After a gloomy, wet winter, the sun made an appearance this morning. This female blackbird did seem to enjoy it as much as me. Sat on a branch, she preened her feathers, fluffed them up and just took the sun in. Blackbirds can display a much more dramatic sunbathing behavior when on the ground. They will spread their tails and wings, fluff their feathers up, open their beaks and flatten their bodies against the ground. They appear to be entranced by the sun warmth, although to the casual observed they might look sick or injured. I have seen Starlings and House Sparrows 'copying' a blackbird doing this on a secluded corner in the local park, like the behaviour was contagious. Pigeons will regularly sunbathe as well.
Why do birds do it? Hypothesis abound, from synthesizing vitamin D from their oil gland secretions, to antiparasite behaviour. Sunbathing does not necessarily happen on cold or winter days (see example below). For a good article about sunbathing in birds see this post in TetZoo.
Today's blackbird doing some feather maintenance
Another female Blackbird sunbathing in the summer (26/06/2011)...
...and a male in the winter (03/02/2009)