House Martin

Mud nest construction

The house martin’s nest is a masterpiece of avian architecture — a domed cup of mud pellets with a small entrance hole near the top, plastered under the overhang of a roof eave, bridge, or cliff. The nest is built from hundreds of individual mud pellets, each gathered at the bill and carried to the nest. The whole structure takes 10–14 days to complete. The interior is lined with feathers and plant material. Nests are reused and repaired year after year; old nests may be used by house sparrows in the martin’s absence.

White rump identification

The house martin is easily confused with the swallow, but the white rump (visible in flight) is the instant identification feature. The underparts are entirely white (swallow has buff underparts and dark breast band), and the tail is short and forked rather than long and streamlined. House martins feed higher in the air than swallows, often in large swirling flocks high overhead.

Colonial nesters

House martins are colonial nesters — they prefer to nest in groups, often under the same eave or in adjacent positions under a row of houses. Colonies benefit from shared information about food sources: birds from a colony feed together, and successful foragers are followed by neighbours. The social stimulation of a colony may also promote earlier breeding.

Declining

House martin numbers have declined significantly in Britain since the 1970s — by around 50%. The causes are multiple and interconnected: loss of insect food due to agricultural intensification; loss of mud puddles from which nest material is gathered; house renovations that block traditional nest sites; and possible problems on migration or in African wintering areas.