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

• Main Authors: Isaksson, Natalie, Evans, Tom J., Olsson, Olof, Åkesson, Susanne
• Format: Text
• Language: unknown
• Published: Taylor & Francis 2019
• Subjects: 59999 Environmental Sciences not elsewhere classified; FOS Earth and related environmental sciences; 39999 Chemical Sciences not elsewhere classified; FOS Chemical sciences; Ecology; FOS Biological sciences; 69999 Biological Sciences not elsewhere classified; Developmental Biology; Inorganic Chemistry; Science Policy; Alca torda; common guillemot; Razorbill; Uria aalge; uria
• Online Access: https://dx.doi.org/10.6084/m9.figshare.7638632.v1; https://tandf.figshare.com/articles/Foraging_behaviour_of_Razorbills_i_Alca_torda_i_during_chick-rearing_at_the_largest_colony_in_the_Baltic_Sea/7638632/1

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 .