (Cestoda, Hymenolepididae) recorded in Poland

During the parasitological examination of 288 wild ducks from north-western Poland, 18 tapeworms were found in the intestines (jejunum, ileum and rectum) of six birds, which, based on the structure of the scolex, internal organs and the presence of cirrus with an internal additional sac, were determinated as Dicranotaenia stenosacculata Macko, 1988. Tapeworms were found in two young females Bucephala clangula, one young female Aythya marila as well as two adult males Aythya fuligula. The aim of the study was to present the morphological and ecological characteristics of the species, recently discovered for the first time in the fauna of Poland.

Current condition of the ornithofauna of the Alexandria Dendrological Park

The species composition of birds of the Alexandria Dendrological Park has been analyzed. The studies were conducted in 2008–2018. In total 148 bird species were registered (35% of the ornithofauna of Ukraine). Birds were analyzed by biotopic groups, nature of stay and type of nesting. It was found that in the conditions of the Alexandria Dendrological Park, the dominant ecological groups were dendrophiles (80 species). According to the nature of their stay, nesting birds accounted for 90 species, migratory – 48 species, wintering – 31 species. Depending on the type of nesting, canopy-nesting and hole-nesting birds prevailed – 27.8 and 24.4% respectively. Representatives of Piciformes and Passeriformes make up a significant part of the nesting species, which is 10 and 57.8% respectively. Falconiformes are represented by 4 species, which is 4.4% of the total number of nesting species. The value of the park also consists in the presence of favorable wetlands for wintering and forage migration of a number of taxon birds in its territory. As a result, the bird population is growing. The emergence of new bird species in recent years can provide a unique indication of the importance of ornithocenosis in these areas. This concerns in particular Green Woodpecker, Black kite, Honey Buzzard, Night Heron, Stock Dove, Spotted Crake. It has been established that new species appear in the park, settling from nearby or remote areas. During the years of observation, 9 species from the Red Data Book of Ukraine (Ciconia nigra, Netta rufina, Haliaeetus albicilla, Milvus migrans, Buteo rufinus, Pandion haliaetus, Bucephala clangula, Picus viridis, Columba oenas) have been recorded. The factors influencing the species composition of birds have been analyzed. They include felling of trees, thinning of shrubs, uncontrolled recreation and direct predation from dogs. One of the main problems limiting the number of birds in the park is trespassing of logging processes, in particular during the nesting period. In the future, more comprehensive studies are planned on the quantitative composition of birds, as well as features of the topical distribution according to the biocenosis.

Associations between duck harvest, hunting wing ratios and measures of reproductive output in Northern Europe

Ducks are important game species, hunted in several countries throughout their annual cycle. We investigated whether the size of the annual duck harvest in Finland and Denmark reflected annual reproductive output in three common quarry duck species. Finland represents an important breeding area and Denmark important staging/wintering grounds for common teal (Anas crecca), Eurasian wigeon (Mareca penelope) and common goldeneye (Bucephala clangula). We assessed whether (i) annual duck harvest in these two countries correlated with variation in Finnish reproductive output or adult population size during 1990–2016 and (ii) variation in reproductive output of Finnish ducks was reflected in the juvenile ratios of birds harvested in Finland (2005–2007, 2014–2016) or Denmark (1990–2016). We hypothesised that variation in Finnish reproductive output would positively affect the size and juvenile ratio of the harvest, and that this effect would be stronger closer to the breeding grounds. Our data showed that the annual harvest of goldeneye in Finland was positively correlated with reproductive output, a desirable basis for applying sustainable management to this species. Teal and wigeon have much longer, more complex flyways, and their harvest did not mirror the annual production of young, although the wigeon harvest in Denmark increased with increasing juvenile ratio there. For these populations, we need to better define population units if we are to be able to assess harvest sustainability. We urgently need to monitor duck breeding success and harvest at larger spatial scales to support a comprehensive analysis of how well the harvest reflects reproductive output.

Waterbird counts on large water bodies: comparing ground and aerial methods during different ice conditions.

The aerial and ground methods of counting birds in a coastal area during different ice conditions were compared. Ice coverage of water was an important factor affecting the results of the two methods. When the water was ice-free, more birds were counted from the ground, whereas during ice conditions, higher numbers were obtained from the air. The first group of waterbirds with the smallest difference between the two methods (average 6%) contained seven species: Mute Swan Cygnus olor, Whooper Swan Cygnus cygnus, Greater Scaup Aythya marila, Tufted Duck Aythya fuligula, Common Goldeneye Bucephala clangula, Smew Mergellus albellus and Goosander Mergus merganser; these were treated as the core group. The second group with a moderate difference (average 20%) included another six species: Mallard Anas platyrhynchos, Eurasian Wigeon Mareca penelope, Common Pochard Aythya ferina, Great Crested Grebe Podiceps cristatus and Eurasian Coot Fulica atra. The third group with a large difference (average 85%) included five species, all of the Anatini tribe: Gadwall Mareca strepera, Northern Pintail Anas acuta, Northern Shoveler Spatula clypeata, Eurasian Teal Anas crecca and Garganey Spatula querquedula. During ice conditions, smaller numbers of most species were counted from the ground. The exception here was Mallard, more of which were counted from the ground, but the difference between two methods was relatively small in this species (7.5%). Under ice-free conditions, both methods can be used interchangeably for the most numerous birds occupying open water (core group) without any significant impact on the results. When water areas are frozen over, air counts are preferable as the results are more reliable. The cost analysis shows that a survey carried out by volunteer observers (reimbursement of travel expenses only) from the land is 58% cheaper, but if the observers are paid, then an aerial survey is 40% more economical.

Sustainable management of migratory European ducks: finding model species

Eurasian migratory duck species represent a natural resource shared between European countries. As is evident throughout human harvest history, lack of coordinated management and monitoring at appropriate levels often leads to ‘the tragedy of the commons’, where shared populations suffer overexploitation. Effective management can also be hampered by poor understanding of the factors that limit and regulate migratory populations throughout their flyways, and over time. Following decades of population increase, some European duck populations now show signs of levelling off or even decline, underlining the need for more active and effective management. In Europe, the existing mechanisms for delivering effective management of duck populations are limited, despite the need and enthusiasm for establishing adaptive management (AM) schemes for wildlife populations. Existing international legal agreements already oblige European countries to sustainably manage migratory waterbirds. Although the lack of coordinated demographic and hunting data remains a challenge to sustainable management planning, AM provides a robust decision‐making framework even in the presence of uncertainty regarding demographic and other information. In this paper we investigate the research and monitoring needs in Europe to successfully apply AM to ducks, and search for possible model species, focusing on freshwater species (in contrast to sea duck species) in the East Atlantic flyway. Based on current knowledge, we suggest that common tealAnas crecca,Eurasian wigeonMareca penelopeand common goldeneyeBucephala clangularepresent the best species for testing the application of an AM modelling approach to duck populations in Europe. Applying AM to huntable species with relatively good population data as models for broader implementation represents a cost effective way of starting to develop AM on a European flyway scale for ducks, and potentially other waterbirds in the future.

Do environmental conditions experienced in early life affect recruitment age and performance at first breeding in common goldeneye females?

Environmental conditions experienced early in life may have long‐term impacts on life history traits and reproductive performance. We investigated whether ambient temperature experienced during the first two to four weeks of life and weather severity during the first two winters affected recruitment age and relative timing of breeding in the year of recruitment in female common goldeneyes Bucephala clangula. Our sample consisted of 141 female recruits hatched in a study population in central Finland between 1985 and 2013 and captured later as breeders. About 56% of the recruited females bred for the first time when two years old (range 2–6 yr). Individuals facing colder ambient temperatures during the first two to four weeks posthatch or more severe winter conditions during the first two winters did not recruit at an older age. Nor did maternal characteristics, relative hatch date or nest site availability affect recruitment age. For females that recruited at two years old, the date of first breeding was usually late relative to the population mean that year (mean difference 6.9 d, range –7 to 21 d). Our results suggest developmental buffering enables female goldeneye ducklings to mitigate the impacts of adverse environmental conditions experienced during the first weeks of life, at least in terms of first breeding.

Identifying demographic and environmental drivers of recruitment and population growth in a cavity‐nesting sea duck population

Traits with the greatest proportional effects on fitness are typically conserved, and traits with larger temporal variation frequently play a dominant role in population dynamics. We examined recruitment patterns and population growth in common goldeneyes Bucephala clangula (hereafter goldeneye), using Pradel mark–recapture models from a long‐term nest box study (1997–2010). Our objectives were to estimate recruitment (f ) and population growth (λ) relative to recruitment origin group (in‐situ or unknown), investigate environmental and density dependent effects on these parameters, and evaluate potential immigration patterns. We detected group‐specific differences for f (in‐situ: 0.47 ± 0.13 SE, unknown: 0.31 ± 0.04), and the proportion of boxes occupied by goldeneyes the year prior to recruitment had a significant negative effect on recruitment for the in‐situ group (β = –1.04; 85% CI –1.29, –0.78), and a positive effect for the unknown group (β = 0.45; 85% CI 0.30, 0.61). The negative box occupancy effect in the year prior to recruitment, when in‐situ yearling goldeneyes prospect for potential nest sites, suggests that local nesting densities may limit recruitment of locally hatched females. We identified two competitive models for λ, which averaged 1.04 ± 0.03 and included interactions between recruitment origin group and a linear temporal trend, and the proportion of ducklings marked two years prior. By evaluating all levels of marking effort on λ, we determined that even if all hatched ducklings were marked in a given year, the resulting in‐situ λ was consistently lower than all observed population‐level λs during the study, indicating that individuals produced outside of study area nest boxes contributed to λ. Though female goldeneyes are considered highly philopatric, our results suggest that female natal and breeding dispersal may be more prevalent than previously thought, and the spatial scale at which these processes occur requires further investigation.

Life history patterns, individual heterogeneity, and density dependence in breeding common goldeneyes of the northern boreal forest

Life history patterns and their associated tradeoffs influence population dynamics, as they determine how individuals allocate resources among competing demographic traits. Here we examined life history strategies in common goldeneyes Bucephala clangula (hereafter goldeneye), a cavity‐nesting sea duck, in the northern boreal forest of interior Alaska, USA. We used multistate capture–mark–recapture models to estimate adult survival, breeding probability, first‐year survival, and recruitment probability using a long‐term nest box study (1997–2010). We detected annual variation in adult survival, which varied from 0.74 ± 0.12 (SE) to 0.93 ± 0.06. In contrast, breeding probability remained relatively high and invariant (0.84 ± 0.11) and was positively related to individual nest success the year prior. Nonbreeding individuals in one year were more likely to remain a nonbreeder, than attempt to breed the following year. First‐year survival decreased with smaller residual duckling mass and larger brood sizes. Probability of recruitment into the breeding population conditioned on survival was constant during the study (0.96 ± 0.06), and did not vary among ages 2–5 yr‐old. Overall, goldeneyes exhibited high, but somewhat variable, adult survival, and high breeding and recruitment probabilities, which is consistent with observed patterns in bet‐hedging species that breed annually in high quality breeding environments, but whose reproductive output is often influenced by stochastic events. Demographic estimates from this study are among the first for goldeneyes within Alaska. Life history patterns are known to vary geographically, therefore, we recommend further examination of life history patterns within the distribution of goldeneyes.

Avian diets in a saline ecosystem: Great Salt Lake, Utah, USA

Saline lakes provide a prey-rich, predator-free environment for birds to utilize during migration and stopover periods. The Great Salt Lake (GSL), Utah is the largest salt lake in North America and is utilized by millions of migratory birds. It also is host to multiple commercial endeavors. Proposed expansion of commercial use of the GSL would result in increased impounded area and water extraction for mineral production, which may increase the GSL's salinity and negatively impact invertebrate abundance. I review previous literature and synthesize diets of avian species utilizing the GSL to determine the importance of each invertebrate species, including brine shrimp (Artemia franciscana) and brine flies (Ephydra spp.), and clarify the anthropogenic impacts on food sources and avian populations. Species considered are eared grebes (Podiceps nigricollis), northern shovelers (Anas clypeata), green- winged teals (Anas crecca), common goldeneyes (Bucephala clangula), American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus), Wilson's phalaropes (Phalaropus tricolor), red-necked phalaropes (Phalaropus lobatus), and California gulls (Larus californicus). Brine shrimp and brine fly adults are consumed by all species considered. Alterations in prey abundance due to increased salinity may alter the ability of the GSL to support large avian populations.

Recent Data on the Danube Delta (Romania) Avifauna from the 2014 and 2015 Summer Seasons

Abstract A number of faunistically interesting observations related to the avifauna of the Danube Delta (Romania) are presented. In the spring of 2015, a mass mortality event with a minimum of 118 dead birds occurred in a major Dalmatian Pelican Pelecanus crispus colony in the Black Sea lagoons caused by the avian flu virus, strain H5N1. A possible hybrid between Little Egret Egretta garzetta and Western Reef Heron Egretta gularis was observed. The first nesting of Ruddy Shelduck Tadorna ferruginea in the Danube Delta was documented. Goldeneye Bucephala clangula and Smew Mergus albellus are re-colonising the areas they abandoned in the early 20th century. New data regarding the relocation of Pallas’s Gull Larus ichthyaetus colony in the Danube Delta as a result of hydromorphological changes in the bay, nesting and defence strategies against Caspian Gulls Larus cachinnans are described. Probable nesting of Citrine Wagtail Motacilla citreola in the Danube Delta was documented in 2014 for the first time.

Generalist predator, cyclic voles and cavity nests: testing the alternative prey hypothesis.

The alternative prey hypothesis (APH) states that when the density of the main prey declines, generalist predators switch to alternative prey and vice versa, meaning that predation pressure on the alternative prey should be negatively correlated with the density of the main prey. We tested the APH in a system comprising one generalist predator (pine marten, Martes martes), cyclic main prey (microtine voles, Microtus agrestis and Myodes glareolus) and alternative prey (cavity nests of common goldeneye, Bucephala clangula); pine marten is an important predator of both voles and common goldeneye nests. Specifically, we studied whether annual predation rate of real common goldeneye nests and experimental nests is negatively associated with fluctuation in the density of voles in four study areas in southern Finland in 2000-2011. Both vole density and nest predation rate varied considerably between years in all study areas. However, we did not find support for the hypothesis that vole dynamics indirectly affects predation rate of cavity nests in the way predicted by the APH. On the contrary, the probability of predation increased with vole spring abundance for both real and experimental nests. Furthermore, a crash in vole abundance from previous autumn to spring did not increase the probability of predation of real nests, although it increased that of experimental nests. We suggest that learned predation by pine marten individuals, coupled with efficient search image for cavities, overrides possible indirect positive effects of high vole density on the alternative prey in our study system.