Nuthatches look like small woodpeckers but, unlike them, can walk down trees head first, and instead of chiselling out grubs, they hunt for insects and split open nuts.
Although superficially similar to our wood-peckers in its choice of habitat and in its behaviour, the nuthatch is generally thought to be more closely related to the tits and tree-creepers. True, it climbs with great ease even on the trunk of the smoothest-barked beech tree, but the nuthatch’s toes are arranged three forward, one back, as in the other families of birds within the passerine order. Not two forward, two back as in the woodpeckers. It is also true that the nuthatch has a large, dagger-shaped beak just like a woodpecker’s, but this is the result of ‘parallel evolution’ (in other words it has evolved over the ages to do the same sort of work, but in a totally different bird), and the nuthatch lacks the extremely long tongue that the woodpeckers use to extract their insect food.
There are other, subtler differences. Woodpeckers always move head-up on a tree-trunk, leaning back on their stout tail feathers as if these were a shooting stick. But nuthatches can move with similar ease head-up, head-down, or horizontally across a trunk. Their tails are short, and the tail feathers are of normal shape, flexibility and toughness: only rarely do they come into contact with the bark at all, and nuthatches are able to rely on their strong claws alone to maintain their position on the trunk.
Nuthatches are attractive woodland birds, slightly more than sparrow-sized, neat but not gaudy. They are dove-grey above, white on the throat and the sides of the face, and a rich, cinnamon-tinged fawn on the belly. On each flank, and extending up under the wing, is a rich chestnut patch, considerably more extensive in area and darker in colour in the male than in the female, so with a little practice it is possible to separate the two sexes. The effective-looking beak leads to a striking long narrow black patch, running through the eye and backwards on to the nape.
This is rarely the case, for nuthatches are among the most sedentary of our birds, rarely moving more than a mile or two from the area of their birth. Their distribution is an interesting one: over an area roughly south of a line from the Wirral to the Wash they are widespread – except in a few lowland areas, principally in Cambridgeshire, which is probably because there are few suitable woodlands. North of this line they are much rarer, but are still spreading, and now breed in Scotland.
Their range seems to have contracted southwards, as the birds left their northern English haunts, during the 19th century, and at the same time it was noted that they had deserted the parks of central London and some other large urban areas. One suggestion is that this might have been due to increasing atmospheric pollution in industrial areas, reducing the insect food supply. This is borne out by the gaps in present-day distribution, with these gaps corresponding to the location of heavy industry and higher pollution levels, especially in northern England. Other species sensitive to industrial pollution – such as the kingfisher – are also missing from this area.
Though well-distributed in Wales, the nut-hatch is another of those birds (such as the tawny owl and the woodpeckers) whose complete absence from Ireland seems so puzzling. One possible explanation is that being sedentary birds, and having poor powers of long-distance flight, nuthatches were unable to reach Ireland during the re-colonization period that followed the last Ice Age. Before the rising seas formed what is now the Irish Sea and created an insuperable barrier.
Nuthatches are birds of mature, or even old, deciduous woodland; they sometimes occur in mixed deciduous and coniferous areas, but rarely in woodland that is predominantly coniferous. They particularly favour areas where beech, oak, sweet chestnut, hazel and hornbeam occur, for these provide winter food. Open parkland and, in many parts of England and Wales, large gardens with very old trees, also appear to be attractive to them.
Although the species is widespread within its area of distribution, the nuthatch is not a numerous bird in Britain. There are many sites that seem highly suitable, but where there are nuthatches at all. However, since 1974 the nuthatch has been steadily increasing in numbers and extending its range, with an estimated population today of about 50,000 pairs, which is still slowly increasing. This makes it commoner than the lesser spotted woodpecker, for example, but much less common than the coal tit.
The nest is built in a natural cavity, usually in a decaying broad-leaved tree but sometimes in a little-used or deserted building. Most are within a few metres of the ground, but nests at least 20m (60ft) high are on record. Nuthatches take readily to nestboxes, but other, more extraordinary sites include disused woodpecker and sand martin holes, an old magpie nest and even a series (reported from Sussex) in haystacks. Neither the size of the cavity nor that of the entrance hole seem to influence their choice, and nuthatches have a habit – unique among British birds – of cementing up the entrance with mud until the hole is of the right size. When using nestboxes, they also plaster round the lid, from the inside. Inside the cavity, the nest itself is also of a unique type. The eggs are laid on the floor of the cavity, on top of a layer of flakes of bark (especially of yew or larch if this is available), or of oak or other leaves. When the incubating bird (always the female) departs to feed or drink, she covers the eggs with similar debris, so on a superficial inspection the occupied nest looks like the long-deserted winter lodging of a field-mouse or dormouse.