Fresh from their migration after overwintering in Africa, house martins begin their UK residence on wetlands. There, they feed on aerial insects, before returning to their traditional nesting sites in May. These social birds are easily recognised by their distinctive white rump, forked tail and glossy blue-black upper parts. A breeding pair take approximately 10 days to construct their nest out of at least 1,000 beak-sized mud pellets, often in the eaves of houses. Colonial nesters, house martins usually gather in groups of four to five nests. The breeding season runs until August, taking advantage of high insect numbers.