On Hearing the First Cuckoo in Spring.
New for 2020 is our Conservation Documentary Award sponsored by Gitzo. Paul Sterry gives a guide on the sort of entry this award seeks to attract with this piece on the Cuckoo.
The Cuckoo is arguably the UK’s most familiar summer visitor but according to the British Trust for Ornithology (BTO) since the early 1980s numbers have declined by a staggering 65%. If Frederick Delius were alive today and living in southern England he might soon have to compose a new tone poem ‘On hearing the last Cuckoo in Spring’ to reflect this downward trend. The reasons for the Cuckoo’s woes are unclear but BTO research is helping unravel the story and identify potential factors.
Having spent the winter months in Africa, Cuckoos arrive back in the UK from mid-April to early May. The first job of a male is to advertise its presence with the iconic and onomatopoeic song; once widespread and familiar nowadays this is an increasingly rare sound in southern Britain away from a few Cuckoo hotspots. Photo ©Paul Sterry.
Hairy caterpillars feature heavily in an adult Cuckoo’s diet and they are not put off by the irritant bristles that deter other bird species. However, moths such as the Drinker Euthrix potatoria, whose larvae by rights should be an important food source in southern England, appear anecdotally to have declined significantly in recent years. The caterpillars feed on coarse grasses in damp, agriculturally ‘unimproved’ meadows. It is hard to imagine that habitat degradation (through land drainage, herbicide application and rank grass seeding for example) has not played its part in the moth’s downfall. In southern England at least, away from nature reserves and heathlands, you have to wonder what on earth can Cuckoos find to eat these days? Photo ©Paul Sterry.
Cuckoos are nest parasites and have evolved to time their migratory arrival in the UK to match the breeding season of host species. The main targets for egg-laying here are Meadow Pipit, Dunnock, Pied Wagtail and Reed Warbler. Individual birds tend to be species specialists: for example, those raised by a Reed Warbler are likely to return to reedbed habitats and in turn target Reed Warblers for nest parasitism. Photo ©Paul Sterry.
In response to global warming the average breeding seasons of Dunnock, Pied Wagtail and Reed Warbler have shifted forward by about 5-6 days in recent decades according to BTO research. However, phenological changes may not be a root cause of the Cuckoo’s decline and in fact earlier Reed Warbler breeding may actually be a benefit. These conclusions can be drawn from years of extensive research, including work undertaken by BTO staffer Dr Dave Leech who helped with the capture of this image. Photo ©Paul Sterry and Rob Read.
Since 2011 the British Trust for Ornithology has been satellite-tracking Cuckoos to monitor their migration routes and discover where precisely they go in winter. The results have been informative and revelatory in equal measure. Here, journalist Mike McCarthy releases a bird named ‘Clement’, one of the first satellite-tagged Cuckoos. Photo ©Andy Clements.
An evaluation of BTO research to date strongly indicates that climate change may be an important factor in the Cuckoo’s decline. Specifically the information reveals the need to understand how successful Cuckoo migration is linked to and dependent upon the drought-ending rains of the weather frontal system known as the Inter Tropical Convergence Zone. Satellite tagging. ©Paul Sterry.