Long-term monitoring is key to understanding changes in Guillemot populations

Changes in the diet composition of Common Guillemots Uria aalge chicks on Skomer Island, Wales, between 1973 and 2017. Riordan, J. & Birkhead T.R. 2017. IBIS. DOI: 10.1111/ibi.12570. VIEW

Monitoring the diet of Common Guillemot, Uria aalge, chicks is one relatively straightforward way we can assess the state of the marine environment. We know from GPS tracking that the Guillemots breeding on Skomer Island, Wales forage within 31km of the island in the southern Irish Sea, and we know that Guillemots, like other seabirds, sample fish availability better than any human.

Further north in Britain, climate change has resulted in some dramatic shifts in seabird diet with disastrous consequences for guillemots (Wanless 2005) and other seabirds (Howell et al. 2017). Since climate change effects are likely to get worse before they get better it is important to continue to monitor accurately and consistently Guillemot chick diets. For some reason, the Skomer study is only one of a very few that records such data.

Figure 1 . Skomer Island found off the south-west coast of Wales, UK. This is one of the few places where long-term monitoring of Common Guillemots has been conducted in Britain © Tim R. Birkhead

Our long-term monitoring study of Guillemots on Skomer has made the annual recording of chick diet a key parameter, along with Guillemot numbers, survival, breeding success and the timing of breeding (Birkhead 2016; Meade et al. 2013).

The Welsh Government (Natural Resources Wales) terminated the modest, but adequate, £12K per year funding for this long-term study in 2014 (Birkhead 2014). However, the study has been able to continue (at least until the 2018 breeding season) thanks to the donations made to our Crowdfunding campaign.

This year we have launched a new campaign to try to keep the project going in perpetuity, so if you can donate and publicise the value of the project we will be very grateful.

Figure 2 The 2017 Common Guillemot ringing team. Left to Right: Ed Stubbings; Jamie Thompson; Julie Riordan; Jason Moss; Elisa Miquel Riera; Tim Birkhead © Tim R. Birkhead

A review published by Anderson et al. (2014), summarised Guillemot chick diets from around the UK collated over several different decades, but for some reason had limited data on Skomer guillemot chicks.

We have monitored the diet of Guillemot chicks on Skomer since 1973, and found that for most of this period the diet has remained fairly similar, mainly sprats with some sandeels and fewer gadids. Over the last few years there has been a noticeable increase in gadids in the Guillemot chick diet, which are a low quality fish, with low calorific value. This shift in diet may signal an important change in the marine environment, possibly linked to climate change, and if it continues, could result in a major change in the Guillemot population. The key thing is to continue the monitoring.

Figure 3 A Common Guillemot bringing a large sized gadid to feed a guillemot chick. Gadids are increasing in the diet of Guillemot chicks on Skomer which is of great concern because they are a lower quality fish compared to medium sized sprats © Tim R. Birkhead

Figure 4 A Common Guillemot with a medium sized sprat. In recent years, fewer sprats were found in the diet of Guillemot chicks © Tim R. Birkhead


References and further reading

Anderson, H.B., Evans, P.G.H., Potts, J.M., Harris, M.P. & Wanless, S. 2014. The diet of Common Guillemot Uria aalge chicks at colonies in the UK, 2006 – 2011: evidence for changing prey communities in the North Sea. IBIS 156: 23–34. VIEW

Birkhead, T.R. 2017. The point of a Guillemot’s egg. The BOU Blog, May 01, 2017. Available from: https://bou.org.uk/blog-birkhead-guillemot-eggs/ VIEW

Birkhead, T.R. 2016. Changes in the numbers of Common Guillemots on Skomer since the 1930s. British Birds 109: 651–659. VIEW

Birkhead, T.R. 2014a. Stormy outlook for long-term ecology studies. Nature 514: 405. VIEW

Birkhead, T.R. 2014b. Saving long-term studies. The BOU Blog, November 10, 2014. Available from: https://bou.org.uk/saving-long-term-studies/ VIEW

Do Lectures. (2012, June 24). The Wisdom of Birds – Tim Birkhead [Video File]. YouTube. Available from: https://youtu.be/TSJas9P4uPY VIEW

Howells, R.J., Burthe, S.J., Green, J.A, Harris, M.p., Newell, M.A., Butler, A., Johns, D. G., Carnell, E.J., Wanless, S., & Daunt, F. 2017. From days to decades: short- and long-term variation in environmental conditions affect offspring diet composition of a marine top predator. Marine Ecology Progress Series 583: 227-242. VIEW

Meade, J., Hatchwell, B.J., Blanchard, J.L. & Birkhead, T.R. 2013. The population increase of Common Guillemots Uria aalge on Skomer Island is explained by intrinsic demographic properties. Journal of Avian Biology 43: 55–61. VIEW

The Royal Society. (2017, October 18). The Seabird’s Cry [Video File]. YouTube. Available from: https://youtu.be/IBB-TL_S9Ss VIEW

Sheffield on iTunes U. (2017, Febuarary 1). Professor Tim Birkhead – Guillemot Eggs [Video File]. YouTube. Available from: https://youtu.be/eXXG0DdNwEs VIEW


Image credit

Featured image: Common Guillemot Uria aalge © T. R. Birkhead

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