Bird anatomy and feath­ers

How iden­ti­fy­ing bird feath­ers could help you spot a species you might have missed

Bird Watching (UK) - - Contents - WORDS: JAR­ROD COT­TER

ONE AU­TUMN MORN­ING, walk­ing through a nearby wood, I spot­ted an im­me­di­ately recog­nis­able feather. For more than 30 years I have honed my spe­cial­i­sa­tion in the ID of in­di­vid­ual feath­ers, and this was clearly a pri­mary wing feather from a Hawfinch, eas­ily iden­ti­fi­able by hav­ing a broad, flat-edged dis­tal por­tion (the fur­thest ex­trem­ity) which was a glossy black/pur­ple colour.

How­ever, de­spite hav­ing vis­ited this wood nu­mer­ous times, I’d never seen a Hawfinch there. The feather proved their pres­ence, so I planned more vis­its. As the leaves turned to red, or­ange and fi­nally yel­low, I scoured the lower ar­eas of the tree canopy on ever more fre­quent vis­its. I had no suc­cess for some weeks, un­til, one glo­ri­ously sunny day, I set my scope up on a tri­pod on the edge of the wood. Af­ter about 30 min­utes, I heard a scrap­ing noise above. Look­ing up, I saw a beau­ti­fully-lit Hawfinch scrap­ing the sides of his beak on a branch, to clean off the mess left be­hind af­ter a good feast. The point of this story is that without hav­ing found the moulted feather, I could have walked through that wood for years without ever know­ing Hawfinches were in res­i­dence. That said, the ID of a bird from an in­di­vid­ual feather is still per­haps the most poorly-de­vel­oped area of ap­plied or­nithol­ogy. This sit­u­a­tion has most likely arisen from the rel­a­tively few ex­perts in this field, and the con­se­quen­tial lack of a fully com­pre­hen­sive guide on the ID of in­di­vid­ual feath­ers. Yet, the sight of a freshly-moulted feather pro­vides firm ev­i­dence of a given bird in a given area, while the dis­cov­ery of a feather from a mi­gra­tory species can pro­vide valu­able data on bird move­ments. In the cases of rare and mi­gra­tory species, the bird may have made only a fleet­ing visit, un­known to the or­nithol­o­gist, but their feath­ers pro­vide a far length­ened pe­riod for dis­cov­ery and ID.

Plumage and feather de­vel­op­ment

A bird is cov­ered with var­i­ous types of feath­ers, known in their en­tirety as the plumage. The num­ber of feath­ers in a bird’s plumage varies de­pend­ing on the size of the species, from about 1,500 on a small passer­ine, to 25,000 on one of Bri­tain’s largest birds, the Mute Swan. The plumage per­forms nu­mer­ous func­tions, de­pend­ing on the type of feather. For ex­am­ple, birds are warm-blooded and so need to main­tain a con­stant body tem­per­a­ture. To achieve this, if a bird gets too hot in sum­mer, one method of keep­ing cool in­cludes fluff­ing up its feath­ers in a breeze to al­low cir­cu­lat­ing air to reach its warm skin, while to keep warm in win­ter the bird’s soft, downy area of feath­ers, close to its body, traps warm air against the skin. Feath­ers are made of ker­atin, a fi­brous pro­tein. Each feather has a fol­li­cle, a socket-like pit in the bird’s skin. In each fol­li­cle is a group of cells which pro­duce feath­ers, once a year,

1,500 ap­prox num­ber of feath­ers on a small passer­ine Feath­ers pro­vided a vi­tal clue to the pres­ence of Hawfinches é TELL-TALE SIGNS 25,000 ap­prox num­ber of feath­ers on a mute swan

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