Sunbathing birds

27.07.2002

Ó Robert Burton

The few hot days last week, which have constituted summer so far, resulted in an outbreak of sunbathing among the garden’s birds. In a spell of a few minutes I saw great tit (left), blackbird (right), song thrush and wren indulging.

I find this a strange form of behaviour. A bird is hopping about, then, quite suddenly, stops and goes into a sort of trance. It may pose with its body leaning away from the sun and the wing on the sunny side drooping, or squat and spread its wings and tail on the ground. The feathers of the breast, back and head are raised, presumably to let in the sun’s rays penetrate. Its beak opens to gives the bird a rather gormless look. The pigeons and doves have a variant in which they raise one wing, as they do when rain-bathing.

If this behaviour had a clear function I would expect it to be more widespread. The birds that were sunbathing in the garden were a fraction of the number that were present. But may be I am not observant enough. Ornithologists recognise two forms of sunbathing. Sun-basking is frequent, usually transitory and easily overlooked. It occurs at any time of day and serves to help the bird keep warm. In an earlier Nature Note, I described this behaviour among house martins. Sun-exposure takes place in the full heat of the sun, the bird is probably overheated and therefore pants to keep its temperature down. One likely function of sun-exposure is to render the feathers supple and straighten out any deformations. It has also been suggested that warming the feathers aids the spread of preen oil or stimulates the synthesis of vitamin D. This is conjecture. The birds may simply enjoy the sun’s warmth on their bodies, like we do.