Wildlife enthusiast and resident volunteer at Exbury, Juliet, goes into detail about the Common house martin, who have a large colony in Exbury's water tower.
The water tower at Exbury plays host to a colony of Common house martins, where their nests are tucked up under the eaves at the top of the tower. The colony varies in size from year to year as populations are greatly affected by the weather.
The nests are made from mud, which the birds collect when they first arrive in spring, patching up old structures from the previous season, or starting again from scratch. Three of the four faces of the tower (south, east and west) are used, and the nests are built between the protruding roof beams. Each space can accommodate 2 nests, so a total of 44 on each face would be possible.
Over the past few years there have been about 16 occupied nests on each of the three faces of the tower; this year there are 46 in total with a further 6 occupied by House Sparrows. Most colonies consist of four to five nests, so Exbury’s colony is an important one. House Martins can raise up to 3 broods in a good year.
The best conditions for house martins require rain (for providing wet mud) and warmth, for good quantities of insects. While not much can be done about the weather conditions people can help martins (especially in a dry year) by providing a wet muddy area where they can collect material for their nests. Artificial boxes are also available and work best if you coat the entrance hole with mud. They are not long-lived birds, most breeding for only one season.
You can see the martins from quite a distance as they circle high around the tower, catching insects before swooping down into their nests. They are similar in appearance to swallows, but with shorter tails and gleaming white rumps. They will migrate south to Africa in September, though some stay around longer.