Resumen del producto

Ecologically similar species partition their use of resources and habitats and thus coexist due to ecological segregation in space, time, or diet. In seabirds, this segregation may dif- fer over the annual cycle or vary inter-annually. We evaluated niche segregation in 3 sympatric storm-petrel species (Hydrobates melania, H. leucorhous, and H. microsoma) from the San Benito Islands, Mexico, during 2012 and 2013. We used diet samples and carbon (d13C) and nitrogen (d15N) isotopic values obtained from egg membranes, blood, feathers, and prey. We used krill sam- ples to delineate marine d13C and d15N isoscapes for the Baja California Peninsula. During the breeding season, storm-petrels segregated regarding diet composition, stable isotope values, and isotopic niches. H. melania consumed higher trophic-position prey from neritic waters, while H. leucorhous and H. microsoma foraged on lower-trophic position prey from oceanic waters. Iso- topic niches among species did not overlap in 2013, whereas those of H. microsoma and H. leuco- rhous overlapped in 2012. The feeding strategies of H. melania varied among breeding phases, and adults consumed different prey items from different areas compared to those of their off- spring. H. microsoma adults and their chicks consumed the same prey items but from different habitats. During the non-breeding period, niche segregation between species persisted, except for H. microsoma and H. leucorhous during the molt of primary (P1) and undertail cover feathers. These 3 sympatric species coexist through niche segregation based on prey items and foraging areas that vary seasonally and year-round, probably due to changes in oceanographic conditions and the distribution and availability of prey.

Palabras clave: Ecological segregation; Seabird; diet; stable isotopes; Breeding phase; Marine isoscape; Oceanodroma

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