The departure of our warblers in autumn is an exfiltration quite unlike the noisy invasion of their arrival in spring. The migration of the Phylloscopus, or leaf warblers, has begun and our observatory on the Kent coast has been catching and ringing large numbers of willow warblers and chiffchaffs on their way to their wintering grounds in west Africa and southern Europe.
Today, however, there was a rather more uncommon warbler in the mist net when we went to check. From a distance it had the fresh yellow jizz of a willow warbler, but my ringing companion, a retired vicar, drew my attention to its white belly. It was a wood warbler, first identified as a distinct species by the parson‑naturalist Gilbert White in the 18th century. He was the first person to discern, through careful observation of their song and behaviour, that the “willow wren” was in fact three distinct species: the willow warbler, the chiffchaff and the wood warbler.
White’s clerical successor carefully extracted our warbler from the mist net and placed it in a small cotton bag. A trainee ringer, an ecology student, was given the task of ringing the wood warbler. She used an AA ring – the smallest standard ring in use – and fitted it carefully it around the warbler’s right leg with a special pair of pliers. Then she measured the length of its wing, meticulously inspected its feathers and body to gauge its age and condition, then weighed it on a set of digital scales.
Our wood warbler weighed 9.9 grams – not a lot for a bird that will fly across the Sahara in a single flight, en route to its wintering grounds in the tropical forests of Liberia and Sierra Leone.
A ringer also has the privilege of releasing the bird they have ringed. All the trainees trooped outside to say goodbye. We knew it was this year’s brood and would be making its 6,000km journey on its own, with everything it needed to know about its route already genetically hardwired within it. She opened her hand and the wood warbler took off – all our slender knowledge about it contained on the tiny metal alloy ring around its leg.
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