Abstract
Density-dependent competition for food influences the foraging behaviour and demography of colonial animals, but how this influence varies across a species’ latitudinal range is poorly understood. Here we used satellite tracking from 21 Northern Gannet Morus bassanus colonies (39% of colonies worldwide, supporting 73% of the global population) during chick-rearing to test how foraging trip characteristics (distance and duration) covary with colony size (138–60 953 breeding pairs) and latitude across 89% of their latitudinal range (46.81–71.23° N). Tracking data for 1118 individuals showed that foraging trip duration and maximum distance both increased with square-root colony size. Foraging effort also varied between years for the same colony, consistent with a link to environmental variability. Trip duration and maximum distance also decreased with latitude, after controlling for colony size. Our results are consistent with density-dependent reduction in prey availability influencing colony size and reveal reduced competition at the poleward range margin. This provides a mechanism for rapid population growth at northern colonies and, therefore, a poleward shift in response to environmental change. Further work is required to understand when and how colonial animals deplete nearby prey, along with the positive and negative effects of social foraging behaviour.
Original language | English |
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Article number | 240708 |
Number of pages | 14 |
Journal | Royal Society Open Science |
Volume | 11 |
Issue number | 9 |
DOIs | |
Publication status | Published - 4 Sept 2024 |
Bibliographical note
We thank Emma Wood for advice on analysis and presenting results, Alice Williams, Richard Phillips and Brendan Godley for comments on the text, and the Fundamental & Applied Biogeography group at the University of Exeter led by Regan Early for feedback. Fieldwork on Grassholm was made possible with the help of Greg Morgan and Lisa Morgan and with permission from RSPB. Many people assisted with fieldwork on Grassholm, including Richard Sherley, Anthony Bicknell, Ian R. Cleasby, James Grecian, Sam Patrick, Kelly Atkins, Kylie Scales, Tim Guilford, Claudia Stauss, Sylvie Vandanabeele, Nicola Childs, Pearl Costello, Rocio Moreno, Matthew Gummery, Lisa Sztukowski, Jana Jeglinski, Matthew Carter, Matthew Nicholson, Dimas Gianuca, Rhiannon Meier, Laura Zango, Kirsten Archibald, Jacob Gonzalez-Solis, Jen Tyler, Tommy Clay, Calum Laver,Melanie Wells, Zoe Deakin, Zoe Courchene, Richard Phillips, John Arnould, Emma Dwan, Jack Wright, Georgia Bardua, Paulo Catry, Sarah Parmor and Megan Francis. For St Kilda data collection and processing we thank Stuart Murray and Maria Bogdanova, and the UK Centre for Ecology & Hydrology for funding. For help with fieldwork on Rouzic, we thank François Siorat, Mélanie Le Nuz, Clara Péron, Tangi le Bot, Sam Patrick, Françoise Amélineau, Nory El Kasbi, Thierry Boulinier and Jérôme Fort. We acknowledge the support of Point Blue Conservation Science. Tracking data from Newfoundland was supported by NSERC grants to W.A.M.
Data Availability Statement
R scripts and data are available at [78], archived at [79]. Gannet tracking data used in this study are available to request from the BirdLife International Seabird Tracking Database (https://www.seabirdtracking.org/) with the following dataset IDs: 716–725, 728–734, 955–956, 1341–1342, 1472–1473, 1475–1478, 1543, 1636, 1638, 1653, 1660, 1793–1796, 2201. Electronic supplementary material, table S1 contains additional data for the 21 gannet colonies [108]. Figure S1 shows the relationship between trip duration and maximum distance. Electronic supplementary material, table S2 gives model estimates for colonies for which more than 10 individuals were tracked. Electronic supplementary material, table S3 gives the values derived from GPS data and colonies counts separated by year.Keywords
- central place foraging
- coloniality
- species distributions
- bio-logging
- predator–prey
- seabird