If access to a preferred prey is poor, would it be most profitable to expend energy finding another area where the prey is more accessible, or would it be better to stay and switch to a less nutritious food? Using light sensors and stable isotopes, researchers have now studied how Atlantic puffins and razorbills respond to changes in environmental conditions in the North Sea outside the breeding season.

Contrasting conditions

The marine environment is dynamic and may change significantly between years. Knowing how seabirds respond to such changes is a key element in understanding their ecology. Seabirds are mobile predators which can choose to move if access to food is poor. Alternatively, they can change their diet. This choice reflects the balance between risks and benefits associated to resource intake, energetic costs and physiological demands. The razorbill and Atlantic puffin are two species which often breed sympatrically, and they both hunt for nutritious prey such as sand eel, sprat and herring. We know little about how these birds respond to changes in environmental conditions outside the breeding season. The North Sea winter of 2007/2008 was harsh and studies from Isle of May on the coast of Scotland showed that survival rates of razorbills and puffins were low that particular winter. In contrast, their survival was very good during the favourable winter of 2014/2015. By using light sensors and stable isotopes from feathers, researchers sought to find if these differences in survival rates between the two winters were associated with the wintering areas in the North Sea, and whether or not the birds’ diet in their wintering areas during moult could be related to prey availability.

Different strategies

It turned out that, almost regardless of environmental conditions, puffins spent the winter in the northwest part of the North Sea. In 2007/2008, the availability of sand eel, sprat and herring was low, and the puffins fed at a lower trophic level, probably on snake pipefish – a species much poorer in energy. In the favourable 2014/2015 winter, razorbills overwintered southeast and northeast of Scotland where food access was good. But in the harsh winter of 2007/2008, they moved further south in the North Sea, to an area where the abundance of sand eel, sprat and herring was better, thereby maintaining their normal diet. Razorbills also maintained a higher survival rate than puffins in 2007/2008. The study showed that different species may choose different feeding strategies under varying environmental conditions, and this should be kept in mind when conservation plans are laid for species that migrate.

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Contact person: Kjell Einar Erikstad, NINA

Atlantic puffins and razorbills choose different feeding stratiegies when their preferred prey becomes scarse in the wintering areas.
Photo: Erlend Lorentzen