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Habitat partitioning and molting site fidelity in Tetrao urogallus cantabricus revealed through stable isotopes analysis

Blanco-Fontao, Beatriz, Obeso, José Ramón, Bañuelos, María-José, Quevedo, Mario
Journal of ornithology 2012 v.153 no.2 pp. 555-562
Tetrao urogallus, deciduous forests, diet, feathers, females, grouse, males, microhabitats, molting, philopatry, rare species, sexual dimorphism, stable isotopes, treeline, trees, variance
Sexual dimorphism is often associated with different feeding strategies between sexes because of distinct nutritional demands or intake rates. Capercaillie (Tetrao urogallus) is the most sexually dimorphic grouse, thus sexual segregation in resource use is likely. This study assessed intrapopulation variation in the diet related to habitat use, focusing on differential feeding behaviors between Capercaillie females and males. We used stable isotopes analyses in feathers of Cantabrian Capercaillie, a population living at the southern edge of the range in purely deciduous forests. We analyzed feathers of females and males, and sorted them according to the dominant tree species in the patch where they were found. Mean isotopic values differed both between sexes and among forest types. The latter explained most of the isotopic variance, suggesting that birds consistently selected certain forest types to molt. Capercaillie females showed wider trophic niche and seemingly more intra-gender diversity in resource use than males. The differences between sexes in the trophic variability support the sexual segregation reported in previous studies which is associated with females using the more micro-habitat diverse treeline areas, while males mainly use the inner areas of the forests. Stable isotope analysis proved very useful to assess intersexual niche partitioning in rare species living in rugged terrains where it is logistically difficult to rely on direct approaches (i.e. direct observation, capture and radio-tracking).