On hearing the last Cuckoo in Spring?

By Paul Sterry

If Frederick Delius were alive today and living in southern England, he might soon be forced to compose a new tone poem entitled ‘On hearing the last Cuckoo in Spring’ to reflect the species’ slide towards oblivion. According to the report entitled Birds of Conservation Concern 4, it is a Red List species because of recent population declines. Fewer than 15,000 birds are thought to breed here today; the number is declining year-on-year, and the Cuckoo has disappeared from many of its former haunts.

The song of the Cuckoo is an iconic but increasingly rare sound in the countryside of lowland England. Copyright Paul Sterry/Nature Photographers Ltd

Half a century ago, a now-defunct local paper in north Hampshire – the Hants & Berks Gazette – regularly published letters from readers when they heard the first Wryneck Jynx torquilla of spring; the piping territorial call of this unusual migratory woodpecker appears to have been very much a feature of mature gardens and orchards in this part of England. At the same time, at the national level, letter-writers to The Times newspaper would compete to report the first Cuckoo of spring; 50 years ago that would have been around Primrose Day, April 19th, but as the years went on and the climate warmed the date became earlier – evidence of Phenology at work – and the reports fewer. Sadly, these days the Wryneck is to all intents extinct as a breeding species in southern England, and indeed the UK as a whole. And unless, there is a marked change in its fortunes, there is every chance the Cuckoo is heading in the same direction.

An adult Reed Warbler feeding a young Cuckoo in its nest.

Paul Sterry/Rob Read/Nature Photographers Ltd

The Cuckoo is a migratory nest-parasite whose precise distribution is dictated by the breeding range and occurrence of the songbirds it uses as hosts; classic examples include Meadow Pipit, Dunnock, Pied Wagtail and Reed Warbler. The host species in whose nest a female Cuckoo will lay is genetically pre-determined – the same species in which she was raised. But Cuckoos don’t get everything their own way and there is a continual battle between host and parasite. As a general rule, Cuckoos try to mimic the colour and markings of the host's eggs, to avoid them being identified as impostors and ejected. It seems that some species have learnt to recognise a Cuckoo’s egg and will often reject it immediately (Pied Wagtail for example), while others such as Reed Warbler fail to spot the difference. It’s a bit of a mystery as to why Cuckoos parasitize Dunnocks successfully but appear to make no attempt at egg-mimicry.

Individual female Cuckoos are nest host specific, which reflects in the appearance of their eggs. Here we see Cuckoo eggs alongside host eggs from the nests in which the egg in question was laid.

Although the decline in Cuckoo numbers across the species’ huge European and Asian breeding range is subtle, in the UK it is little short of catastrophic. The species is (or perhaps was) arguably the UK’s most familiar summer visitor and formerly widespread in the English countryside in spring. But according to the British Trust for Ornithology since the early 1980s numbers have declined by a staggering 65%. The reasons for the Cuckoo’s woes are unclear but BTO research, including satellite tracking, is helping unravel the story. It looks like a range of factors may be at play: habitat loss and degradation affecting where Cuckoos occur at the local level; and climate change impacting the population as a whole. But why the appalling decline in lowland England? With a diet of insects and hairy caterpillars a favourite, and nest hosts that also feed on insects, you have to ask what can they possibly find to eat in the industrially farmed, pesticide-laden 21st Century English countryside? Green it may be, but hardly pleasant if your diet comprises primarily invertebrates.

The Cuckoo is a long-distance migrant and radio-tracking by the BTO confirms that most British birds winter in West Africa. There, and on migration, they face climatic threats (changing weather patterns, for example) that have been linked to global warming and climate change. Copyright Paul Sterry/Nature Photographers Ltd

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