Little is known about how seabirds catch their food outside the breeding season but using modern technology, researchers at the University of Liverpool and the Centre for Ecology & Hydrology have gained new insight into their feeding habits.
Seabirds, including puffins, are often elusive and spend much of their lives at sea – particularly outside the breeding season – and feed exclusively there.
Using depth recorders, researchers compared the feeding behaviour of puffins with two closely related species, guillemots and razorbills, to find out how deep and for how long they dive during the non-breeding period.
Researchers fitted loggers to seabirds breeding on the Isle of May in south-east Scotland, where the Centre for Ecology & Hydrology (CEH) carries out long-term ecological studies into the seabird colonies. These birds were then recaptured the following breeding season, when they returned to land again after months away at sea.
Puffins are excellent divers and, in a similar way to penguins, use their wings to ‘fly’ underwater to catch their prey. Yet the study found that despite this great diving ability, both common guillemots and razorbills can dive even deeper and for longer than puffins can.
As well as these important species differences, the research – published in the Journal of Avian Biology – also found that the diving of all three species changed over the course of the year.
Ruth Dunn, a PhD student at the University of Liverpool, who led the study, says: “In this study we found that after the birds left the breeding colony they didn’t dive as deeply as expected, often reaching depths of less than 15 metres, possibly because they were catching different prey. Despite these shallow dives, birds were very busy, particularly in mid-winter when they were working harder than in the autumn and spring.”
These insights into the winter feeding behaviour of puffins are extremely valuable since this species has shown marked declines in recent years – Dr Francis Daunt
Researchers also found some birds were busier than others. Immediately after leaving the breeding colony, guillemot and razorbill fathers both dived more than their female partners. This is because male parents accompany their chicks to sea and continue to feed it for several weeks after the breeding season has ended. Male birds therefore had to dive more frequently in order to catch enough fish not only to feed themselves, but also to meet the nutritional demands of their growing chicks.
In contrast with the other species, puffin chicks go to sea on their own. Therefore, the adults dive at a similar intensity throughout the post-breeding period, because there is not another hungry seabird beak to feed.
Dr Francis Daunt of CEH, a co-author of the study, adds: “These insights into the winter feeding behaviour of puffins are extremely valuable since this species has shown marked declines in recent years, linked to higher mortality rates of adult birds in certain winters. These data show the middle of winter is when birds are working hardest, which suggests over-winter survival may be closely linked to the ability to find sufficient food.”
Ruth E. Dunn , Sarah Wanless, Jonathan A. Green, Michael P. Harris, Francis Daunt. 2019. Effects of body size, sex, parental care and moult strategies on auk diving behaviour outside the breeding season. Journal of Avian Biology. DOI: 10.1111/jav.02012
The study received funding from the Natural Environment Research Council (NERC), Defra and the RSPCA.
CEH's studies of the puffin colony on the Isle of May are being featured in BBC Radio 4's Planet Puffin series. You can listen again to previous episodes via BBC Sounds.