The house martins nest in colonies on cliffs or buildings, constructing feather- or grass-lined mud nests. The typical clutch is two or three white eggs; both parents build the nest, incubate the eggs and feed the chicks. These martins are aerial hunters of small insects such as flies and aphids. Despite their flying skills the "Delichon" martins are sometimes caught by fast-flying birds of prey. They may carry fleas or internal parasites. None of the species are considered threatened, although widespread reductions in common house martin numbers have been reported from central and northern Europe. This decline is due to factors including poor weather, poisoning by agricultural pesticides, lack of mud for nest building and competition with house sparrows for nest sites.