Cuckoos face uncertain future in Britain

Cuckoos face uncertain future in Britain as global warming means they are no longer arriving in the UK at the right time to raise their young

• Spring is arriving earlier each year but cuckoos can’t shift their annual trek 

Climate change is endangering cuckoos as the iconic migratory birds’ body cycles can’t adapt to global warming, warns new research. 

It could put them as out of fashion as the 18th Century mechanical time-keeping instruments, say scientists.

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.’ 

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

They cross the Sahara after the arrival of west African spring rains – which have remained constant. 

Climate change is endangering cuckoos as the iconic migratory birds’ body cycles can’t adapt to global warming, warns new research

It could put them as out of fashion as the 18th Century mechanical time-keeping instruments, say scientists

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

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

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. 

‘Using data from 87 satellite tracked common cuckoos from the UK, we find the spring arrival of one such species is constrained by seasonal changes in conditions at a stopover site in West Africa.

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.’ 

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

Previous research has shown a link 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 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. 

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.  

The reasons for this have so far remained unknown, with reduced breeding success appearing to play a surprisingly unimportant role.

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

This increased mortality could be one mechanism through which populations are impacted. 

Providing better quality habitat at strategic locations along cuckoo migration routes might help the birds complete their epic journeys in a more timely and less energetically costly way, helping them adapt to our changing climate.

Dr Hewson said: ‘It is fantastic to have this new insight into what determines the spring arrival of our Cuckoos, 12 years after the tracking project first allowed us to follow their return from central Africa.’ 

He added: ‘Understanding why these are not arriving back earlier – and the possible costs that individual Cuckoos pay for trying to do so – will help us to best direct efforts of flyway restoration that may allow them to make their migrations in a more timely and successful fashion.’ 

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