Cuckoo’s clocks are going cuckoo – because of climate change, experts warn

Cuckoo’s clocks are unable to keep up with climate change, new research warns.

The birds spend the winter in central Africa, before travelling north to western Europe to herald the arrival of spring.

But researchers believe their internal body cycles – which determine when they set off on their epic journey – are unable to adjust to the fact spring is arriving increasingly earlier.

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

Lead author Dr Chris Hewson, of the British Trust for Ornithology (BTO), said: ‘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.’

The phenomenon may have implications for survival of the bird.

Most species that breed in Europe, but spend the winter in sub-Saharan Africa have made the necessary adjustments, arriving at their breeding grounds earlier to adapt to climate change.

Previous research has shown a link between migratory birds who are unable to change their arrival dates and severe population declines.

Now, Dr Hewson and colleagues have used data from the long-running BTO Cuckoo tracking project to reveal 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 arduous non-stop Sahara crossing.

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

The birds now reach their breeding grounds out of sync with their primary foodstuff

Although the timing of that annual event remains unchanged, spring is arriving earlier in Europe.

It has led to a mismatch between the Cuckoos’ arrival, the peak availability of the caterpillars they rely on for food and the breeding cycles of the host species they parasitise.

Species that are unable to shift the timing of their arrival on their breeding grounds are known to be declining more quickly than those that can.

Results suggest cuckoos are exposed to a greater risk of death as they race to arrive back on their breeding grounds in time.

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

‘We also find 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.’