The sky is thick with housemartins and swallows today. Soon they will depart for warmer climes but today they are performing wild feats of acrobatics, swooping and diving outside my window. I don't think I have ever seen so many in one place. They congregate on the telephone wires in large numbers but over the last few years their numbers have been low. The experts suggested it was due to disease, many being killed off both here and in Africa (their winter destination). They must be back on form this year though.