House martins

Returned from migration to Rannoch - 14th April 2020.

House martin

(Delichon urbicum)

Photo Creative Commons - credit Loobie 1805

House martins are summer migrants from Africa. There are over 500,000 pairs that breed in Britain although that is only a third of the number that there used to be. They are more inclined to nest in cities than swallows but in the mid-20th century they disappeared from Central London because of air pollution. They have returned although there is still some way to go in eliminating air pollution in London.

In Rannoch the Loch Rannoch Hotel is much favoured by nesting House Martins.

They are one of the four similar British swallow-like birds that catch insects on the wing. These are - Swallow, Swift, Sand martin and House martin.

The house martins has a white rump and that is the easiest way to distinguish it from the swallow. Sand martins are smaller and largely brown whilst swifts are larger and have very swept back wings.

Photo Creative Commons - credit Ómar Runólfsson

House martins make neat nests out mud stuck under the eaves of buildings. It take them about ten days to make the nest and the female does most of the incubation. Sometimes the house martins nest in very large colonies and their nests may be close enough to touch. There is a certain amount of conflict with house sparrows which sometimes evict the house martins and take over their nests.

House martins are preyed upon by Hobbies which are small and very agile falcons.

One of the mysteries of bird migration is where do house martins go in winter. It is known that they go to sub-Saharan Africa but where exactly and how they get there is not known. They are seldom seen in Africa, perhaps because they go to the rainforests of West Africa and spend much time high in the air. A few European birds overwinter Spain and Potugal.

The British Trust for Ornithology is embarking on a research project to try to find out where they go in winter. They will be attaching geolocators to about twenty birds. The geolocator is a shirt button sized device that records light, has a clock and a calendar and weighs less than a gram. It has enough memory to retain this information for the whole period of the migration. Scientists can then work out the position of the bird on the Earth’s surface from the day length, the calendar date and the time recorded. The same geolocator device has been used previously for cuckoos.

In general house martins arrive in Britain in April and leave in September.