By measuring body mass and wing length of adult Atlantic Puffins on their breeding grounds and in their wintering areas near the Faroe Islands, researchers have estimated the seasonal changes in body mass for two populations breeding in Norway and Scotland respectively.

Data from geolocators and hunted puffins

For pelagic seabirds, which generally have small clutches and invest more in adult survival than in reproduction, the build-up of fat reserves in the body after the breeding season is important to increase the chances of surviving through the winter, when both weather and food availability may be demanding for long periods. How much mass they actually gain is hard to assess, since recapturing the individuals that were weighed on the breeding grounds at sea in winter is normally impossible. In recent years, mapping seabird movements using geolocators has provided helpful information on where different populations go outside the breeding season. We now know, for example, that many Atlantic Puffins that breed in North-Norway and in SE Scotland spend time near the Faroe Islands in winter. By comparing body mass and wing length of puffins caught in the breeding colonies with corresponding measurements of puffins hunted in the Faroes during the winter, researchers have now estimated the change in body mass of puffins between the breeding and wintering periods more accurately.

Gaining weight in the autumn

Puffins that were shot in winter weighed on average 20-30% more than when breeding in Scotland and North-Norway. Among the birds hunted in the wintering area were three ringed individuals that had also been weighed and measured on the breeding grounds, and their mass change corresponded well with the changes estimated on the population level. The study shows that between the chick-rearing in the summer and wintering in the Faroes, puffins gain at least twice the mass they normally lose between incubation and chick-rearing during the breeding season. This knowledge is valuable with regard to explaining major die-offs and understanding the birds’ vulnerability to the increasing number of extreme weather events following climate change.

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Contact person: Tycho Anker-Nilssen, NINA

From they leave the colony after breeding till they reach the Faroes in winter, Norwegian and British puffins add 20-30 % fat.
Photo: Tycho Anker-Nilssen