‘We’ve underrated what these birds can do’: the secret life of Skomer’s guillemots

For the past 52 summers, Tim Birkhead has inched along the vertiginous cliffs to count, ring and observe the guillemots that nest in their thousands on the Welsh island of Skomer. His life’s work offers unrivalled insight into seabirds in an era of climate breakdown and also reveals the unexpectedly colourful lifestyles of these gregarious birds.

Having crowdfunded his research for the past decade, the emeritus professor is now seeking to raise £125,000 to support his guillemot study in perpetuity.

“Long-term ecological studies like mine are particularly valuable in tracking the impacts of climate, fishing and disease on seabird populations. In the future our study will undoubtedly help answer questions we haven’t yet even formulated,” Birkhead said. “My study happens to be incredibly good value for money, costing £12,000 each year. It also provides valuable experience and training for young research scientists.”

When Birkhead, 73, was first dispatched to the uninhabited island as a young PhD research student in 1972, he was expected to chronicle the decline of the guillemots, whose breeding population had crashed from 100,000 in the 1950s to just 2,000 – largely attributed to oil spills in the region.

Instead, he watched Skomer’s guillemots steadily recover, increasing their numbers by 5% each year to nearly 30,000 today.

During the nesting season, 250 bird lovers a day visit Skomer to admire its seabirds. “I would say that 99.5% of people come to see the puffins and nobody gives a monkey’s about guillemots,” Birkhead said. “I understand why people love puffins, they are beautiful and comical, but because I’m interested in behaviour as well as ecology, I hit the jackpot with guillemots. They live in dense groups and their social behaviour is so complicated and so rich. There’s gossip, arguments and infidelity – sitting in a hide on Skomer and watching a guillemot ledge is like watching an episode of EastEnders.”

Birkhead has made some fascinating discoveries over the years. Guillemots are long-lived birds – his oldest reached 39 – and they pair for life. But their monogamous natures are tested by neighbours. Birkhead undertook DNA fingerprinting to see what proportion of chicks were fathered by the male bird in the neighbouring nest, and discovered that 7% of chicks are the result of “extramarital” matings.

On one occasion, he was in a homemade hide just a metre away from a bird incubating an egg when it began its greeting call. Birkhead scoured the horizon with his binoculars before picking up a tiny speck in the air almost 1km away. “And bugger me, it landed by this bird that has been calling. The bird recognised its partner, where I just saw it as a speck.” This experience inspired his book, Bird Sense, which explores how birds interpret the world. “We have so underrated what these birds can do,” he said.

Guillemots lay just one particularly beautiful and unusually pear-shaped egg each year. For years, ornithologists have debated the evolutionary purpose of this “pyriform” egg shape: some say it enables the egg to spin on its axis, while others suggest it ensures the egg rolls in an arc, reducing the likelihood of it falling off the narrow ledges where guillemots lay their egg, without any protective “nest” around it.

But Birkhead realised both theories were wrong. Any egg shape can spin, and the arc that a pyriform egg rolls in is wider than most cliff ledges. When he placed a guillemot egg on a steeply sloping rock, “to my amazement, it just sat there. I replaced it with the razorbill egg which simply wouldn’t stay put”.

Because the guillemot egg has a long straight edge towards a point, and this rests on the ground, there is more friction, reducing the likelihood that it will move.

So the shape does stop the egg slipping off narrow ledges and, more importantly, this enables guillemots to nest close to one another even on uneven cliff edges. Observing the colony’s behaviour as it has grown over the decades, Birkhead realised that the birds rely on safety in numbers and nesting crammed together protects their eggs and chicks from predatory gulls.

A guillemot egg.
A guillemot egg. Photograph: Murdo MacLeod/The Guardian

Globally, seabird numbers have fallen by 70% since the 1950s, and in northern Britain most seabird populations have had significant declines in recent years. More southerly populations – including Skomer – have bucked that trend but after more than 40 years of a steadily growing colony, bird flu struck the colony last summer, leaving the 2023 population down 8%. Birkhead said bird flu was “my worst nightmare”; he fears the impact could be much greater because so many birds die out of sight at sea. “It’s hard to judge what the long-term prospects are. We could see some catastrophe triggered by climate change. This year might be that tipping point.”

The reason for the north-south divide in the British seabird population trend – with northern populations declining with the vanishing of fish stocks – is not fully understood.

“There’s no simple explanation,” Birkhead said. “It tells you that different waterbodies are behaving in different ways [in response to climate] and the birds that live in those waterbodies are operating in different ways. I’d love to know.”

Global heating is causing hotter, wetter and stormier weather, with “unseasonal” storms now striking Skomer during the breeding season and causing “seabird wrecks” – mass mortality. “Seabirds have evolved to cope with those occasional disasters – they are very long-lived,” said Birkhead. “But if those wrecks happen too frequently, it’s going to have a detrimental effect.”

His studies show that Skomer’s guillemots have moved their breeding season two weeks earlier because of climate change. They can bounce back from human-made and natural disasters surprisingly quickly – one reason being that the birds usually do not start breeding until they are seven years old, but when populations are wiped out four or five-year-old birds will step up and start breeding.

But Birkhead fears that in the long-term the population will suffer because of such disruption, and it is not yet known how the climate crisis will affect fish stocks in southern British waters.

“Because of what’s happening further north, I’ve always thought there will come a point when things go pear-shaped for the guillemots of Skomer,” he said. That is another reason Birkhead hopes he can raise enough money to fund his studies in perpetuity.

“It doesn’t look great for any wildlife. Human-made factors are eating into our natural ecology, it’s just so sad,” he said.

Climbing the cliffs to study seabirds is hazardous – a falling rock the size of a VW Beetle once rolled down the cliff and landed on a ledge 2 metres from Birkhead – but he is determined to continue to help his research scientists on Skomer for as long as he can.

“I am passionate about Skomer,” he said. “In May the entire island top is covered in bluebells. As you get off the boat you are hit by their scent. Six weeks later the bluebells have been replaced by acres of pink campion. It’s stunningly beautiful.”