MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14714

ABSTRACT: Ecological niche theory predicts coexisting species are expected to segregate spatially, temporally or trophically to limit competition. Few studies have investigated niche segregation in multiple dimensions during the breeding season in sympatric morphologically similar seabird species. Moreover, these studies showed discrepancies between theoretical predictions and observational data. This study tests the hypothesis of niche segregation during breeding between two sympatric small-sized seabirds, the blue petrel Halobaena caerulea and the thin-billed prion Pachyptila belcheri by quantifying foraging niche and trophic differences. Combining at-sea movement GPS data and isotopic data (stable carbon and nitrogen), we assessed spatial, foraging habitat and trophic segregation. During incubation we found strong latitudinal and longitudinal segregation between species. Mean maximum distance from the colony during foraging trips was ≈2330 km and ≈1300 km for blue petrels and thin-billed prions, respectively. We found foraging habitat segregation during incubation, with blue petrels foraging close to the ice edge contrary to prions that foraged in oceanic areas far from ice. Although sample size was low, there was also some evidence for spatial and habitat segregation during chick-rearing, with prions foraging in areas with negative sea surface height anomalies. Trophic segregation was revealed by differences in stable isotopes with blue petrels feeding on higher-trophic level prey than did prions (mean δ¹⁵N in plasma 9.6 ± 0.4‰ and 9.0 ± 0.3‰ respectively). Spatial distribution and diet are the primary segregation mechanisms, and patterns of segregations may result from competitive exclusion rather than from niche specialization. Spatial and trophic segregation may have evolved to minimize competition allowing co-existence of these two abundant sympatric breeding species.