How Birds Establish their Nest Site
Establishment of the nest site
Often it is the female of the species which selects the nest site and my observations of Goldfinches and Wheatears have shown that the female will start to take material to two or three possible sites before finally deciding on the one that will be used. In the Blackbird again it is the female which usually decides on the nest site. In hole-nesting species, such as the Common Redstart, the male sometimes selects suitable nest-sites before the female arrives. They walk over likely ground without actually forming any nest scrapes at first, then the male, sometimes with his mate, flies at intervals over his territory and from a height sings and displays with extraordinary passion and violence, after which he dives to the ground and either watches the female testing the ground for sites or occasionally leads her to others.
Some species, such as eagles, which spend the winter in their ‘home range’ may take several months deciding which site they are going to use. Others can make up their minds very quickly; when’the RSPB bought the Lodge at Sandy some of the staff visited it one day rather late in April and put up several nest boxes. Two hours later they decided to look at the boxes before returning to London and found that a Blue Tit had already started to nest.
Some birds return to the same nest site in succeeding years particularly if they are on fairly permanent structures. Oystercatchers on Skokholm used to return to the same scrape on a rocky outcrop. Eagles, Buzzards and Kites return to the same tree or cliff ledge, while Swallows return to the same mud cup. Some of the returning birds would appear to be the same individuals that have used the site in previous years, but, on the other hand, some sites would appear to be ‘traditional’, in that they have been used by succeeding generations of birds. Indeed, the Loch Garten Osprey site has been used for manyy years by a number of different individuals, although this would appear to be a special case as it is a protected site. Prior to 1954 the Osprey has been recorded as returning to sites which have been occupied on and off for many years. Birds of prey often have several choices of site which they might use in rotation.
A traditional nest site – one which is used on several occasions over a number of years by different pairs – presumably must have certain characteristics which suit the requirements of the species, making it an ‘ideal’ nest site or it may be that it is the only suitable site in the area. With larger birds, the choice of suitable nest sites is more limited and the building of a large nest takes some time and therefore it is advantageous for a pair to use an already established site. Evidence for the traditional use of nest sites in smaller birds is lacking, perhaps because the exact location of these small nests is difficult to describe. Wheatears on Skokholm tended to use burrows which had been used before by other pairs. W. B. Yapp tells of an ornithologist who visited some friends of his parents whom he had not visited for thirty years. He remarked that when he was a boy there always used to be a Goldcrest’s nest in a particular cedar. He then got up and went to the tree and put his hand under the bough and flushed a Goldcrest off its nest. In a large tree which changes shape or form slowly there is time for some small bird nest sites to become traditional. It only remains for the observer to know and record the nest sites of an area well enough and long enough for them to be recognizable in the future.