In one of the world’s longest running studies of its kind, a scientist has revealed how climate change has led to mass mortality events, altered breeding times, and how bird flu is devastating the population. The scientist has dedicated his life to studying seabirds.
population of guillemots
Professor Tim Birkhead, from the University of Sheffield’s School of Biosciences, has been studying a population of guillemots off the coast of the UK for the last 50 years.
He started the study as a PhD student in 1973 and is now publishing it as an emeritus professor at the same university half a century later. The study is one of the most important in understanding how UK seabird populations are being affected by climate change and disease, as a second wave of bird flu is sweeping across the UK.
The study’s findings reveal that avian flu is taking a toll on the guillemot population, which resides on Skomer Island, situated off the Pembrokeshire coast. Skomer Island is the most important seabird site in Southern Britain.
The disease has claimed the lives of thousands of guillemots, and the Sheffield scientist is concerned that it poses a looming catastrophe for these birds. Guillemots, who have been breeding on Skomer for centuries, have already faced challenges from oil pollution, climate change, and now, avian flu.
Professor Tim Birkhead, Emeritus Professor in the University of Sheffield’s School of Biosciences, said: “The current bird flu outbreak is potentially disastrous for Skomer’s guillemot population. Thousands have been killed so far and it looks like things may get worse.
“It is heartbreaking to see them being so badly affected as Skomer Island is one of the most important seabird sites in the UK – it homes a major proportion of the total number of guillemots and other seabirds in the whole of Britain.”
“If avian flu continues to spread, this could turn into one of the biggest disasters to hit the UK’s seabird population.”
How climate change has affected guillemots
The 50-year study has found that, aside from avian flu, the guillemot population now breeds over two weeks earlier than it did in the 1970s. This change in breeding timing may be related to climate change, which has altered the distribution and abundance of the guillemot’s fish prey in recent decades.
More extreme weather events, especially winter storms, caused by climate change, have resulted in mass mortality events – known in the seabird research community as wrecks. In 2014, extreme weather off the coast of Wales caused a sharp increase in guillemot deaths.
Climate change means that extreme weather is now more frequent during the guillemot’s breeding season and has a major impact on breeding success. In May 2021, two major storms directly caused the loss of many guillemot eggs and reduced breeding success.
Professor Tim Birkhead says, “I’ve witnessed how climate change is affecting how guillemots live over the last 50 years. Changes to the climate are making it more difficult for them to breed, find food, and increase the number of events that threaten the population’s very existence. Mass mortality events, or wrecks, have always occurred but they were once rare and seabirds have evolved to cope with them, but now their increased frequency is very worrying.”
How the guillemot population works
Professor Birkhead’s long term study has also shown that the guillemot population of Skomer works as a self-sustaining system and that their social life is complex and fascinating.
Professor Birkhead said, ‘In 1973, I soon realized that I needed to work out why and how guillemots breed in such close physical contact with their conspecific neighbors – at an average of about 20 pairs per square meter – at the colony, as some seabirds spend much of their breeding season alone in a burrow, whereas guillemots typically breed out in the open, continuously interacting with their surrounding friends and family.'”
Guillemots lay their eggs together on open cliff ledges and defend them as a group from predatory gulls and ravens. Professor Birkhead demonstrated how guillemots successfully produce chicks by bunching together, breeding synchronously, and sitting tight in the face of a predator. His work shows that sitting tight in a dense group is extremely effective as a defence against gulls and corvids.
Guillemots are socially monogamous, forming long-term pair bonds, but males in particular rarely pass up the opportunity of copulating with a neighbour’s partner, usually only when the neighbouring male is absent.
Males initiate most extra-pair copulations and they can only succeed if the female co-operates. The monitoring revealed that when a male witnesses an attempted extra-pair copulation on his partner, his aggression becomes unrestrained. In 2001, Professor Birkhead had found, using molecular methods, that a male other than the one assisting in rearing had fathered approximately seven per cent of the chicks.
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