Nestling diet and parental food provisioning in a declining mountain passerine reveal high sensitivity to climate change

Mountain ecosystems naturally experience strong seasonal weather variations leading to a brief peak in food availability that constrains bird reproduction. Climate change accentuates both the intra- and interannual variability, which turn can reduce predictability of resources hence impact population demography. Yet, relatively little is known about influence environmental factors on breeding ecology mountain birds. Here, we quantified nestling diet provisioning behaviour Alpine ring ouzel Turdus torquatus alpestris, an emblematic declining thrush species typical central European treeline ecotones, relate these parameters local conditions. Nests were monitored with camcorders assess prey frequency identify items delivered by parents nestlings, as well estimate biomass. Our results indicate prominence earthworms (Lumbricidae) diet, terms abundance (80%) biomass (90%). Elevated ambient temperatures negatively impacted rates chicks parents, while rainfall had positive effect The mean item decreased throughout season, did proportion nestlings' diet. These findings highlight key role played parental behaviour, probably reflecting low staple source, earthworms, warm dry contexts. In particular, they underpin how climate alterations, notably increasing changing precipitation regimes, could Although effects reproductive performance dynamics still ought be studied, further our understanding ecological mechanisms potentially at play decline wildlife inhabiting high-elevation, climate-sensitive ecosystems.