Sir – Having studied the swifts in the tower of the University Museum, Oxford, for the last 47 years I have yet to see a swift perching.

Perhaps Peter Barrington, author of the article, (Threatened with swift decline, September 3) could explain to you how swifts can perch, they are not passerines.

They also stay in Oxford for four months not three.

Roy Overall, Oxford Museum of Natural History, Parks Road, Oxford