Articles | Volume 13, issue 2
Research article
25 Apr 2017
Research article |  | 25 Apr 2017

Seabirds as samplers of the marine environment – a case study of northern gannets

Stefan Garthe, Verena Peschko, Ulrike Kubetzki, and Anna-Marie Corman

Abstract. Understanding distribution patterns, activities, and foraging behaviours of seabirds requires interdisciplinary approaches. In this paper, we provide examples of the data and analytical procedures from a new study in the German Bight (North Sea) tracking northern gannets (Morus bassanus) at their breeding colony on the island of Heligoland. Individual adult northern gannets were equipped with different types of data loggers for several weeks, measuring geographic positions and other parameters mostly at 3–5 min intervals. Birds flew in all directions from the island to search for food, but most flights targeted areas to the (N)NW (north–northwest) of Heligoland. Foraging trips were remarkably variable in duration and distance; most trips lasted 1–15 h and extended from 3 to 80 km from the breeding colony on Heligoland. Dives of gannets were generally shallow, with more than half of the dives only reaching depths of 1–3 m. The maximum dive depth was 11.4 m. Gannets showed a clear diurnal rhythm in their diving activity, with dives being almost completely restricted to the daylight period. Most flight activity at sea occurred at an altitude between the sea surface and 40 m. Gannets mostly stayed away from the wind farms and passed around them much more frequently than flying through them. Detailed information on individual animals may provide important insights into processes that are not detectable at a community level.

Short summary
We investigated how the largest seabird of the North Atlantic, the northern gannet, uses the southern North Sea as its habitat to search for food. We deployed small GPS trackers on the birds that recorded the birds' movements in detail. Birds were away from the breeding colony mostly for 1–15 h and up to 80 km distance to find prey for their chicks and themselves. To obtain food, they dove frequently to depths of 1–3 m, with a maximum of 11 m.