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Foraging behaviour of Razorbills Alca torda during chick-rearing at the largest colony in the Baltic Sea

Author:
  • Natalie Isaksson
  • Tom J. Evans
  • Olof Olsson
  • Susanne Åkesson
Publishing year: 2019-01-28
Language: English
Pages: 11-21
Publication/Series: Bird Study
Volume: 66
Issue: 1
Document type: Journal article
Publisher: British Trust for Ornithology

Abstract english

Capsule: Foraging behaviour in the Razorbill Alca torda during breeding was similar to that found elsewhere, aside from dive shape. Aims: To investigate the foraging behaviour of Razorbills during the breeding season at the largest colony in the central Baltic Sea. Methods: A combination of global positioning system (GPS) and time-depth recorder (TDR) devices were used on Razorbills breeding on the island of Stora Karlsö, Baltic Sea, during the chick-rearing period. Results: Five GPS tracks and nine TDR logs were retrieved from 12 Razorbills, and 7399 dives were analysed. Razorbills foraged south and southwest of the colony. Maximum and mean (±sd) foraging range from the colony was 72.7 km and 13.1 ± 13.5 km, respectively. Mean dive depth (15.3 ± 2.4 m) and duration (53.1 ± 8.5 s) were similar to those of a more southern Baltic Sea Razorbill colony. Dive depth had a bimodal distribution, with 70% of dives deeper than 10 m and 30% shallower than 10 m. There was a clear diel foraging pattern with 89% of dives occurring during daytime and a higher proportion of shallow dives at night. Unexpectedly, dives were primarily U-shaped. The Razorbills spent 31% of their overall time activity budget flying or diving. Conclusion: Aside from dive shape, foraging behaviour was consistent with that reported at other colonies of Razorbills. Inconsistency in dive shape may be due to a bimodal foraging strategy, local prey behaviour or competition with the Common Guillemot Uria aalge.

Keywords

  • Zoology

Other

Published
  • ISSN: 0006-3657
Susanne Åkesson
E-mail: susanne [dot] akesson [at] biol [dot] lu [dot] se

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