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The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) lives at one of the southernmost limits of the ptarmigan range. Their small population sizes and the impacts of global changes are limiting factors in the conservation of this threatened subspecies. An effective conservation policy requires precise basic knowledge of a species' food and habitat requirements, information that is practically non-existent for this Pyrenean population. Here, we describe the diet of a ptarmigan population in the Eastern Pyrenees, the environmental factors influencing its variability and the relationship between diet floristic composition and quality. Diet composition was determined by microhistological analysis of faeces and diet quality was estimated from free-urate faecal N content. Our results show that grouse diet is based mainly on arctic-alpine shrubs of the Ericaceae family, as well as dwarf willows (Salix spp.) and Dryas octopetala. The most frequently consumed plant species was Rhododendron ferrugineum, but its abundance in the diet was negatively related to the diet nitrogen content. Conversely, the abundance of Salix spp., grass leaves and arthropods increased the nitrogen content of the diet. Seasonality associated with snow-melting contributed the most to variability in the Pyrenean ptarmigan diet, differentiating winter from spring/summer diets. The latter was characterised by a high consumption of dwarf willows, flowers, arthropods and tender forb leaves. Geographic area and sex-age class influenced diet variability to a lesser extent. Current temperature increases in the Pyrenees due to global warming may reduce the persistence and surface area of snow-packs where preferred plants for rock ptarmigan usually grow, thus reducing food availability. The high consumption of Rh. ferrugineum characterised the diet of the Pyrenean population. Given the toxicity of this plant for most herbivores, its potential negative effect on Pyrenean ptarmigan populations should be evaluated. [ABSTRACT FROM AUTHOR]

The Pyrenean rock ptarmigan (Lagopus muta pyrenaica) is the southernmost subspecies of the species in Europe and is considered threatened as a consequence of changes in landscape, human pressure, climate change, and low genetic diversity. Previous studies have shown a relationship between the date of snowmelt and reproductive success in the Pyrenean ptarmigan. It is well established that birds laying early in the breeding season have higher reproductive success, but the specific mechanism for this relationship is debated. We present an explicative model of the relationship between snowmelt date and breeding success mediated by food quality for grouse in alpine environments. From microhistological analyses of 121 faecal samples collected during three years in the Canigou Massif (Eastern Pyrenees), and the assessment of the chemical composition of the main dietary components, we estimated the potential quality of individual diets. Potential dietary quality was correlated with free-urate faecal N, a proxy of the digestible protein content ingested by ptarmigan, and both were correlated with phenological stage of consumed plants, which in turn depends on snowmelt date. Our findings suggest that the average snowmelt date is subject to a strong interannual variability influencing laying date. In years of early snowmelt, hens benefit from a longer period of high quality food resources potentially leading to a higher breeding success. On the contrary, in years of late snowmelt, hens begin their breeding period in poorer nutrient condition because the peaks of protein content of their main food items are delayed with respect to laying date, hence reducing breeding performance. We discuss the possible mismatch between breeding and snowmelt timing. [ABSTRACT FROM AUTHOR]