Monday, 3 April 2006

Nuthatches construct a secure home

Over the last few weeks, a pair of nuthatches has taken ownership of the nestbox outside my office window. They must have found the box, situated high on the trunk of a beech tree, to their liking because this is the third year in succession that they have used it. Over recent days the male has been vocal in his proclamation of ownership. His song, made up of a series of piping notes, has been delivered from a high perch and periodically answered by another pair nesting nearby. The ringing call is a feature of early spring across much of southern Britain, where deciduous trees provide nesting and foraging opportunities. Later into the season the birds fall silent and attract less attention.

This particular nestbox is of a modern design, made from a mixture of concrete and sawdust (known as ‘woodcrete’), a combination that not only provides superb insulation but also offers protection from the unwelcome attentions of nest predators like grey squirrel and great spotted woodpecker. Seemingly not content with the nestbox as provided, the nuthatches have been busy gathering mud to cement the removable front panel to the rest of the box. This is common practice amongst box-nesting nuthatches, which will sometimes cement the box to the tree. Famously, one nest was found to have had nearly 4kg of mud added to it! Nuthatches often use mud on natural cavity sites, primarily to reduce the size of the entrance hole down to about 30mm, thus preventing access by larger species that might evict the occupants. The nest itself is a simple affair, the cavity lined by flakes of bark and dead leaves, within which the eggs can be hidden when no bird is on the nest.

Many readers will be familiar with this striking bird, with its seemingly overlarge head and long chisel-like bill. Blue-grey above, with a dark eye stripe, the underside is a mixture of buff and rusty brown. Perhaps the most obvious characteristic is the way that the nuthatch forages “head-down” on a tree trunk. Other tree-climbing birds work their way up the trunk, their bodies supported by strong feet and stiff tail feathers. While the nuthatch retains the strong feet, it has a soft tail, not used for support. Insects taken from cracks and crevices form the bulk of the summer diet, but during autumn and winter seeds are also taken. These may be inserted into a crevice and hammered open with the bill, to be eaten straight away or stored for another time. Judging by the continued use of the nestbox by my office, this particular pair has a territory with a good supply of both seeds and insects.

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