Aythya Ferina Research Articles

Patterns of reproductive effort and success in birds: path analyses of long‐term data from European ducks

Summary We tested ecological hypotheses about timing of breeding and reproductive effort in birds, by analysing > 15‐year data sets for individually marked females in three species of Latvian ducks (northern shoveler, tufted duck, common pochard). Duckling survival and recruitment declined with advancing hatch date in pochard and tufted duck, after controlling for effects of female age and other factors with path analysis, a novel finding which indicates that fitness advantages associated with early hatching extended beyond the prefledging period. Logistic regression analysis suggested further that individual duckling prefledging survival was moderate in the earliest phase of the breeding season, greatest in mid‐season and lowest later on. However, selection acting against early hatched ducklings was surpassed by strong directional selection favouring recruitment of the earliest hatching females. The absolute and relative numbers of female recruits produced by a breeding female declined sharply with advancing hatch date in all species. Unlike previous studies, an hypothesized intraspecific trade‐off between duckling mass and brood size was detected, being very robust in two of three species. Unexpectedly, female age effects on recruitment were manifested only indirectly by several pathways, the most important being the earlier hatching dates of older females. Size‐adjusted body mass (i.e. condition index) was positively related to reproductive success, and was 2–8‐fold more influential than female size (indexed by wing length). Overall, fecundity‐independent variables (e.g. hatching date, weather, indices of duckling production and habitat quality) generally had 2–10 times greater influence on recruitment rates than did fecundity‐dependent variables such as female size or condition, duckling mass and brood size, suggesting a critical role for external environmental factors vs. individual female‐specific traits in the recruitment process.

External features and molecular sexing of the anomalous Pintail, Anas acuta, found at Hyo-ko Waterfowl Park, Niigata Prefecture, Japan

Phenotypic variation of the plumage including albinism and melanism is widely known among birds. On the other hand, morpho-chromatic variation of the plumage caused by hybridization has also been found in nature. Such an example is occasionally found in the Anatidae (Kuroda 1939), and possible hybrids of the Pintail Anas acuta with other species, e.g., Mallard (A. platyrhynchos), Teal (A. crecca), Baikal Teal (A. formosa), Gadwall (A. strepera), Wigeon (A. penelope), Shoveler (A. clypeata) and Pochard (Aythya ferina), were documented previously (Kuroda 1939). In fact, a presumptive hybrid between the Pintail and Bikal Teal was observed also in Hyo-ko Waterfowl Park, located in a suburb of Niigata City, Niigata Pref., Japan (Chiba, unpubl. data). During the course of bird-banding study in this Park, we incidentally found 2 unusual male Pintails, which were morphologically different from any known hybrids. The present study, therefore, was conducted to clarify the characters of these anomalous Pintails on the basis of macroscopic examination and molecular sexing.

Hunting disturbance on a large shallow lake: the effectiveness of waterfowl refuges

Disturbance is most likely to have an impact during those periods of the annual cycle when food is scarce and birds have difficulty in meeting their energy requirements. The provision of disturbance‐free refuges has been shown to enhance the abundance and diversity of waterfowl wintering on such sites. Lough Neagh, a large shallow lake in Northern Ireland, hosts internationally important numbers of wintering waterfowl, the most numerous being Common Pochard Aythya ferina, Tufted Duck A. fuligula, Greater Scaup A. marila and Common Goldeneye Bucephala clangula. Hunting is the predominant winter recreational activity. A small number of refuges have been provided to limit the effects of shooting disturbance on the wintering populations. The use of one of these refuges (Doss Bay) was studied during the winter of 1997/8 and compared with a non‐refuge site (Brockish Bay) during the winter of 1998/9. Shooting intensity was greater at weekends than midweek, and significantly more birds used the refuge at weekends than midweek during the shooting season. In contrast, significantly fewer birds were observed in Brockish Bay at weekends. This trend ceased when the shooting season closed, suggesting that the effect was due to shooting disturbance. Furthermore, significantly fewer birds used Doss Bay after the shooting season had closed, whereas significantly more birds were observed at Brockish Bay. Shooting disturbance had the greatest impact on dabbling duck species and rails at both sites. Diving ducks moved away from shoreline disturbance to shallow areas where they could still feed. The value of shoreline refuges for waterfowl populations on lakes is discussed.

The effect of human disturbance and flock composition on the flight distances of waterfowl species

Flocking bird species tolerate an approaching human up to a certain distance. We measured this distance, i.e., flight distance, to an approaching small boat for 11 waterfowl species. The flight distances correlated positively with flock size and species diversity (Shannon index H′) in species that showed relatively short flight distances when they were in a single-species flock. However, we did not observe such a correlation for single-species flocks that showed relatively long flight distances. Only pochards (Aythya ferina), a species with large individual variation in flight distances, showed a positive correlation between flight distance and flock size in both single- and multispecies flocks. Flight distance seemed to be affected by usage of the water area: flight distances tended to be longer for waterfowl species that use a water area for foraging than for those that use it primarily for resting. Thus, the behavior of actively foraging species may be more affected by human disturbances than that of resting species.

Migration patterns and sex ratios of diving ducks wintering in Northern Ireland with specific reference to Lough Neagh

Several duck species exhibit differential migration, whereby females settle further south than males on the winter grounds after the autumn migration. This is most exaggerated in the diving ducks. In Northern Ireland generally, the migration patterns of Common Pochard Aythya ferina, Tufted Duck A. fuligula, Greater Scaup A. marila, and Common Goldeneye Bucephala clangula are similar to those observed in Great Britain. On Lough Neagh in particular, the sex ratios of wintering flocks of diving ducks were observed between the winters of 1996 and 1999. On average, 79% of Common Pochard, 72% of Tuf ted Duck and 66% of Common Goldeneye wintering on Lough Neagh were male. The possible reasons for differential migration of the sexes include body size dimorphism resulting in different cold temperature tolerances, advantages for males in returning to breeding grounds sooner and intersexual competition excluding the less competitive females to areas further south.

Effect of Conspecific Brood Parasitism on Host Fitness for Tufted Duck and Common Pochard

Abstract Brood parasitism occurs disproportionately in birds with precocial young and is particularly common in Anseriformes. In part, that pattern may result because precocial hosts, relative to altricial species, incur relatively few costs when caring for precocial eggs. Empirical data do not consistently support that hypothesis, and some parameters have not been adequately compared between parasitized and nonparasitized nests or females. We used a combination of experimentation (egg and duckling additions) and analysis of a larger observational data set to compare reproductive parameters, recruitment, and adult survival between parasitized and nonparasitized female Common Pochard (Aythya ferina) and Tufted Ducks (A. fuligula). Addition of three eggs to nests during the host's laying cycle had no effect on host clutch size, host egg hatch success, or nest success for either species. Nest success was not affected by parasitism intensity for pochards, but we did detect a small drop in nest success for Tufted Duck nests parasitized with >6 eggs. Recruitment probability did not differ between parasitized and nonparasitized nests for either species, and parasitism had no negative effect on adult survival. Between-year nest initiation dates were later for parasitized Tufted Ducks, although the biological consequences of that difference (3.8 days) seem negligible. Moderate levels of parasitism do not negatively affect hosts for these two species.

Effect of Conspecific Brood Parasitism on Host Fitness for Tufted Duck and Common Pochard

Effect of Conspecific Brood Parasitism on Host Fitness for Tufted Duck and Common Pochard

Duck nests and predators: interaction, specialisation and possible management

Low hatching success due to nest depredation has frequently been reported from waterfowl breeding sites, but current knowledge on relationships between duck nests and their predators, which should form a basis for successful management, remains incomplete. We used a 13‐year data set to test whether specific predator species are more successful in finding certain types of natural duck nests and whether there are interspecific differences in nest characteristics. Multinomial logistic regression allowed simultaneous evaluation of the effects of different factors, including their interactions. Significant predictors of duck nest fate were the presence of water edge and 3‐way interaction among presence of gull colonies, island type and clutch initiation date. Significant predictors of nest site use by duck species were: 3‐way interaction among presence of gull colonies, island type and clutch initiation date, 3‐way interaction among presence of gull colonies, island type and presence of water edge and 2‐way interaction between presence of water edge and clutch initiation date. The above interactions led to certain associations between duck species and predator species. Corvids (hooded crow Corvus corone cornix and raven Corvus corax) were responsible for depredating more mallard Anas platyrhynchos nests, but fewer common pochard Aythya ferina and tufted duck Aythya fuligula nests than expected. American mink Mustela vison was responsible for destroying more small Anas species (northern shoveler Anas clypeata, garganey Anas querquedula and gadwall Anas strepera) and tufted duck nests, but fewer mallard nests than expected. Marsh harrier Circus aeruginosus was apparently a generalist predator since we were not able to detect significant associations between this predator and nests of any specific duck species. We believe that examination of interactions between different factors affecting the probability that nests will be either successful or depredated by certain predator species may help waterfowl managers increase management success.

Does shooting disturbance affect diving ducks wintering on large shallow lakes? A case study on Lough Neagh, Northern Ireland

Waterfowl hunting is widespread and common throughout Europe, affecting waterfowl populations directly through the kill and indirectly through disturbance. Freedom from such disturbance is an important part of waterfowl management. However, most studies of the effects of disturbance on duck populations have been site specific with few attempts to synthesis the results of these local studies and use them in management strategies. Lough Neagh has the largest surface area of any freshwater lake in the British Isles. It is also relatively shallow with a mean depth of ca. 9 m. The seasonal effects of shooting disturbance on the daytime distributions and behaviour of wintering Pochard Aythya ferina, Tufted Duck A. fuligula, Scaup A. marila and Goldeneye Bucephala clangula was studied during the winter of 1998/1999. The nocturnal use of shoreline areas was also studied using an image-intensifing telescope. The distributions of wintering Pochard, Tufted duck and Scaup were shown to be affected by shooting disturbance on Lough Neagh. But because they were also shown to predominantly roost during the day, and were not observed to forage in the marginal areas of the Lough throughout the winter period at night, any energetic consequence of shoreline based shooting disturbance is likely to be small. Goldeneye predominantly fed during the day. It would be expected that diurnal feeding Goldeneye would show the biggest response to shooting disturbance during the day, but proportions observed in designated zones during and after the shooting season did not change significantly, confirming the lack of effect. Observation of Pochard and Tufted Duck engaged in various behaviours did show an increase in the proportion of ducks feeding, after the shooting season had closed. The increase was attributed to increased feeding prior to migration as opposed to being the result of the cessation of shooting disturbance. The most important factors to consider when applying conservation measures to diving duck populations wintering on lakes with similar attributes are identified and discussed.

EFFECT OF CONSPECIFIC BROOD PARASITISM ON HOST FITNESS FOR TUFTED DUCK AND COMMON POCHARD

Abstract Brood parasitism occurs disproportionately in birds with precocial young and is particularly common in Anseriformes. In part, that pattern may result because precocial hosts, relative to altricial species, incur relatively few costs when caring for precocial eggs. Empirical data do not consistently support that hypothesis, and some parameters have not been adequately compared between parasitized and nonparasitized nests or females. We used a combination of experimentation (egg and duckling additions) and analysis of a larger observational data set to compare reproductive parameters, recruitment, and adult survival between parasitized and nonparasitized female Common Pochard (Aythya ferina) and Tufted Ducks (A. fuligula). Addition of three eggs to nests during the host's laying cycle had no effect on host clutch size, host egg hatch success, or nest success for either species. Nest success was not affected by parasitism intensity for pochards, but we did detect a small drop in nest success for Tuf...

Recent Changes in Distribution of Wintering Populations of Waterfowl Established on the Basis of Lithuanian Ringing Recoveries

Recent changes in the wintering grounds of the Lithuanian breeding population of Mute Swan, Mallard, Common Pochard, and Coot were established by means of the analysis of the long-term ringing data stored in the Data Bank of the Lithuanian Bird Ringing Centre. Significant changes in the wintering grounds of Mute Swan and Mallard of the Lithuanian breeding population have occurred since the late 1980s; the wintering grounds of Common Pochard and Coot, on the other hand, have changed just unremarkably. These changes were primarily caused by human impact and an increased number of mild winters during the present climatic amelioration.

Possible Impacts of Climatic Conditions on Changes in Numbers and in Distribution of Certain Breeding and Staging Wildfowl Spsecies in Lithuania

The long-term changes in numbers and distribution of 13 wildfowl species breeding and staging in Lithuania were analysed. Three species of wildfowl (Tufted Duck Aythya fuligula, Common Pochard Aythya farina and Goosander Mergus merganser) became established in Lithuania as new breeding birds in the late 19th century and 3 other species (Whooper Swan Cygnus Cygnus, Common Shelduck Tadorna tadorna and Gadwall Anas strepera) did so during several past decades in the 20th century. Marked changes in numbers and distribution of migratory wildfowl populations were recorded during the last decades. It is likely that the recent changes in numbers and distribution of certain wildfowl species have been resulted in partly by climatic factors.

Diet selectivity and shift of wintering common pochards and tufted ducks in a eutrophic coastal lagoon

Diet selectivity and shift of common pochards ( Aythya ferina) and tufted ducks ( A. fuligula) were investigated in the eutrophic coastal lagoon, Lake Nakaumi, during three winters (1994–1997). These two diving ducks fed mainly on mussels Musculista senhousia, but used food resources differently. Common pochards foraged larger mussels that were depleted earlier than the smaller ones eaten by tufted ducks. After the mussel biomass decreased in late winter, tufted ducks shifted their diet to clams Ruditapes philippinarum and Crustacea, while common pochards shifted only to the clam. Thus, depletion of mussel biomass in the lagoon affected common pochards earlier and stronger than tufted ducks. We suggest that different use of food resources of each species influenced their wintering patterns. Tufted ducks used the wintering area for a long period, while common pochards moved to the other area when animal foods became less abundant.

Seasonal change in a filter-feeding bivalve Musculista senhousia population of a eutrophic estuarine lagoon

Filter-feeding bivalves often predominate the benthic biomass of estuaries, although their population size may drastically fluctuate due to physical and biological disturbances. To examine the recovery of a mussel population after periods of severe predation and anoxia, and to estimate the amount of nutrients removed from the system through mussel production, we surveyed, over 2 years, the Musculista senhousia population in the estuarine lagoon, Lake Nakaumi, Japan. Predation by diving ducks ( Aythya fuligula, Aythya ferina and Aythya marila) during winter dramatically reduced the mussel biomass in both years, but recruitment of juvenile mussels sustained the population. Anoxia during the second summer severely reduced the mussel population, resulting in less biomass than in the autumn of the previous year. Potential annual removal of nitrogen and phosphorus from the lagoon water through burial of M. senhousia shells under oxic conditions was estimated to be 7.1 and 5.1 tons, respectively. These are equivalent to 0.7% and 4.9% of the nitrogen and phosphorous annual load entering the lagoon via the main river. Under anoxic conditions, removal would decrease to only 5.6% of the potential amount.

Microhabitat characteristics of feeding sites used by diving duck Aythya wintering on the grossly polluted Manchester Ship Canal, UK

Nationally important wintering populations of up to 2700 Pochard Aythya ferina and 2000 Tufted Duck A. fuligula feed around Salford Docks in the upper reaches of the Manchester Ship Canal. The system is grossly organically polluted and devoid of aquatic macrophytes, but holds high densities of oligochaetes and other pollution-tolerant invertebrates. The species fed together and differences in feeding distributions were more apparent between day and night than they were between species or winter period. We related the spatial patterns of feeding by ducks to water depth, channel width, total organic benthic carbon levels, and invertebrate densities. Separate analyses were performed for each species, during nighttime and daytime, and for different periods of the winter. In only half these analyses could feeding patterns be explained by differences in the microhabitat variables. However, feeding by both species was concentrated in the wider portions of the docks, in areas with high densities of oligochaetes, but particularly in areas of high total benthic organic carbon. These were areas where large amounts of sewage matter are deposited in the benthos. There are plans to improve water quality in the docks by modernizing sewage treatment systems upstream and by oxygenating the water within the docks. These may generally improve the biology of the system , but they may have a serious impact on the numbers of diving ducks by reducing the densities of their invertebrate prey.

Impact of Disturbance on Waterfowl Wintering in a UK Dockland Redevelopment Area

One of the UK's largest flocks of pochard Aythya ferina and tufted duck A. fuligula winters in Manchester's busy dockland redevelopment area. I examined the effects of human disturbance on the population, and used this information to recommend minimal land-use restrictions that will help ensure the population's continued use of the site. Birds fed at the docks every night, but on 75% of days, the flock flew to suburban or rural refuges in response to disturbance. The common causes of disturbance, particularly pedestrians, did not affect the duck greatly, but disturbances associated with building and redevelopment of the site (e.g., machinery) often made duck evacuate the dock. While birds were no less likely to evacuate the docks as the winter progressed, they did show some short-term flexibility in their responses to disturbance. For example, birds appeared able to sit out disturbances throughout the afternoon if they had avoided evacuation of the docks during the morning. Birds spent only a small proportion of time feeding, and feeding activity was not heightened following periods of exclusion from the docks due to disturbance. Daytime feeding activity was elevated during periods of lowering temperatures, and despite heavy disturbance at the site, the impact of disturbance may only be significant during the coldest period of the winter. During very cold spells, it is important to limit the incidence of unusual disturbances, such as evening concerts and waterborne activities which tend to make duck evacuate the site.

Predation risk associated with nesting in gull colonies by two Aythya species: observations and an experimental test

To reduce nest predation certain duck species nest in association with more aggressive species. For instance, Pochard Aythya ferina and Tufted Duck Aythya fuligula often nest in association with small larids, such as the Black‐headed Gull Larus ridibundus. I studied nest predation, nesting association and nest site requirements of Pochard and Tufted Duck in central Finland (63°N, 27°E) observing natural and artifical nests. Predation of Pochard and Tufted Duck nests was of similar extent and stronger outside than within gull colonies. An experiment with artficial nests also showed that a higher proportion of nests was preyed upon outside than within gull colonies (0.98 and 0.13, respectively). The results are consistent with the hypothesis that nest predation is lower within than outside gull colonies. Tufted Ducks nest more often with gulls than do Pochards; 61.5% of Tufted Duck nests and 29.3% of Pochard nests were found within gull colonies.

Body-mass Dynamics of King Eiders During Incubation

Several studies have demonstrated the importance of maintaining parental body reserves to successfully complete incubation or to raise offspring without affecting parental survival (e.g. Tombre and Erikstad 1996, Merila and Wiggins 1997, Zicus 1997). Restraint in use of reserves could be favored if females with greater reserves after laying had higher reproductive success or survival. Erikstad and Tveraa (1995) suggested that optimal clutch size in Common Eiders (Somateria mollissima) is determined by an interaction between allocation of endogenous reserves to egg production and energy needed for incubation and brood rearing. Depletion of reserves before hatching may lead to nest failure through nest abandonment or decreased nest attentiveness. Moreover, high nest attentiveness may reduce predation by reducing the amount of time that nests are unattended and by reducing incubation duration (Milne 1976, Aldrich and Raveling 1983). Nest failure during incubation, therefore, may be a consequence of nest abandonment or predation, either of which may be linked to female body condition. Gloutney and Clark (1991) found that female Mallards (Anas platyrhynchos) and Northern Shovelers (A. clypeata) that nested successfully were heavier than unsuccessful females, but this pattern was absent in Blue-winged Teal (A. discors). Canvasbacks (Aythya valisineria) and Redheads (Aythya americana) used stored reserves during egg production and incubation, but body mass during late incubation predicted nesting success only for yearling Canvasbacks (Arnold et al. 1995). Blums et al. (1997) investigated this hypothesis in a large sample of Common Pochards (Aythyaferina) and Tufted Ducks (A. fuligula); late-incubation body mass predicted nesting success in Tufted Ducks and adult Common Pochards, but not in yearling Common Pochards. Hence, whereas all three studies documented effects of body mass on nesting success, in at least some species and/or age groups, these effects did not apply. Because arctic-nesting species contend with colder temperatures and possibly lower food availability

Mutual and Parasitic Mixed-feeding Associations in Waterfowl: A Food-addition Experiment.

To examine the effects of food availability on the organization of mixed-species feeding associations in Tundra Swans (Cygnus columbianus), Common Pochards (Aythya ferina) and Northern Pintails (Anas acuta), we observed their social and feeding behavior before and after the addition of artificial food (rice grains). The feeding associations occurred when the swans paddled their legs underwater to forage for sinking food. Pochards dived under paddling swans and Pintails foraged around the feeding associations of the two species. Before the addition of food, Tundra Swans showed the largest increase in dipping frequency in the three-species associations because more sinking food was stirred up by the feeding actions of Pochards. Pochards were also found to dive more frequently and for shorter periods in the three-species associations than solitary. Pintails in the mixed-species associations obtained more food by using three feeding techniques and by shortening the distance moved while dabbling. After the addition of rice grains, association size and aggressive interactions increased. Because frequent diving by many Pochards disturbed the feeding swans, the swans in the three-species associations had the lowest dipping frequency. However, Pochards and Pintails gathered around feeding swans despite the swans' aggressiveness and they still achieved greater feeding frequencies in the three-species associations than solitary. Therefore, the functional significance of mixed-feeding associations before the addition of food was based on mutualism but, after rice grains were provided, it was based on parasitism in which the hosts were Tundra Swans and the parasites were Pochards and Pintails. The most abundant participants in the three-species associations were Pochards and Tundra Swans were mainly aggressive toward them. Adding food led to an increase in the number of Pochards, which was costly for Tundra Swans. We concluded that the organization of mixed-species associations depended on the number of Pochards joining the feeding association.

Factors affecting changes in waterfowl populations in eutrophic wetlands in the Finnish lake district

From the 1970s to the 1990s, changes in breeding waterfowl populations were monitored at 26 well‐vegetated lakes in southern Finland. Extreme total population levels were found to differ by 40%, but between successive years fluctuations did not exceed 20%, the most unstable populations being garganey Anas querquedula, tufted duck Aythya fuligula, coot Fulica atra and pochard Aythya ferina. Multiple regression analysis was used to determine the effects of weather factors during wintering, spring and brood seasons on the variation in breeding waterfowl populations. The following weather factors were statistically significant in explaining fluctuations observed in four species; in garganey: spring temperature; in pintail Anas acuta: brood season temperature, winter severity in France and spring temperature; in goldeneye Bucephala clangula: winter severity in the Baltic and spring temperature; and in mallard Anas platyrhynchos: brood season temperature of the previous year. Mallard, teal Anas crecca, wigeon Anas penelope and goldeneye were shot in larger numbers than would be expected considering their respective proportions of the breeding waterfowl community. Hunting pressure on mallard, tufted duck and goldeneye was clearly higher in our study area than in other parts of Finland. Our results indicate that the level of hunting pressure in our study area may affect population densities of mallard.