Nest predation and climate change as drivers of alternative reproductive tactics in a migratory species

Alternative reproductive tactics enable individuals to choose a reproductive tactic relative to their status and prevailing environmental conditions in a way that increases their fitness. For example, females in many avian species show phenotypic plasticity and employ alternative reproductive tactics to cope with changes in predation risk and climate. Conspecific brood parasitism (CBP), in which females lay eggs in nests of conspecifics, is one example of such behaviour. It has been proposed that when prospects for successful nesting are low and/or costs of reproduction are high, females employ tactics of low effort such as non-breeding and parasitic laying. When environmental conditions are ideal and prospects for success high, females can increase their reproductive effort above typical nesting by laying parasitic eggs prior to initiating their own nest. Here, I used this flexible life-history strategy concept and long-term (1994‒2022) population level data of the common goldeneye Bucephala clangula to study how the rate of parasitic laying varies in relation to variation in nest predation risk and in the timing and length of the breeding season, the latter being measured by the timing of ice breakup. Nest predation rate in the previous year and timing of ice breakup interactively affected parasitic laying, the rate of parasitic laying being particularly high in years with late ice breakup and high nest predation rate in the previous year. Furthermore, the proportion of predated eggs was lower in parasitized nests than in non-parasitized nests, while the opposite was true for the proportion of eggs that failed in other way. As a consequence, the final number of young produced per nest was higher for parasitized nests. The findings of this study show that changes in environmental conditions affect the dynamics of alternative reproductive tactics in goldeneyes, with consequences to population level reproductive output

Impacts of climate‐driven changes in habitat phenology on dynamics of niche overlaps and spatial associations in a boreal waterbird community

A fundamental, yet little-explored, question is if climate change has affected niche relationships and spatial associations of native non-invasive species in established local communities, potentially affecting interspecific interactions and community organization. Here, long-term (1991‒2020) changes in habitat niche overlaps (HNOs; measured in terms of three habitat categories describing the amount and development of shore vegetation and shore depth) and spatial associations (SAs; measured as co-occurrence on lakes) were studied in relation to climate-driven changes in habitat phenology in a community of eight migratory waterbird species breeding on 37 lakes in southeastern Finland. Overall timing of ice-out date (IOD) and within-season variation in the timing of ice-out (standard deviation of IOD, SDIOD) in lakes determine habitat (lake) availability for waterbirds during the settling phase. Previous work has documented that IOD has advanced and SDIOD increased during 1991‒2020, with species responding differently to these changes in their habitat use. HNO and SA varied considerably in the 28 species pairs of eight species during the study period. The effect of IOD and SDIOD on that variation was generally small, effect sizes differing from zero only in eight out of 112 cases. However, the direction and magnitude of the effects of IOD and SDIOD on HNO and SA varied considerably among the species pairs. Although not statistically significant, overall differences in the direction and magnitude of the effect sizes suggested that the impacts of IOD and SDIOD on HNO and SA were stronger in species pairs in which the species were more similar in terms of settling phenology, and stronger for early settling species than for late settling species. Observed changes in niche relationships probably reflect changes in interspecific interactions and affect the possibilities for heterospecific information use in habitat selection

Nest and brood stage association between ducks and small colonial gulls in boreal wetlands

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European ducks in a changing world: human impacts, population processes and species interactions

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Extending temporal baseline increases understanding of biodiversity change in European boreal waterbird communities

Setting relevant temporal baselines is critical to understanding biodiversity change and the full impact of various pressures on biodiversity. Current knowledge of biodiversity change in European boreal waterbird communities is based on monitoring and other data from the last 35 years. However, the impact of the presumed main drivers of changes in these communities, i.e., eutrophication and alien predators, started decades before this. We used data of 35 breeding waterbird communities, representing both oligotrophic and eutrophic lakes, in southern Finland from 1951–1970 and 1996–2015 to study changes in biodiversity against a baseline from a period when the presumed main drivers were not yet fully effective. We found that species richness increased from 1951–1970 to 1996–2015 at oligotrophic lakes but not at eutrophic lakes; total abundance in turn increased at the former lake type but decreased at the latter. Breeding numbers of many historically abundant species declined at the eutrophic lakes to such a degree that the increases of other species were not sufficient to compensate for the declines. Population increases prevailed at the oligotrophic lakes and the slight declines of some previously less abundant species, were compensated for. The species level results revealed that local abundances of different species likely are affected by different drivers, suggesting that we need an autecological approach in the conservation management of boreal waterbird communities. Increased predation risk rather than eutrophication appeared to be the main biodiversity stressor in the waterbird communities studied

When good turns to bad and alien predators appear: The dynamics of biodiversity change in boreal waterbird communities

Temporal patterns of biodiversity are often difficult to interpret because of our limited understanding of how communities vary through time and how processes drive this variation. A further challenge with dynamic systems is choosing an appropriate baseline against which biodiversity change is judged. We used abundance time series of breeding waterbirds in eutrophic lakes in Finland for 1946–2022 to study the dynamics of biodiversity change in local communities and the relative role of two presumed main drivers, i.e. eutrophication and alien predators, in contributing to historical and recent trends in local abundances and biodiversity. We set the cut-off for the historical and recent study periods in the mid-1980 s, because the systematic monitoring of breeding waterbirds in Finland started in 1986 and recent analyses of biodiversity change and population trends in European boreal waterbird communities are mainly based on time series and data gathered since 1986. Both species richness and the total abundance of waterbirds in local communities showed contrasting trends between historical (gathered before the mid-1980 s) and current (gathered after the mid-1980 s) community time series, with the current time series indicating a decline and the historical time series indicating an increase. The abundances of habitat specialists (species preferring eutrophic lakes) and habitat generalists (species using both eutrophic and oligotrophic lakes) showed a corresponding difference between the current and historical time series. The local extinction rates were higher among habitat specialists than among habitat generalists. The trend indices for wetland-nesting species (highly vulnerable to predation by two alien species (the raccoon dog, Nyctereutes procyonoides, and American mink, Neovison vison) in terms of nest site) abundances were more negative than the trend indices of species nesting further away from waterbodies (less vulnerable to predation by two alien species). In addition, bottom-feeding species (presumably more sensitive to negative impacts of eutrophication) did not show more negative population trends than surface-feeding species (presumably less sensitive to negative impacts of eutrophication). Regardless of equal sensitivity to negative impacts of eutrophication, two species highly vulnerable to two alien predators showed more negative population trends than a less vulnerable species. The results suggest that increased predation has been an important driver of the population and biodiversity declines in the studied waterbird communities. The mid-1980 s may not provide an ecologically appropriate baseline against which changes in the populations and biodiversity of boreal waterbird communities are judged

Nuoret haapanasaaliissa – saalisosuuden muutokset ja säätekijöiden merkitys vuosien välisessä vaihtelussa

Summary: The proportion of juveniles in the hunting bag of Eurasian wigeon in Finland – long-term changes and the role of climatic conditions in explaining among-year variation The proportion of first-year birds in annual wing samples provided by hunters has been used as a measure of breeding success in waterfowl. The proportion of first-year birds in the wing samples of Eurasian wigeon Mareca penelope from Denmark and the United Kingdom shows a long-term decline, probably reflecting a decrease in breeding success. However, previous studies report conflicting results in the relationship between variation in the proportion of first-year birds and variation in climatic conditions. Here, we summarize main results of a study (Pöysä & Väänänen 2018) in which we used wing data of hunter-shot Eurasian wigeon from Finland to study whether the proportion of first-year birds shows a similar long-term decline and whether among-year variation in the proportion of young is associated with variation in climatic conditions. In addition, we discuss possibilities to improve sustainable hunting of ducks in Europe based on stable isotope analysis of wing samples from hunter-shot birds. We found a long-term decline in the proportion of first-year birds (Fig. 1). The proportion of young also varied considerably between years, but this variation was not associated with weather or the climatic variables considered for the breeding and wintering periods. This was the case particularly when controlling for common trend (year) in the response variable and explanatory variables (Table 1). More research is needed concerning factors that affect long-term changes and annual variation in the proportion of young in the hunting bag and on the suitability of this index to measure productivity in ducks.Peer reviewe