During egg-laying and chick-feeding, seabirds rely on a ready access to food resources, and the size and numbers of eggs laid depend on the availability of nutrient-rich prey. Data modelling shows that an influx of warm water masses from the Atlantic into the Barents Sea has negative impacts on egg production in black-legged kittiwakes in NE Norway.

Seabirds use a lot of energy in the production of eggs at the same time as they also attend to other resource-draining tasks, such as nest building and territorial defence. To succeed in all activities, the birds need to increase their uptake of energy. The physiological preparations for egg production, incubation and chick rearing often start long before the eggs are laid, and the birds are therefore sensitive to changes in food availability prior to the breeding season. This is indeed the case for black-legged kittiwakes, which work at or near their energetic ceiling in periods of peak energy demand. Researchers have found large variations in egg and clutch size in the kittiwake colony on Hornøya, Norway, and by means of data modelling, they have tried to identify environmental causes for the observed variation.

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Influx of warm, Atlantic water to the Barents Sea in winter and autumn one and a half years before egg-laying had a negative effect on egg investment ability in the kittiwakes and explained most of the variation in egg production. The mechanism behind this might be that capelin, which is an important prey species for kittiwakes, is driven northwards as a result of the ocean warming, and thereby becomes unreachable for the kittiwakes breeding at Hornøya. A continued warming of the Barents Sea is therefore considered to be detrimental to the black-legged kittiwake population in the region.

Contact person: Rob Barrett, Tromsø Museum

The size and numbers of eggs produced by a kittiwake during the breeding season depends on the prey availability in the period prior to egg-laying.
Photo: Rob Barrett