Conservation implications of consistent foraging and trophic ecology in a rare petrel species

Individuals within populations can use different resources, leading to ecological segregation and niche variation. This segregation could have direct impacts on the migratory strategy or breeding success, thus affecting the overall population and community dynamics and, ultimately, survival. In this study, we assessed the inter-annual and within individual foraging ecology of an endemic and highly threatened seabird species, the Desertas petrel Pterodroma deserta, during the breeding and non-breeding phases. We combined 54 annual tracks (26 individuals; 2009–2013) obtained with light-level loggers (Global Location Sensing or GLS loggers) with stable isotope analyses (δ15N and δ13C) of blood (plasma and cells) and feathers. Wide-ranging tracking data show that this species is a generalist predator, able to adapt to very different habitats. All birds remained faithful to their selected non-breeding areas over the years leading to very high spatial, temporal and trophic consistency among years (i.e. usually with intra-correlation coefficient values, which is an index of repeatability of > 40%). During both the breeding and non-breeding seasons, individual birds showed narrow and segregated isotopic niches, indicating a high level of specialization and limited choice of prey and habitats. The conservation of a seabird with such a dispersive (species-level) yet consistent (individual-level) non-breeding distribution pattern represents a challenge in marine policy terms. On the one hand, such a consistent temporal and spatial pattern will help with defining core areas for conservation, which could be protected through specific management measures or by the establishment of marine protected areas. Yet, their relatively large size (on average 4000 km2) and extent over both national and international waters, where different legislative frameworks apply, will require the coordinated action by many nations, international organizations and multilateral environmental agreements.

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