Britain’s Cuckoo Population Faces Uncertain Future

New research warns that climate change is endangering cuckoos as the iconic migratory birds’ body cycles can’t adjust to global warming. 

Scientists say that it could put them as out of fashion as the 18th-century mechanical time-keeping instruments.

Lead author Dr Chris Hewson, of the British Trust for Ornithology (BTO), said that many other species are thought to be able to bring forward their arrival by adjusting their internal clocks to leave their wintering grounds sooner, but this doesn’t appear to be an option for the UK Cuckoo population.

Spring is arriving earlier each year but cuckoos can’t shift their annual hike in response.

They travel the Sahara after the arrival of West African spring rains, which have remained constant.

It means they reach European breeding grounds out of sync with the peak availability of hairy caterpillars, their favourite snack.

Dr Hewson said that migrating birds are, in general, arriving back to their breeding grounds earlier to adjust to the changing climate. Some, however, are not and their population trends are less favourable than those that do.

He said that using data from 87 satellite-tracked common cuckoos from the United Kingdom, they found the spring arrival of one such species was constrained by seasonal changes in conditions at a stopover site in West Africa.

He added that they also found evidence attempting to keep up with the demands of earlier springs at the breeding grounds results in costly trade-offs, increasing the mortality rate in early migrating birds.

The phenomenon may have implications for the survival of the globally endangered bird. Most species that breed in Europe, but spend the winter in sub-Saharan Africa have made the necessary adjustments.

Prior research has established a connection between migratory birds with fixed arrival dates and more severe population declines.

Now, Dr Hewson and colleagues have used data from the long-running BTO Cuckoo tracking programme to demonstrate why cuckoos are so vulnerable.

The study, published in the journal Proceedings of the Royal Society B, also shows the possible impact on the struggling UK population.

Cuckoos migrating to the UK leave their wintering grounds in the rainforests of central Africa in late February.

They spend a month or so fattening up in West Africa ahead of their difficult non-stop Sahara crossing.

Data collected on 87 Cuckoos tagged since 2011 show the birds must wait for the explosion in invertebrate prey brought each year by monsoons.

The Cuckoo is presently Red Listed as a Bird of Conservation Concern in the United Kingdom, due to its population decline.

Since 2011 they’ve been satellite-tracking Cuckoos to discover why they’re declining.

Common cuckoos spend their winters in Africa and migrate to the United Kingdom in the spring to breed, normally arriving in late April and early May, but the familiar birds have become much scarcer in recent decades.

To better understand why cuckoo populations were declining the BTO launched the Cuckoo Tracking Project in 2011 to tag and observe the birds during their intercontinental migration.

The team put a satellite marker as part of the tracking project. Since then, they’ve observed the cuckoo’s travels over the Sahara desert and the Ivory Coast of Africa, through France and Spain, and eventually back to Suffolk, England, where the cuckoo was first discovered.

Now, as of April 23, it’s the first bird in the Cuckoo Tracking Project to complete five migrations back to his English breeding ground.

In the past five years, it’s crossed the Sahara 10 times, soared through Africa’s Atlas Mountains and navigated Europe’s Pyrenees.