TY - JOUR
T1 - Land or sea? Foraging area choice during breeding by an omnivorous gull
AU - Isaksson, Natalie
AU - Evans, Thomas J.
AU - Shamoun-Baranes, Judy
AU - Åkesson, Susanne
N1 - Funding Information:
The study was financed by grants to SÅ from the Swedish Research Council (621-2007-5930; 621-2010-5584, 621-2013-4361) with support from the Centre for Animal Movement Research (CAnMove) funded by a Linnaeus grant from the Swedish Research Council (349-2007-8690) and Lund University. The work was approved by the ethical committee for research with wild animals (Malmö/Lunds Djurförsöksetiska nämnd; permission number: M113-09), and for work within a protected area by the County Administrative Board (Länsstyrelsen, Gotland). NCEP Reanalysis 2 data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/. We thank the Baltic Seabird Project and Karlsö Jagt-och Djurskyddsförening AB for their cooperation and aid with field work at Stora Karlsö. We thank Arne Andersson, Johan Bäckman (both CAnMove, Lund University), Edwin Baaij, Willem Bouten (UVA-BiTS, Amsterdam University), Juliana Dänhardt, Tina D'Hertefeldt, Ola Olsson, and Martin Stjernman (Department of Biology, Lund University) for support and advice. We thank two anonymous reviewers for thoughtful and insightful comments and suggestions.
Funding Information:
The study was financed by grants to SÅ from the Swedish Research Council (621-2007-5930; 621-2010-5584, 621-2013-4361) with support from the Centre for Animal Movement Research (CAnMove) funded by a Linnaeus grant from the Swedish Research Council (349-2007-8690) and Lund University. The work was approved by the ethical committee for research with wild animals (Malmö/Lunds Djurförsöksetiska nämnd; permission number: M113-09), and for work within a protected area by the County Administrative Board (Länsstyrelsen, Gotland). NCEP Reanalysis 2 data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/. We thank the Baltic Seabird Project and Karlsö Jagt-och Djurskyddsförening AB for their cooperation and aid with field work at Stora Karlsö. We thank Arne Andersson, Johan Bäckman (both CAnMove, Lund University), Edwin Baaij, Willem Bouten (UVA-BiTS, Amsterdam University), Juliana Dänhardt, Tina D’Hertefeldt, Ola Olsson, and Martin Stjernman (Department of Biology, Lund University) for support and advice. We thank two anonymous reviewers for thoughtful and insightful comments and suggestions.
Publisher Copyright:
© 2016 Isaksson et al.
PY - 2016/5/15
Y1 - 2016/5/15
N2 - Background: Generalist predators may vary their diet and use of habitat according to both internal state (e.g. breeding stage) and external (e.g. weather) factors. Lesser black-backed gulls Larus fuscus (Linnaeus 1758) are dietary generalists, foraging in both terrestrial and marine habitats during breeding. We investigate what affects the gulls' propensity to forage at sea or on land. We assess the importance of terrestrial foraging to gulls in the Baltic Sea (sub. sp. L. f. fuscus), looking especially at their use of agricultural fields. Results: Through the GPS tracking of 19 individuals across 3 years we tracked 1038 foraging trips and found that 21.2 % of foraging trips were predominantly terrestrial, 9.0 % were a mix of terrestrial and marine, and 68.5 % were exclusively marine. Terrestrial trips were (1) more frequent when departing around sunrise, whereas marine trips occurred throughout the day. Additionally, trips with mostly land-based foraging decreased as the breeding season progressed, suggesting dietary switching coincident with the onset of chick provisioning. (2) During cloudy and cold conditions terrestrial foraging trips were more likely. (3) We found no differences between sexes in their land-based foraging strategy. (4) Gull individuals showed great variation in foraging strategy. Using observations of agricultural fields, carried out for one year, we found that (5) gulls preferentially foraged on fields with short vegetation, and there was a positive association with occurrence of waders and other species of gulls. (6) The availability and use of these preferred fields decreased through the breeding period. Conclusions: This study found high prevalence of terrestrial foraging during early breeding as well as support for dietary switching early in the breeding season. The overall tendency for marine or terrestrial foraging was consistent within individuals, with gull identity accounting for much of the variation observed in foraging trips. Our results suggest that anthropogenic terrestrial food sources may play a role in the low breeding success of these gulls through either variation in quantity and/or quality. Finally, our study demonstrates the potential of combining data from GPS-tracking of individual animals with the 'ground-truthing' of habitat visited to elucidate the otherwise nebulous behavior of a generalist predator.
AB - Background: Generalist predators may vary their diet and use of habitat according to both internal state (e.g. breeding stage) and external (e.g. weather) factors. Lesser black-backed gulls Larus fuscus (Linnaeus 1758) are dietary generalists, foraging in both terrestrial and marine habitats during breeding. We investigate what affects the gulls' propensity to forage at sea or on land. We assess the importance of terrestrial foraging to gulls in the Baltic Sea (sub. sp. L. f. fuscus), looking especially at their use of agricultural fields. Results: Through the GPS tracking of 19 individuals across 3 years we tracked 1038 foraging trips and found that 21.2 % of foraging trips were predominantly terrestrial, 9.0 % were a mix of terrestrial and marine, and 68.5 % were exclusively marine. Terrestrial trips were (1) more frequent when departing around sunrise, whereas marine trips occurred throughout the day. Additionally, trips with mostly land-based foraging decreased as the breeding season progressed, suggesting dietary switching coincident with the onset of chick provisioning. (2) During cloudy and cold conditions terrestrial foraging trips were more likely. (3) We found no differences between sexes in their land-based foraging strategy. (4) Gull individuals showed great variation in foraging strategy. Using observations of agricultural fields, carried out for one year, we found that (5) gulls preferentially foraged on fields with short vegetation, and there was a positive association with occurrence of waders and other species of gulls. (6) The availability and use of these preferred fields decreased through the breeding period. Conclusions: This study found high prevalence of terrestrial foraging during early breeding as well as support for dietary switching early in the breeding season. The overall tendency for marine or terrestrial foraging was consistent within individuals, with gull identity accounting for much of the variation observed in foraging trips. Our results suggest that anthropogenic terrestrial food sources may play a role in the low breeding success of these gulls through either variation in quantity and/or quality. Finally, our study demonstrates the potential of combining data from GPS-tracking of individual animals with the 'ground-truthing' of habitat visited to elucidate the otherwise nebulous behavior of a generalist predator.
KW - Behavioral plasticity
KW - Foraging ecology
KW - Generalist foraging
KW - GPS tracking
KW - Ground-truthing
KW - Habitat use
KW - Individual repeatability
KW - Larus fuscus
KW - Lesser black-backed gull
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U2 - 10.1186/s40462-016-0078-5
DO - 10.1186/s40462-016-0078-5
M3 - Article
AN - SCOPUS:85026995263
SN - 2051-3933
VL - 4
JO - Movement Ecology
JF - Movement Ecology
IS - 1
M1 - 11
ER -