Cool, cold or colder? Spatial segregation of prions and blue petrels is explained by differences in preferred sea surface temperatures

International audienceThe Southern Ocean provides one of the largest environmental gradients onEarth that lacks geographical barriers, and small but highly mobile petrelsliving theremay offer finemodels of evolution of diversity along environmentalgradients. Using geolocation devices,we investigated thewinter distribution ofclosely related petrel species breeding sympatrically in the southern IndianOcean, and applied ecological niche models to compare environmental conditionsin the habitat used. We show that thin-billed prions (Pachyptilabelcheri), Antarctic prions (Pachyptila desolata) and blue petrels (Halobaenacaerulea) from the Kerguelen archipelago in the southern Indian Ocean segregatelatitudinally, sea surface temperature being the most important variableseparating the distribution of the species. Antarctic prions spent the winternorth of the Polar Front in temperate waters, whereas blue petrels werefound south of the Polar Front in Antarcticwaters. Thin-billed prions preferredintermediate latitudes and temperatures. Stable isotope values of feathersreflected this near complete niche separation across an ecological gradientthat spans large scales, and suggest evolutionary isolation by environment.In pelagic seabirds that exploit large areas of ocean, spatial niche partitioningmay not only facilitate coexistence among ecologically similar species, butmay also have driven their evolution in the absence of geographical barriers.1. IntroductionIndividualmovements and behaviour are inextricably linked to habitat characteristics,which determine the distribution and availability of trophic resources.In the oceans, the more productive areas are often in cold-water or upwellingregions where higher nutrient availability sustains productive foodwebs. Seabirdspecies often breed in large communities and target productive areas within theirforaging range, leading to intense competition for resources [1] and reduced foragingefficiency [2]. Seabirds can avoid interspecific competition at least partiallyby ecological segregation in foraging areas [3,4], diving depths [4,5] or dietchoice [6,7]. However, little is known from pelagic birds during the non-breedingseason, when seabirds forage over much larger spatial scales. Among the mostabundant small seabirds worldwide, prions (Pachyptila spp.) and closely relatedblue petrels (Halobaena caerulea) inhabit the open waters of the Southern Ocean.As these small petrels are very similar in size, foraging techniques and dietduring the breeding season, it has been suggested that they may be suitablemodel species in the context of niche partitioning and community assemblyrules [8,9]. In the southwest Atlantic Ocean, thin-billed and Antarctic prionshad divergent patterns of migration, resulting in nearly complete spatial segregation(0–5% overlap by month, [10]). Consistent foraging in different water& 2015 The Author(s) Published by the Royal Society. All rights reserved