BBC Blogs - Springwatch - Tracking cuckoos with BTO

Tracking cuckoos with BTO

Hannah StitfallSpringwatch Team

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Cuckoos are often heard before they are seen and for some are certainly the first sign of spring! However since the 1980s these cunning parasitising migrants have suffered severe declines - their numbers have dropped by 65%.Overwintering in central Africa they migrate each year to the UK to breed, and it is thought that some birds may travel nearly 2000 miles in a single flight. But with the species experiencing such huge declines, it's raised the question of what is happening to them en route?

A recently tagged cuckoo which will hopefully reveal new insights on their migration route

This issue had been a mystery to ornithologists for sometime, but the British Trust for Ornithology (BTO) have started a fantastic initiative by tagging and monitoring their migration route. To date BTO have successfully tagged 50 birds and so far findings have revealed the different routes taken by the birds, as well as revealing the risks they face.

The BTO team have been busy out in the field collecting more data.

The guys at BTO have also sent us this fabulous (and very rare) footage showing some outstanding cuckoo behaviour!

Here you can see a hepatic cuckoo. It's a female but is a ‘rufous’ morph, so instead of being grey it is reddish-brown. What is also interesting about this footage is that the female isn’t parasitising the nest for her own eggs, she is in fact predating it.

Females will sometimes do this as it serves them not one, but two purposes. Firstly the egg provides the female with a good source of calcium and protein, which aids her in producing her own eggs. This also forces the reed warbler - one of the cuckoos favourite host species - to lay another clutch of eggs, effectively resetting the clock for the cuckoo to lay her eggs at exactly the right time.

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A hepatic cuckoo predating upon a nest

To find out more about the BTOs cuckoo project and how you can get involved click the link below.

BTO Tracking Cuckoos to Africa...and back!