The Western House Martin (Delichon urbicum) is a small swallow, glossy blue-black above and entirely white below, with an all-white rump that is the surest field mark against its relatives, including the Barn Swallow. It measures 13–15 cm with a wingspan of 26–29 cm and weighs just 15–23 grams, and shows a short, forked tail without streamers. In flight it gives a twittering "prirr" call, louder than that of the Barn Swallow.
A long-distance migrant, the House Martin arrives in Sweden in May and departs again in September, wintering in sub-Saharan Africa and tropical Asia, where flying insects remain plentiful. It feeds exclusively on flying insects, typically hunting higher above the ground than Barn Swallows. Its nest is a remarkable structure: an almost fully enclosed cup built from hundreds of small pellets of wet mud, plastered bit by bit under the eaves of a building and lined with grass and feathers, with only a small round entrance hole. Several nests are often built close together in loose colonies on the same wall, and a pair may raise two broods of 4–5 eggs each, incubated for 14–16 days. The species breeds across the whole of Sweden as far as Norrland, with a population estimated at 200,000–400,000 pairs, though numbers are declining — partly because smooth modern render and metal cladding give the mud nests poor grip, a problem sometimes eased by installing artificial nest cups under the eaves.
Read about this species in Swedish →