Bathing in the dust – and the sun – by garden birds is a bit of behaviour that often gets noticed at this time of the year. I’ve spotted little dents and divots on the dry ground and in my herbaceous borders. They’re the creation of the house sparrows that love rolling around. 

Why they do this isn’t entirely clear, but a couple of theories have been suggested. Just like our hair that gets greasy with the accumulation of oil from sebaceous glands in our skin, the same can happen in birds, as lipids and other oils produced by their preen glands accumulate on their feathers. It’s possible that a quick roll in the dust mops up this excess. It’s also been suggested that it helps abrade and scrub dead skin cells and dirt from feathers and skin. And maybe it can even smother or make life unpleasant for parasites that live in the feathers. 

Sunbathers are common too. Regular sun birds in my garden include robins and blackbirds, while the local house martins and dunnocks will often spread themselves out, with wing and tail feathers flattened against the substrate. They look like they’re enjoying themselves. But there could be another good reason for this. The warmth of the sun impinging on the feathers could help distribute those same fatty oils I mentioned. The heat makes them more spreadable, in the same way butter melts in a frying pan, with the warm lipids moving more easily across the surface of each individual feather’s features.