Sari Holopainen

Habitat use in ducks breeding in boreal freshwater wetlands: a review

Breeding habitats strongly influence duck reproduction and survival. The boreal biome harbours a large share of the world’s wetlands, which are important breeding sites for several duck species. Based on 98 studies in the peer-reviewed literature, we here synthesize and evaluate which habitat characteristics affect habitat use and reproduction of ducks breeding in boreal freshwater wetlands with respect to (1) species and guild (dabbling, diving and piscivorous ducks) and (2) breeding cycle stage (settling by pairs, nesting and brood rearing). We consider the following aspects related to habitat: wetland morphology and spatial aggregation, water characteristics, habitat structure and vegetation, and biotic interactions. Most of the peer-reviewed studies of duck habitat use in boreal wetlands are from North America and Fennoscandia, while nearly half of the boreal area lacks such studies. Few species dominate research thus far while several others have not been studied at all. Nest site use and success are mainly related to predator avoidance. Food resources and habitat structure are the key characteristics affecting habitat use by duck pairs and broods as well as breeding success, although there are differences between duck guilds. Among the commonly studied variables, there is little evidence that water characteristics affect duck habitat use or survival. The most notable knowledge gaps are found in the effects of anthropogenic activities on habitat use and breeding success of ducks. Because boreal breeding environments are increasingly affected by human activities, we underline the need for future studies combining climate variation with natural and anthropogenic disturbances.

Mechanisms of density dependence in ducks: importance of space and per capita food

The growth rate of populations usually varies over time, often in a density-dependent manner. Despite the large amount of literature on density dependence, relatively little is known of the mechanisms underlying the density-dependent processes affecting populations, especially per capita natality. We performed a 20-year study on the density dependence of brood production in two duck species differing in the stability of habitat use. Our study was conducted in a boreal watershed in southern Finland. We predicted that a diving duck common goldeneye Bucephala clangula, with more stable habitat use, would show stronger density dependence than a dabbling duck common teal Anas crecca. We investigated reproductive output in relation to the duck pair density per se as well as in relation to per capita food availability. As predicted, the reproductive output of the goldeneye showed a more density-dependent pattern than that of the teal. The number of goldeneye broods per pair decreased when the pair density increased. This was not the case with the teal. However, when the breeding success was measured by taking into account per capita food availability, both species showed density dependence. Our results imply that the occurrence of density dependent processes may vary even in sympatric ducks breeding in the same, relatively stable landscape. Our analysis also emphasizes that it is important to take into account per capita resource availability when studying the density dependence of breeding success. Both findings have important implications for the management and conservation of species.

Habitat associations and habitat change: seeking explanation for population decline in breeding Eurasian wigeon Anas penelope

We explored whether the recent large-scale population decline of Eurasian wigeon (Anas penelope) in Europe may be linked to long-term vegetation changes in their boreal breeding wetlands. First, we assessed the importance of Equisetum, Phragmites, and Carex stands in lake selection by pairs and in foraging habitat selection by broods. Second, in 2013–2014 we revisited 58 lakes in Sweden and Finland studied in 1990–1991, to examine if there had been any long-term change in the abundance of habitat types preferred by wigeon. Finally, using continuous long-term data on breeding numbers of wigeon in 18 of the lakes studied in 1990–1991, we examined if wigeon numbers had changed at lakes where the habitat also had changed. We found that lake occupation of nesting wigeon pairs and foraging habitat use of broods were associated with the extent of Equisetum stands. The presence and abundance of this preferred habitat declined dramatically from 1990–1991 to 2013–2014 in the lakes from which the presence–absence data of wigeon emanate. Breeding numbers of wigeon showed a long-term declining trend in lakes where Equisetum has decreased. Our results imply that the recent population decline of wigeon in Europe may be linked to decrease of Equisetum habitat.

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 teal Anas crecca, Eurasian wigeon Mareca penelope and common goldeneye Bucephala clangula represent 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.

Recovering Whooper Swans do not cause a decline in Eurasian Wigeon via their grazing impact on habitat

AbstractThe Whooper Swan (Cygnus cygnus) is a good example of successful conservation, with rapidly growing numbers in Fennoscandia in recent decades. To the contrary, Eurasian Wigeon (Mareca penelope) shows a strong negative trend in breeding numbers, which raises conservation concerns. Previous research suggests a causal link between recent population trajectories of the two species. Both preferentially breed on wetlands with abundant horsetail (Equisetum spp.), a plant providing food for Whooper Swan and crucial feeding microhabitat for Eurasian Wigeon broods. We here test predictions based on the hypothesis that grazing on Equisetum by Whooper Swan reduces breeding habitat or breeding habitat quality for Eurasian Wigeon. We use data from 60 lakes in which waterfowl were counted in 1990–1991 and 2016, and Equisetum was mapped in 1990–1991 and 2013–2014. Lakes colonized by Whooper Swan typically had more abundant Equisetum vegetation in the past than lakes not colonized. Lake-specific decrease of Equisetum was not associated with colonization by Whooper Swan. The number of lakes occupied by Eurasian Wigeon decreased, but the decrease was not stronger on lakes colonized by Whooper Swan than on those that were not. Contrary to our prediction, current Eurasian Wigeon abundance was positively associated with Whooper Swan abundance. Moreover, Eurasian Wigeon did not decrease more on lakes from which Equisetum disappeared than on lakes in which there was still Equisetum left. This study does not support the idea that Whooper Swan affects Eurasian Wigeon negatively by grazing on Equisetum.ZusammenfassungWiedererstarken der Singschwäne-Populationen verursacht durch das Grasen im gleichen Habitat keinen Rückgang der Pfeifente Mit seinen in Fennoskandinavien in den letzten Jahrzehnten rasch gewachsenen Populationen stellt der Singschwan (Cygnus cygnus) ein gutes Beispiel für gelungenen Artenschutz dar. Im Gegensatz dazu zeigt die Pfeifente (Mareca penelope) in der Anzahl an Brutpaaren einen stark rückläufigen Trend, was zu Besorgnis im Naturschutz führt. Frühere Untersuchungen legen einen ursächlichen Zusammenhang zwischen den Populationsentwicklungen beider Arten nahe. Beide brüten bevorzugt in Feuchtgebieten mit starkem Schachtelhalmbewuchs (Equisetum spp.); diese Pflanze ist eine wichtige Nahrung für Singschwäne, während Pfeifenten bevorzugt in den Schachtelhalm-Habitaten brüten. Wir testeten Vorhersagen basierend auf der Hypothese, dass das Abweiden von Schachtelhalm durch Singschwäne das Brutareal der Pfeifenten verkleinert, bzw. dessen Qualität verringert. Wir verwendeten Daten von 60 Seen, auf denen die Anzahl an Wasservögeln 1990–1991 und auch 2016 gezählt und der Schachtelhalm-Bestand kartographiert wurde (1990–1991 und 2013–2014). Seen mit Singschwänen hatten typischerweise früher mehr Schachtelhalmvegetation als solche ohne Singschwäne. Ein für bestimmte Seen spezifischer Rückgang des Schachtelhalms stand in keinem Zusammenhang mit einer Besiedlung durch Singschwäne. Die Anzahl der von Pfeifenten besiedelten Seen ging zurück, aber dieser Rückgang war auf Seen mit Singschwänen nicht stärker als auf solchen ohne Singschwäne. Entgegen unserer Vorhersage korrelierte das Vorkommen von Pfeifenten sogar positiv mit dem von Singschwänen. Außerdem ging der Bestand an Pfeifenten auf Seen mit rückläufiger Schachtelhalmvegetation nicht stärker zurück als auf Seen mit gleichbleibendem Schachtelhalmbestand. Unsere Untersuchung konnte die Idee, dass Singschwäne durch ihr Abweiden von Schachtelhalm einen negativen Einfluss auf Pfeifenten hätten, nicht unterstützen.