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The Mystery Of The Very Early Cuckoo

Cuckoo

In 2010 we asked visitors to our website to let us know about the first cuckoos they heard each spring. We weren’t sure whether anyone would get in touch as the usual method of reporting cuckoos is to pen a letter to The Times.

And for the first couple of years we only received a few reports. These all tended to be from people living in the south west and occurred around the 14th April which is the traditional day to hear the first cuckoo of spring.

But over the years the number has increased and we now regularly receive 100s of reports annually. What has also happened is that the reports are submitted earlier and earlier. We receive many emails from people who say they have heard and seen cuckoos in January and February and we have even had a few claims made in the December of the previous year.

The earliest reliable record of a cuckoo spotted in the UK was at Farnham, Surrey on the 20th February 1953. If the submissions we receive are correct it would seem that in the past few years that record has been broken many times over.

Tracking cuckoo migrations

In 2011 the BTO embarked on a cuckoo tracking project using solar-powered tags to track cuckoos on their long migrations to and from Africa. Although cuckoos had been ringed for almost a century prior to the kick-off of this project only 1 ringed cuckoo had ever been recovered.

On the 30th January 1930 a cuckoo ringed as a chick in Eton on the 23rd June 1928 was killed by a bow and arrow in Cameroon, West Africa. The hunter gave the ring to his wife to wear in her nose. A pastor at the local church realised what it was and reported the ring number to the British Museum.

But apart from that one cuckoo until 2011 we had no idea where cuckoos went for the winter.

The ground-breaking research by the BTO has found that cuckoos who return to the UK in spring spend the winter in the swamp forests of the Congo. They migrate mainly at night at high altitude, between 3 and 5 km above the ground. They cross the Sahara Desert in one continuous flight that can last up to 60 hours, until the 3rd night when they are able to rest for a short period and feed once more.         

The BTO also found that cuckoos take two different routes to Africa after breeding in the UK. English cuckoos tend to fly southwest via Spain and Morocco, whilst Welsh and Scottish cuckoos fly southeast via Italy or the Balkans, before converging in the Congo basin.

Cuckoos taking the southwest route leave about eight days later than those taking the southeast route but are also less likely to survive the journey before completing the Sahara crossing, even though the route was more than 10% shorter.

The impact of climate change

Despite the challenges of the African environment, most of the deaths occur in Europe, Climate change, severe droughts, and wildfires, and the decline of hairy caterpillars, one of their main sources of food are thought to be to blame. The fact that cuckoos still follow the southwest route, despite the difficulties they face, suggests that the conditions that lead to the increased mortality rate are relatively recent.

When cuckoos return to the UK in the spring they all follow a different route northwards but there is no difference in survival rates during that journey.

The BTO’s Breeding Bird Survey has found that there has been a drastic decline in the number of cuckoos in England over the last decade which correlates with the risky route cuckoos follow during their autumn migrations. However, there has also been a decline in the population in Wales and a slight increase in the population in Scotland which means it is possible that there is another factor at play

Cuckoos are parasitic which means they lay their eggs in other birds’ nests and they time their migrations to arrive back at their breeding grounds when the host birds have just laid their eggs. The main host species in the UK are dunnocks, pied wagtails, reed warblers, and meadow pipits. Of these only meadow pipits have suffered a population decline but climate change has caused the other species to start breeding earlier by about 5 or 6 days.  

This means that when cuckoos arrive back in the UK there may be fewer available nests in which they can lay their eggs. However, more research is required to find out what impact this is having on the population.

Climate change and the dependence on pesticides is also thought to have had an impact on the number of caterpillars available for the host parents to feed their massive surrogate chicks so fewer cuckoos are surviving to adulthood.

All these factors mean that the cuckoo, a classic sight and sound of spring is becoming rarer each yea, with just 15,000 breeding pairs left in the UK. So it’s quite remarkable that so many people hear and see these elusive birds all though the winter.

Winter cuckoos

When people write to us to let us know about cuckoos they have heard in the winter they often cite mild weather as the reason they have returned so early. But as far as we know the cuckoos in Africa would have no way of knowing the current temperature in the UK. And if for some reason they could, bear in mind that cuckoos can take 3 or 4 months to complete their marathon migrations. If a cuckoo arrived in the UK in January it would have had to have left Africa in October or November.

Cuckoos only leave the UK in July or August so if you do the maths it is clear they would have had to have made a super-speedy turn around which wouldn’t have given them enough time to rest and get the much needed energy they need for the arduous journey back to their breeding grounds. They would then need to hang around in the UK for a few weeks before they could breed with no access to caterpillars all the while wasting valuable energy keeping warm.

The other explanation is that they didn’t migrate at all and spent the winter here. Again, this seems unlikely and if this was the case we would expect to get cuckoo reports throughout the autumn, and so far we haven’t had a single one.

Of the 100s of reports we have received only two have been accompanied by photographic evidence.

Fieldfare
Sparrowhawk

But these birds are clearly not cuckoos.

If you’re heard a cuckoo early in the year it’s most likely to have been a collared dove. Starlings are also very good mimics of cuckoos and they are a very obvious target for hoaxers either by vocal imitation or using some sort of electronic device.

If you think you’ve heard or seen a cuckoo in the first three months of the year then the only way that the record is going to be accepted is with visual  confirmation.

One Comment The Mystery Of The Very Early Cuckoo

  1. We heard a cuckoo calling for about five minutes in Hampton Hill, suburban south west London, yesterday (May 17th).
    Haven’t heard one for 20 years – it is much quieter without planes and traffic.

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