Birding on the Net: Nesting Behaviour
While a pair are going about the initial stages of territory formation and defence, as well as courtship display, they have also been preparing to nest. One of the important aspects of most territories is that they should provide adequate shelter for the construction of that specialized form of shelter, the nest which must be able to protect the eggs and young from both the rigours of the climate and predators. Almost any position that affords protection and support can hold a nest, from holes in the ground to flimsy branches at the tops of trees. Most nests that are built above ground are found in suitable forks in trees and bushes. The larger nests are found on the thicker branches while some nests, like the Redpoll’s are found 12 metres up at the ends of branches, where they sway about violently in strong winds.
Some nests are open like those of the Woodpigeon and Turtle Dove, others are domed like those of the Magpie, Long-tailed Tit and Wren. Some birds nest on the ground or in holes. Puffins and Manx Shearwaters are even able to dig their own burrows in some loose types of soil. The Wheatear makes use of a variety of holes in the ground as well as in walls. Its preference, however, is for a burrow with a comparatively small entrance and an escape chamber behind the nest, into which the incubating female or mobile young can run if a predator comes down the burrow. Holes in trees are also regularly used, woodpeckers and Marsh Tits bore their own, but many other species including Starlings, tits and owls use old holes that have either rotted away or been excavated. Treecreepers quite often nest under bark which is peeling off. Kingfishers and Sand Martins excavate holes in sand banks close to water where they obtain their food supply. Along the sea-cliffs, especially where there are horizontal bedding planes, can be found colonies of seabirds. These bedding planes provide numerous ledges on which the auks and other species such as the Kittiwake nest. Because of the precariousness of the situation the young of these birds have developed special behaviour patterns to stop them from falling off.
Over the ages each species through the competition for suitable nest sites, has developed fairly specific types of nest so that an experienced person can identify a species simply by its nest and site.
The study of nests is fascinating, especially so after the eggs have been laid. However, one must remember that the nest holds very delicate objects. Searching for a nest may damage the eggs and young and could also sufficiently disturb the surrounding vegetation to induce the parents to desert or expose the nest to predators. Therefore searching for nests for its own sake should be discouraged. However, I am not suggesting the records should not be sought for the BTO nest record scheme. The BTO has its code of conduct for people taking part who realize that the scientific value of their investigation would be nullified by any disturbance of the birds.