Wet weather hard for Treecreeper

The almost mouse-like Treecreeper, with its delicate down-curved bill and mottled brown plumage, is most often seen working its way up the trunk of a tree, before flying to the base of a neighbouring trunk to begin the process over again. Although a relatively common breeding bird – there are estimated to be some two hundred thousand breeding pairs in Britain – it is easily overlooked. Unobtrusive in nature, and with a weak and high-pitched song, it is easy to see why it remains an unfamiliar bird to many observers.

Within Britain, the Treecreeper is primarily a bird of broad-leaved woodland but elsewhere in Europe it is replaced in this habitat by a close relative, the Short-toed Treecreeper. On the Continent our version, so to speak, is to be found in upland conifer forests and this may well explain why it managed to reach us at the end of the last ice age, while the Short-toed Treecreeper didn’t. The first trees to become established following the end of the ice age would have been coniferous and by the time that broadleaf trees became established, Britain had become separated from the rest of Europe. Now you might think that the English Channel is not sufficiently wide enough to prevent an avian colonist from reaching us. In most cases this is true, but Treecreepers are extremely sedentary birds and rarely move any real distance. A long-term study in a Nottinghamshire wood revealed that most birds move less than 500m once they find a territory in which to breed. Young birds may move several kilometres.

Being such a small bird and feeding on invertebrates, makes the Treecreeper susceptible to poor winter weather. At such times many different individuals may gather together within a suitable cavity or behind a flap of bark in order to share body warmth. This is a feature also shown by other small birds, such as Wrens. It is not just very low temperatures that can cause a problem but, in particular, the combination of low temperature and rain. This can result in a glazing frost which forms over the trunks of trees, preventing the Treecreeper from reaching its prey.

Treecreepers can be attracted to garden feeding stations, especially those gardens positioned close to woodland, by fat or suet that has been rubbed into the bark of a suitable tree. Make sure that you use a hard fat though, because soft fat can contaminate the feathers and reduce the insulative properties of the plumage. Specially designed Treecreeper nestboxes are marketed as another way of attracting the species into your garden. However, they are almost invariably ignored by Treecreepers (even in suitable woodland habitat) suggesting that the design is not quite right.