There are a number of birds associated with houses such as swallows and swifts but perhaps the most outstanding one is the house martin. These small birds are back in the Highlands now and investigating their old nests from last year. As with many other migrants from cuckoo to swift and ospreys to willow warblers we tend to think that house martins also go to Africa for the winter months. However, with the house martin this is not straightforward as, intriguingly, we just do not known where they over-winter. This is all the more remarkable when you think that many thousands of these birds are ringed each year. The problem is that very few are ever seen in Africa and, again, nobody seems to know why.
One theory is that, rather like swifts, house martins do not come to land or perch outside the breeding season. This means that, incredibly, the birds must sleep on the wing in the same way as swifts. There is an indication of this as, whereas swallows and sand martins form huge roosts in places such as reed beds in the Autumn before their migration, the house martins never do this. So not only do they, supposedly, sleep on the wing in this country but also over areas such as the jungle when they reach Africa. If, of course, that is where they actually go for their winter. Of course, this is all very difficult to show one way or another. So the British Trust for Ornithology are now launching a fund to enable them to buy some tiny tracking devices to fit on individual house martins. These are tiny devices, no larger than a shirt button and when the birds are re-caught in this country the device is taken off. The analysis will show where the birds have been at any time or date. The devices have already been used successfully on nightingales and swifts as well as larger birds such as woodcock and other waders.
In the past, when there were far fewer houses, the house martins used to nest elsewhere. One main place was cliffs, many of them coastal although some were inland. Last year, for example, I found a few pairs building under an overhang on the sea cliffs at Tarbatness, on the east coast. Many years ago there was a colony of house martins on the inland cliff at Inchnadamph in Sutherland. It was part of what was then a National Nature Reserve. Since then the colonies on cliffs have become few and far between. Other structures, apart from houses, are used and one huge colony was at Aigas to the west of Inverness. There the birds built their nests on the side near the top of the huge dam. Last time I went to the site there were very few nests compared with what there used to be.
There are estimated to be between 38,000 and 74,000 pairs in Scotland. Even here, however, they have their problems. Despite the fact that it is illegal, some householders still knock down their nests as they are being formed. In contrast some people help the birds by erecting artificial nestboxes for them. These are successful and save the birds the time and energy to build their own when they arrive in the spring. One problem is that house sparrows will take over half formed nests of house martins although with the sparrows numbers falling this may solve itself. The photograph shows a house martin gathering mud for its nest.