Multi-scale effects of nestling diet on breeding performance in a terrestrial top predator inferred from stable isotope analysis

This is the final version of the article. Available from the publisher via the DOI in this record.Inter-individual diet variation within populations is likely to have important ecological and evolutionary implications. The diet-fitness relationships at the individual level and the emerging population processes are, however, poorly understood for most avian predators inhabiting complex terrestrial ecosystems. In this study, we use an isotopic approach to assess the trophic ecology of nestlings in a long-lived raptor, the Bonelli's eagle Aquila fasciata, and investigate whether nestling dietary breath and main prey consumption can affect the species' reproductive performance at two spatial scales: territories within populations and populations over a large geographic area. At the territory level, those breeding pairs whose nestlings consumed similar diets to the overall population (i.e. moderate consumption of preferred prey, but complemented by alternative prey categories) or those disproportionally consuming preferred prey were more likely to fledge two chicks. An increase in the diet diversity, however, related negatively with productivity. The age and replacements of breeding pair members had also an influence on productivity, with more fledglings associated to adult pairs with few replacements, as expected in long-lived species. At the population level, mean productivity was higher in those population-years with lower dietary breadth and higher diet similarity among territories, which was related to an overall higher consumption of preferred prey. Thus, we revealed a correspondence in diet-fitness relationships at two spatial scales: territories and populations. We suggest that stable isotope analyses may be a powerful tool to monitor the diet of terrestrial avian predators on large spatio-temporal scales, which could serve to detect potential changes in the availability of those prey on which predators depend for breeding. We encourage ecologists and evolutionary and conservation biologists concerned with the multi-scale fitness consequences of inter-individual variation in resource use to employ similar stable isotope-based approaches, which can be successfully applied to complex ecosystems such as the Mediterranean.Funding for this work was provided by projects CGL2007-64805 and CGL2010-17056 from the ‘‘Ministerio de Ciencia e Innovacio´n, Gobierno de Espan˜ a’’, the ‘‘A`rea d’Espais Naturals de la Diputacio´ de Barcelona’’, and Miquel Torres S.A. Fieldwork in France was carried out within the framework of the second National Action Plan for Bonelli’s eagle from the ‘‘Ministe`re franc¸ais de l’E´cologie, de L’E´nergie, du De´veloppement Durable et de la Mer’’ and coordinated by the DREAL LR ‘‘Direction Re´gionale de l’Environnement, de l’Ame´nagement et du Logement-Languedoc-Roussillon’’. J. Resano-Mayor was supported by a predoctoral grant from the ‘‘Departamento de Educacio´n, Gobierno de Navarra; Plan de Formacio´n y de I+D 2008–2009’’, and M. Moleo´n by a postdoctoral grant from the ‘‘Ministerio de Educacio´n, Gobierno de Espan˜ a; Plan Nacional de I+D+i 2008–2011’’. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Past and future impact of climate change on foraging habitat suitability in a high-alpine bird species : management options to buffer against global warming effects

The majority of predictions about the impacts of climate change on wildlife have relied either on the study of species' physiological tolerance or on broad-scale distribution models. In comparison, little attention has been paid to species' mechanistic responses to fine-grained, climate-induced modifications of habitat suitability. However, such studies would be pivotal to the understanding of species' ecological requirements (and hence their adaptive potential to environmental change) and the design of management strategies. We investigated foraging microhabitat selection in a potentially climate-change sensitive species, the white-winged snowfinch Montifringilla nivalis, during the breeding season in the Alps. Our microhabitat selection model considered topography, ground-cover variables and sward height within a 5-m radius at foraging and control locations. Habitat selection was positively affected by grassland cover, negatively by sward height and quadratically by snow cover (optimum around 40%); birds avoided anthropized (urban areas, roads) sites. We estimated past (1976) and future (2066) climate-driven changes in foraging microhabitat suitability, assuming a progressively earlier date of snowmelt due to increasing temperatures over this entire time span. We then modelled the potential impact of snowmelt (and related sward height) on habitat suitability under two scenarios: maintaining the current situation (i.e. irregular seasonal grazing) and implementing targeted management in an attempt to mitigate impacts of earlier snowmelt. Predicted foraging habitat suitability (estimated as the fraction of suitable plots) significantly declined over time ( 1223% between 1976 and 2016, further 32% loss by 2066). However, model outputs demonstrated that maintaining sward height below 6 cm on breeding grounds (e.g. by regular grazing) would significantly decrease the predicted loss of suitable foraging habitat. Detailed information about patterns of resource exploitation allows the identification of mechanistic, functional responses of species to environmental change, and enables an evaluation of habitat management options that can buffer against the detrimental effects of global warming