House Martins

In the Stone Age, before people arrived in Britain and started building houses, House Martins nested in natural cliff sites and there are still some cliff-nesting colonies in existence today. Once people started to build dwellings, House Martins gradually adapted to nesting under the eaves of houses (and under some bridges) where they are found today. They construct nests made purely of mud (at least 1000 beakfuls), some vegetable matter, and saliva and raise two, occasionally three, broods of 4-5 young. They will also use an artificial nest placed under the eaves. Their breeding behaviour is interesting in that young birds from an early brood will sometimes help the adults to feed the young of later broods. Young birds are frequently still being fed in the nest in mid-September and even into October.

House Martins migrate south in October to winter in Africa south of the Sahara (though their actual wintering area is unknown). They have not always been scarce; in the 1960s House Martins were considered to be more numerous than Swallows in some parts of Dartmoor. However, over the last 50 years numbers of House Martins have declined by around two-thirds and a national survey this year is attempting to estimate the current population. If you are lucky enough to have House Martins nesting on your house, please try to leave the nests in place for the following year; they often refurbish old nests when they return in spring. More information about House Martins, and about this year’s survey, can be found on the BTO website (www.bto.org).

In mid-April I was lucky enough to witness at first hand one of the natural wonders of the animal world – bird migration. I was staying on Lundy island in the Bristol Channel and observing the birds found on the island in spring. Whilst there, we had a migratory movement of many hundreds, probably thousands, of Blackcaps, Willow Warblers and Chiffchaffs. It is not unusual to see these birds singing and feeding in trees and bushes, but on this occasion they could be found in almost every habitat on the island. They were seen out in the middle of fields, in many of the rushy areas of the island and even out along the stone walls running across the island. It really brought home to me the urgency with which these tiny warblers – some weighing as little as 6 grams (a fifth of an ounce) – were heading north to their breeding grounds. A quick glance across an island hillside dotted with blackthorn bushes in full bloom revealed up to half-a-dozen warblers feeding in almost every bush. There were also many hundreds of Swallows, Sand Martins and House Martins, as well as other species, all hastening north. The migration was probably prompted by a change in the wind direction from northerly to southerly. No doubt linked to this movement, a number of migrant moths – such as Dark Sword-grass and Bordered Straw – were also recorded on the island.