Willow warblers like to play it cool
The lilting birdsong of the willow warbler, with its cascade of descending notes, always reminds me of the Wild West rather than the British countryside.
Whenever the little birds pour out spring refrains, I am taken back to an age of Saturday mornings spent at the cinema, and black and white cowboy films.
Only on my first trip to California’s high sierras did I discover how the tiny warblers that provided the soundtrack to my formative years birding in the Home Counties share a near identical song to American canyon wrens.
How two species whose range is separated by the Atlantic and the vast hinterland of the United States can pour out remarkable cover versions of their respective territorial proclamations is one for students of convergent evolution.
Modern TV Westerns still throb to the beat of howling wolves and yodelling canyon wrens but, sadly, the song of the willow warbler is becoming a rare sound across parts of Britain.
Scientists from the British Trust for Ornithology (BTO) are highlighting how willow warblers are a casualty of manmade climate change, with rising temperatures creating a mismatch between nestlings’ food needs and insect availability.
Using data produced by volunteers for the Breeding Bird Survey, BTO researchers have charted the fortunes of both willow warblers and the closely related chiffchaff.
Analysis shows willow warbler numbers fell by 41% across the UK between 1994 to 2018, but in Scotland they rose by 77%. Chiffchaffs increased by 133% across the UK and 244% in Scotland.
While the optimum breeding temperature for chiffchaffs is 13.5°C, willow warblers prefer a cooler 11°C. Over the last 30 years UK temperatures are 1°C warmer than the previous three decades.
Blaise Martay, BTO lead author on the research published in the journal IBIS, explains: “We’ve discovered that these two superficially similar warblers have quite different temperature requirements. Climate change means willow warblers are now faring worse in warmer parts of the country, something that has implications for future measures such as habitat creation.”
Here’s hoping we can change our ways for the better to give the willow warbler a helping hand.
Climate change means a mismatch of food needs and insects