BTO: Cuckoos are on their way ‘home’

Cuckoo by Edmund Fellowes/BTO ANL-140228-134910001
Cuckoo by Edmund Fellowes/BTO ANL-140228-134910001
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While the first hints of spring are already being noticed here, with a few warmer days triggering the emergence of overwintering butterflies, spring proper still seems a long way off.

Despite this, cutting-edge technologies are revealing how, for some birds at least, the approaching spring is already well under way.

The British Trust for Ornithology’s (BTO) satellite-tagged cuckoos, which have spent the winter in the forests of the Congo, have already started their northward migration, a journey that will take them first into West Africa (to Ghana and Burkina Faso) before the birds turn north to cross the Sahara.

That we can track the start of spring from such a distance is a remarkable achievement, and the lives and journeys of these cuckoos are already teaching us a great deal. By learning about the cuckoos’ wintering grounds, the routes that they take on their journeys and the sites at which they stopover to refuel, we are beginning to identify the places and habitats that will need to be conserved if we are to halt the decline in fortunes of this harbinger of summer. Cuckoo numbers in the UK have declined by 73 per cent since the mid-1960s, with most of this decline occurring since the early 1990s and with the greatest losses noted across southern and eastern England. While the reasons for the decline remain unclear, the current BTO work on cuckoos should go some way to identifying the possible factors behind the declines.

The satellite tags have also enabled the BTO researchers to follow individual birds over several years, revealing – as in the case of cuckoo DD24004 (christened ‘Chris’ by the researchers) – that birds will use the same routes and wintering areas each year. The tags have also revealed just how little time these birds actually spend within the UK. Last summer for example, Chris, a male cuckoo, arrived here on May 5 but had left again by June 22. While we may think of these birds as ours, they are only ours for a small part of their year. The female cuckoos remain here for longer, though only for long enough to deposit their eggs into the nests of reed warblers, meadow pipits and other unfortunate hosts. The resulting chicks will make their first southward migration never having had any contact with their parents, or indeed with any other cuckoo, something that is equally amazing when you consider the journey that lies ahead of them.

There used to be a tradition that The Times would publish a letter announcing the first cuckoo of spring, heard by a reader. Today, at least some of our cuckoos announce their own arrival, thanks to the tiny satellite tags they are carrying. You can follow the progress of the spring cuckoo migration via the BTO’s website