Satellites reveal why cuckoo birds are disappearing

By Jack Fifield

The iconic cuckoo faces a new peril on its huge annual migration to the UK - being eaten by humans, according to researchers.

The findings come as the first cuckoo to arrive in the UK has been confirmed by experts as Wilfird, who arrived back in Suffolk to breed on April 22.

Dr. Chris Hewson, a senior research ecologist working on the project, said the data had ‘revolutionized’ researchers’ understanding of the migratory birds’ movements - with satellite data revealing they can travel as far northern Angola, central Africa – a distance of 7,000 km (4,350 miles) from their breeding sites.

He said: “We didn’t really know where they went before, but we’ve been able to find out they go down all the way to central Africa, some go even further into northern Angola.

“I went to Angola, we’ve sent a couple of people chasing cuckoos as we’ve called it.

“They discovered that it’s surprising how few people who live in that area know about the cuckoos.

“One of the things we know is the iconic call of the male, but they don’t seem to do that in Africa.

“They aren’t really aware of the cuckoos, even though sometimes they do eat them – I think it’s fair to say they don’t have the same cultural attachment to it that we do.

“I wouldn’t have thought they’ve particularly palatable, because they eat a lot of toxic caterpillars.

“They’re able to cope with the toxins where a lot of other animals can’t, which gives them a bit of an advantage.

“Having said that, there are subsistence hunter-gatherer cultures all through that area.

“I know in Ghana, where I've worked, the cuckoos pass through there in Spring, people will take any bird they can get hold of, to be fair, to supplement the pot.

“It wouldn't surprise me if, when they can get hold of them, people in Africa will eat them, for sure.

“I'm not really sure if that's a big problem for them, but I'm sure it definitely still happens.”

On their journeys, the migratory birds face threats including heat waves, droughts, and even hungry humans.

The British Trust for Ornithology has attached trackers to over 100 birds since launching the Cuckoo Tracking Project back in 2011.

The pioneering tracking project has also uncovered another deadly detail – birds flying via Spain are far less likely to survive the journey than those migrating via Italy.

The first bird to make it back to Britain this year was Wilfrid, an adult who arrived in Suffolk late last month following a massive intercontinental journey from northern Angola via Spain.

Many of the tracked birds have sadly died since the project began. The oldest recorded cuckoo in UK history lived to just under eight years old.

PJ, a cuckoo tagged in 2016 in King’s Forest, Suffolk, holds the record for the longest tracked bird by the project, at six years, travelling over 60,000 miles between the east of England, Spain, and as far south as the Democratic Republic of the Congo in his seven-year lifespan.

However, his tracker went dark in May 2022 following his return to the UK, where he was presumed dead, missing out on the age record.

Researchers have discovered that cuckoos taking the route to Africa via Spain are much more likely to perish than those who travel instead via Italy.

Dr. Hewson said: “I think the initial key finding is the birds took two different migration routes to go to Africa.

“Irrespective of which route they took, whether it was via Spain or via Italy, the birds all ended up in the same wintering area, which was in the western part of the Congo rainforest in central Africa.

“Then we discovered that actually, the birds that take those two different routes survive quite differently, with quite a large proportion of birds that migrate by Spain not making it to Africa.

“Far more birds in the initial sample that migrated via Italy made it all the way down there.

“We think this is partially related to conditions in Spain, in the years when droughts and wildfires have been particularly bad, none of our tracked birds have made it to Africa from Spain.

“We also think it’s partially related to conditions in the UK – birds which migrate via Spain only come from central and southern England, and we know those are the areas where conditions for cuckoos have declined the most.

“In terms of the food supplies for the cuckoos, which is largely large hairy caterpillars, those parts of England have seen the biggest decline in the availability of those foods.

“What we’re trying to work out is to what extent are the conditions in the UK versus the conditions downstream in their migration driving the difference in survival rate that we see between birds taking these two different routes, which seems to be contributing to population decline.”