Guillemots make drastic switch in diet


A recent study has shown how Guillemots have made a dramatic change to the fish species they feed their chicks on, seemingly in response to climate change.

Seabirds are key indicators of the state of the marine environment, and monitoring their diet reveals changes to the prey communities beneath the waves. A new study led by Michael Harris of the UK Centre for Ecology and Hydrology has shone light on the adaptive abilities of Guillemot, as well as shifts in the populations of prey species in the North Sea.

Between 1982 and 2019, researchers meticulously recorded the fish provisioned to chicks by adult Guillemots on the Isle of May, Fife, throughout the whole breeding season. Analysis of the huge dataset has demonstrated that Lesser Sandeel was the primary prey species in the 1980s and 1990s.

Exhaustive monitoring throughout the breeding season for nearly 40 years has shown that Guillemots now take Sprats when Lesser Sandeels become scarce (Dave Williams).

However, since then the number of Lesser Sandeels seen carried by adult birds has slumped drastically, with the auks instead delivering increasing numbers of sprats to their young. The peak number of sandeels that were brought back to feed young increasingly shifted towards the first stages of the breeding season in more recent years.

The researchers say that monitoring throughout the entirety of the breeding season was therefore crucial, as the overall change in diet might have been overlooked if fieldwork were only carried out at the beginning of chick provisioning.

The results of the study suggest that the peak availability of Lesser Sandeels has been brought forward by climate change, creating an overall mismatch between prey availability and the species' breeding cycle. However, the birds appear to have overcome this challenge by substituting sandeels for sprats once availability of the former drops off.

Ornithologists say it is important for within-season variation in diet to be taken into account when investigating long-term changes in the diet of seabirds, in order to best understand changes in food availability and the prey selection of birds.



Harris, M P, Albon, S D, Newell, M A, Gunn, C, Daunt, F, and Wanless, S. 2022. Long‐term within‐season changes in the diet of Common Guillemot (Uria aalge) chicks at a North Sea colony: implications for dietary monitoring. IBIS. DOI: https://doi.org/10.1111/ibi.13063

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