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Marine Ecology Progress Series

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MEPS 585:199-212 (2017)  -  DOI:

Seasonal shifts in foraging distribution due to individual flexibility in a tropical pelagic forager, the Ascension frigatebird

Steffen Oppel1,*, Sam Weber2,3, Nicola Weber2,3, Derren Fox2, Eliza Leat2, Jolene Sim2, Julia Sommerfeld1,4, Mark Bolton1, Annette C. Broderick3, Brendan J. Godley3

1RSPB Centre for Conservation Science, Royal Society for the Protection of Birds, The David Attenborough Building, Pembroke Street, Cambridge CB2 3QZ, UK
2Ascension Island Government Conservation Department, Georgetown, Ascension Island ASCN 1ZZ, South Atlantic
3Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn TR10 9FE, UK
4Institut für Tierökologie und Spezielle Zoologie, Justus Liebig Universität Gießen, Heinrich-Buff-Ring 38, 35392 Gießen, Germany
*Corresponding author:

ABSTRACT: Predators exploiting tropical pelagic waters characterised by low fluctuations in seasonal temperature and salinity may require different foraging strategies than predators that can rely on persistently productive marine features. Consistent individual differences in foraging strategies have been found in temperate seabirds, but it is unclear whether such foraging specialisation would be beneficial in unpredictable tropical pelagic waters. We examined whether foraging trip characteristics of a tropical seabird were consistent between seasons and within individuals and explored whether seasonal changes could be explained by environmental variables. Ascension frigatebird Fregata aquila trips lasted up to 18 d and covered a total travel distance of up to 7047 km, but adult frigatebirds stayed within a radius of 1150 km of Ascension Island. We found that the 50% utilisation distribution of the population expanded southwestward in the cool season due to individuals performing more and longer trips in a southerly and westerly direction during the cool compared to the hot season. Individual repeatability was low (R < 0.25) for all trip characteristics, and we were unable to explain seasonal changes in time spent at sea using oceanographic or atmospheric variables. Instead, frigatebird usage per area was almost exclusively determined by distance from the colony, and although individuals spent more time in distant portions of their foraging trips, the amount of time spent per unit area decreased exponentially with increasing distance from the colony. This study indicates that, in a relatively featureless environment, high individual consistency may not be a beneficial trait for pelagic predators.

KEY WORDS: Seabird · Satellite tracking · Individual consistency · Home range · Central-place foraging

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Cite this article as: Oppel S, Weber S, Weber N, Fox D and others (2017) Seasonal shifts in foraging distribution due to individual flexibility in a tropical pelagic forager, the Ascension frigatebird. Mar Ecol Prog Ser 585:199-212.

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