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Phenotypic plasticity may enable individuals to cope with predictable and unpredictable environments during their life‐cycle. In that context, studying glucocorticoids—corticosterone (CORT) in birds—is relevant because of their primary role in allostasis. Higher baseline CORT levels are classically associated with environmental constraints and lower fitness (the CORT‐fitness hypothesis). However, in some environments, higher baseline CORT levels can promote reproduction, therefore being associated with higher fitness (the CORT‐adaptation hypothesis). These two hypotheses have been tested in multiple systems but rarely in a context of fluctuating predation threat.We used a long‐term individual‐based monitoring of baseline CORT levels in female common eiders Somateria mollissima (nCORT = 1537; nindividual = 790; 2009–2022) to disentangle the context‐dependent links between environmental conditions, CORT and fitness. Importantly, the study population has been facing a drastic increase in predation pressure over the past decades, linked to the recovery of the white‐tailed eagle Haliaeetus albicilla. Additionally, eiders breed on open or forested islands, further affecting adult and nest predation risk. This system allowed us to disentangle the relative contributions of within‐ and among‐individual variation in baseline CORT levels under predation.Supporting the CORT‐adaptation hypothesis, baseline CORT levels were positively associated with reproductive investment (clutch size), age and hatching success. By partitioning within‐ and among‐individual effects, we showed that at the individual level, CORT flexibly increased with clutch size and age. Females displaying higher CORT levels were more successful, suggesting a link between CORT and individual quality.At both the population and individual levels, baseline CORT levels decreased over the study period. This decrease was correlated with an increase in predation risk. Females had reduced baseline CORT when nesting under high eagle abundance or adult predation risk (within‐individual effect). Interestingly, apparent plasticity towards adult predation risk was only observed on open islands, likely reflecting habitat‐dependent strategies.Consistent with the CORT‐adaptation hypothesis, we show that changes in predation regime not only correlate with changes in reproductive investment, but also with rapid plastic adjustment of glucocorticoid levels and therefore individual strategies to cope with predation risk. Given the correlative nature of our study, we encourage further experimental studies testing for a causal relationship between predation and corticosterone levels. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Plastic and selective mechanisms govern parental investment adjustments to predation threat. We investigated the relative importance of plasticity and selection in risk-taking propensity of incubating female common eiders Somateria mollissima facing unprecedented predation in SW Finland, Baltic Sea. Using a 12-year individual-based dataset, we examined within- and among-individual variation in flight initiation distance (FID), in relation to predation risk, nest detectability, individual traits and reproductive investment (NFID = 1009; Nindividual = 559). We expected females nesting in riskier environments (higher predation risk, lower nest concealment) to mitigate environmentally imposed risk by exhibiting longer FIDs, and females investing more in current reproduction (older, in better condition or laying larger clutches) to display shorter FIDs. The target of predation—adult or offspring—affected the mechanisms adapting risk-taking propensity; females plastically increased their FID under higher adult predation risk, while risk-avoiding breeders were predominant on islands with higher nest predation risk. Risk-taking females selected thicker nest cover, consistent with personality-matching habitat choice. Females plastically attenuated their anti-predator response (shorter FIDs) with advancing age, and females in better body condition were more risk-taking, a result explained by selection processes. Future research should consider predator type when investigating the fitness consequences of risk-taking strategies. [ABSTRACT FROM AUTHOR]

Anthropogenically introduced invasive species represent a major threat to global biodiversity by causing population declines and extinctions of native species. The negative impacts of introduced predators are well documented, yet a fundamental knowledge gap exists regarding the efficiency of potential mitigation methods to restore the ecosystem. Other understudied aspects concern prey behavioural antipredator responses and the historical context of native predator–prey interactions, which may moderate invasion impacts on native prey. Invasion impacts of American mink (Neovison vison) and raccoon dog (Nyctereutes procyonoides) into the Baltic Sea archipelago are poorly understood, and the efficiency of removal efforts as a means to alleviate depredation pressure on native prey is debated. Here, we examine the effectiveness of invasive predator removal on ground-nesting female common eider (Somateria mollissima) mortality, breeding success and breeding propensity over a 9-year period, while controlling for predation risk imposed by the main native predator, the white-tailed eagle (Haliaeetus albicilla). Our results clearly show that intensified removal of American minks and raccoon dogs decreased the number of female eiders killed during nesting, while improving both nesting success and breeding propensity. Such obvious positive effects of invasive predator removal are particularly noteworthy against the backdrop of a soaring eagle population, indicating that the impacts of invasives may become accentuated when native predators differ taxonomically and by hunting mode. This study shows that invasive alien predator removal is an effective conservation measure clearly aiding native fauna even under severe native predation pressure. Such cost-effective conservation actions call for governmental deployment across large areas. [ABSTRACT FROM AUTHOR]

Increasing urbanisation and human pressure on lands have huge impacts on biodiversity. Some species, known as "urban exploiters", manage to expand in urban landscapes, relying on human resources. The House Sparrow (Passer domesticus) is the perfect example of a human-commensal species. Surprisingly, this urban exploiter has been declining all over Europe over the past decades. The proximate causes of this decline remain poorly understood. We particularly lack understanding about urban habitat characteristics that are particularly unfavourable for House Sparrows. In the present study, we analysed fine-scale habitat characteristics of House Sparrow population sizes and trends using a fifteen-year House Sparrow census (2003–2017) covering the urban diversity of Paris (nearly 200 census sites), one of the densest European cities. We documented for the first time the dramatic decline (−89%) of the species in Paris over the study period. The temporal decline over the whole city correlates with the concomitant increase in the number of breeding Sparrowhawks. We could not detect statistical influences of annual variations in weather conditions and pollution. The decline of House Sparrows is spatially heterogeneous. Indeed, site-scale analyses revealed sharpest declines at sites that initially hosted the largest numbers of sparrows, which are areas with a relatively high proportion of green spaces and new buildings. Further experimental studies are now needed to disentangle the exact impact of specific characteristics of the urban environment on House Sparrow populations. [ABSTRACT FROM AUTHOR]

Background: Land-use change is one of the main drivers of the global erosion of biodiversity. In that context, it is crucial to understand how landscape characteristics drive the presence of rare endangered species. Nevertheless, it is also important to study common species in multiple habitats, because they represent a large proportion of biodiversity and are essential to maintain ecological functions. Interestingly, some habitats, as farmlands with permanent crops (e.g. vineyards), have been overlooked in the literature. Methods: In this study, we investigated the distribution of a widespread and common bird species, the Common Blackbird (Turdus merula), within and between the three main habitats of our study area (rural Western France). We specifically focused on (1) woodlands, (2) farmlands with a high vineyard coverage, and (3) moderately urbanized areas. Specifically, we aimed to assess the beneficial and detrimental effects of these habitats and their fine-scale composition on the presence of a common bird species, relying on a survey by point counts (nearly 100 locations). We studied the effects of habitats and gradients of fine-scale habitat composition on blackbird presence using logistic regression analyses. Results: Blackbirds were present in all studied habitats. However, their presence varied between habitats, being lower in vineyards than in woodlands and cities. In woodlands and cities, fine-scale analyses did not reveal any component driving the species’ presence. However, we found that shrub and tree vegetation cover had a significant positive effect on blackbird presence in vineyards. Conclusions: Our results are in agreement with the definition of a generalist species. Interestingly, species distribution varied between habitats. The high presence of blackbirds in urban areas suggests that medium-sized cities, despite their artificialization, do not constrain the settlement of this former forest specialist and that green spaces may allow blackbirds to thrive in medium-sized cities. On the contrary, we found an impoverished presence of blackbirds in vineyards and a positive effect of vegetation on their presence in these landscapes. This suggests that permanent crops, and more generally farmlands, may impose important constraints to common species. Future studies should examine how to enhance biodiversity through agricultural management policies, especially in vineyards. [ABSTRACT FROM AUTHOR]