Naturalist

Birdsong - with a focus on warblers

The chiffchaff started calling in our garden on March 28th and a couple of days later one settled in the uppermost branches of a nearby hawthorn. Silhouetted against the sky we were able to watch the whole of its body pulsate with each pulse of its two-note serenade or in other words ‘singing its heart out’. Although we may tend to think of the romance of a cock bird attracting his mate with his song, remember there is also a lot of macho posturing, territorial disputes and naked aggression towards rivals! The demands of flight require a rigid fuselage for wings and their powerful muscles to operate so you may not know that the ribs of birds cannot move up and down to pump air in and out of the lungs as they do in mammals. (Anyone who has carved a chicken or turkey at the dinner table will have been cutting these muscles (breast meat) away from the breast bone of the rib cage.) Instead, birds have a series of air-sacs, like bellows that pump the air through the lungs, and the two largest are located under the wings so the movement of the wings also facilitates breathing and thereby song production too. Chiffchaffs are among the earliest singers from a large family of birds known as the warblers, small birds noted for the variety of their repertoire. The latest Collins guide lists 63 species, of which 14 breed in the UK and are the most likely to be encountered. They are all small birds (11-15 cm long) mainly feeding on insects, and with milder winters they may be extending their range from the European mainland. With a few notable exceptions most are either brown, yellow or green in colour and they are difficult to distinguish visually. As they frequent dense vegetation, with only fleeting excursions into the open, we have to rely on their songs for identification. Warblers are very good value in terms of decibels produced per gram of weight! The next warbler to listen out for will be the blackcap whose song is introduced by a series of churring notes preceding a remarkably musical warble. Cetti’s warbler, a relatively new arrival to this country, has an even louder version though I am not sure whether I am confident enough to identify its song. However the plaintive descending melody of the willow warbler is distinctive, as is the mid volume song of the whitethroat, a species that will sing from an open position. Both were relatively common but no longer appear in our garden. I must also mention the even smaller wren (not a warbler) which can still surprise me as it rattles off its rasping staccato from somewhere nearby. Astonishingly, if a recording of this is played at a slower speed (as is often done to make the ultrasonic calls of bats audible to our ears) it is heard to compose of a ‘whoop whoop whoop’ ululation reminiscent of gibbons in a tropical environment!