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13 July 2007
A male blackbird sits on my flower bed, spreading its wings and fanning its tail in the sun. Is it sick?
Sent in by Dennis Rimmell, Swanage, Dorset
Darren Oakley-Martin, Wildlife Adviser
Darren answers...
No, the blackbird is not sick, but you have observed some very interesting behaviour. It was indulging in behaviour known as sunning. This usually involves the bird adopting an unusual posture and deliberately positioning itself in sunlight. It may spread or raise its wings, fan its tail feathers, sit down, fluff the feathers on the head and back, and hold the head to one side, looking directly into the sun with one eye. In this country, sunning has been observed in blackbirds more often than any other species (Simmons, K.E.L. The Sunning Behaviour of Birds, Bristol Ornithologists Club, 1986).
No-one knows for certain the reasons birds do this and several theories have been proposed. However, sunning would appear to perform two separate functions: maintaining the bird's feathers in good condition, and helping to regulate it's temperature. There is even a suggestion that they do it simply because they enjoy it!
Precisely how sunning assists with the maintenance of feathers is not known, despite being widely studied. All birds have a gland on the rump, called an oil gland. The 'preen-oil' that this gland produces helps to keep the feathers flexible and hygienic. It has been suggested that the sun affects the preen-oil in the feathers in some beneficial manner, or that it helps to synthesize the Vitamin D from the preen-oil. This preen-oil also aids with waterproofing the birds' feathers. Additionally, the heat from the sun may stimulate activity in parasites within the feathers, making them more accessible when the bird starts to preen. Preening usually occurs directly after sunning.
Birds also make use of the sun's heat to increase their body temperature or prevent heat loss. This form of 'sunning' is also used when the bird dries itself after bathing. If however, the bird is sunning in order to maintain the condition of its feathers, rather than to raise temperature, there is a risk that it will reach critical levels. In this case, because birds cannot release heat by perspiration, it will have to regulate its temperature in some other way, so will gape and pant in order to lose heat. Whilst sunning, birds are often so absorbed in the activity that they are very approachable. This can make them susceptible to predators.
About Darren
I started working in Wildlife Enquiries at the RSPB in 2005. When I am not talking to people about birds at work, I spend much of my free time looking for them! I am passionate about birds and their conservation. I'm interested in how species have evolved and adapted, and fascinated by migration. For me, nothing beats standing on a beach in north Norfolk during autumn migration, watching thousands of terns and skuas pass by.
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