Photo: Keeping in touch: a treecreeper shrills out its contact call. They do this often, but it’s an easy sound to overlook
Few British birds can match the charm of the agile treecreeper, though you’ve got to spot this demure species first! What’s more, reports Bill Naylor, it has adapted happily to aviary life
THE Somerset name “tree mouse” aptly describes the movements and appearance of Certhia familiaris. Unlike a woodpecker’s “two toes forward, two toes to the rear” arrangement, the treecreeper has the standard passerine’s formation: three toes forward and one rear toe. However, its nails are long, especially the rear toenail. Its long tail, like a woodpecker’s, acts as a wedge, but also balances and supports the body as the bird digs for insects. Even during the annual moult, a treecreeper is never tail-less, as the tail feathers are shed in stages.
Treecreepers are industrious, foraging with jerky mouse-like movements. One will start at the foot of a tree and climb up the bark, often in a spiral, clinging upside down to branches with its sharp nails, and regularly poking its curved beak into crevices. The species favours aged or rotting trees, or ones clothed in ivy, where invertebrates are more plentiful. Even rustic gates, fences and walls are given a forensic once-over. Unlike squirrels or woodpeckers, which hide on the unseen side of a tree and peep out at the observer, treecreepers are too preoccupied to care if they are observed. If you stand perfectly still, they will venture surprisingly close.
The plumage is a blend of striated and mottled cream, gold and brown. Northern birds (of, for example, the nominate race C. f. familiaris, found in Scandinavia) have snowy white plumage on the underparts, flanks and throat. The broad white brush-stroke above each eye earned it another old country name: “ox-eye creeper”. (Ox-eye is more usually a name for the great tit.) The upper tail coverts are often tinged with orange, rather like tree lichen. A treecreeper’s cryptic coloration and long mousey brown tail camouflage it perfectly against tree bark. Though not uncommon, it’s more often heard than seen. The usual cheep-cheep call is used when it extracts an insect, or flies off in undulating fashion.
Worldwide there are nine species of treecreeper. The Eurasian treecreeper is well distributed throughout the UK and frequents deciduous as well as coniferous woodlands. On the Continent it is more usually confined to coniferous woodland, while the extremely similar short-toed treecreeper (C. brachydactyla) – a vagrant to the UK, which breeds in Jersey – takes over the niche in deciduous habitats.
Frank Meaden, aviculturist and British bird specialist, recorded the first UK breeding of the Eurasian treecreeper in 1968. An account of his success was published in the Avicultural Magazine Vol. 74. No. 6 (Nov-Dec 1968). Frank kept one male and two female treecreepers, five years old, in an aviary with adjoining indoor quarters. This was furnished with numerous vertical elm logs and slabs of rough bark to keep the birds occupied. Aviary mates included long-tailed tits and wrens, which often feed with treecreepers in the wild. Although, like many small arboreal birds, treecreepers bathe in wet foliage, in captivity they will also use a pond or receptacle, and bathe several times a day. They eat a large quantity and wide variety of invertebrates and their eggs and larvae. Tree seeds such as pine and spruce are also part of the diet, as well as seeds from flowers and plants such as knapweed.
Frank Meaden was unable to supply the variety and quantity of invertebrates that treecreepers obtain in the wild. However, he duplicated the high-protein nutrients by supplying a traditional old softbill mixture, consisting of minced steamed ox-heart and grated cheese, adding ants’ eggs liberally and mealworms sparingly. Baby powder and milk was also provided, as well as maggots and wax-moth larvae. Frank believed it was important to provide a variety of finely chopped green food every day.
Treecreepers roost in tree crevices and will use their beaks to enlarge these cavities to the size of a hen’s egg. Roost sites are usually on the opposite side of the tree to the prevailing wind. A sleeping bird assumes a position level with the bark of the tree, with body feathers fluffed up, head lowered and beak hidden. (Bird ringers are said to be able to dazzle a roosting bird with a torch, fit a ring, and replace the bird without it reacting.) The treecreeper’s favourite roosting tree is the introduced giant redwood, or sequoia, which first arrived in the UK in 1853. This tree produces soft, gnarled bark as it ages. Wherever these giants are found, treecreepers will use them for roosting. Like wrens and tits, in winter they will roost communally, in tree hollows.
During the breeding season, treecreepers can be fiercely aggressive, and groups of males have even been observed fighting on the ground like male house sparrows. Frank Meaden suspected his breeding treecreepers were responsible for the death of a wren and two long-tailed tits that shared their aviary. When pairs become interested in breeding, there are courtship flights and fluttering routines, in which pairs scuttle up and down tree trunks, calling sibilantly.
The warbling song goes see-see-sissy-see, and is rather like that of a willow warbler. Some writers say that it is only produced when breeding, but the great ornithologist T.A. Coward was certain he had heard it in every month of the year except September and October, when the treecreepers are probably moulting.
Breeding takes place in April or May. The nest site, which can be near the ground or up to 10ft (3m) high, is usually a tree hole, a crevice under the eves of a shed, or even a hole in a wall. A flap of ivy or loose bark often camouflages the entrance. Wedge-shaped nest-boxes have been found to be ideal for treecreepers and are commercially available. The nest may have a base of twigs. On this, grass rootlets and moss are added, and the nest cup is then lined with pine needles, wool and feathers. In April, one of Frank Meaden’s female treecreepers indicated that it was nesting when he spotted it carrying grass in its beak. The nest usually takes just over a week to construct.
The first clutch consists of five or six cream red-spotted eggs. In the South of England, especially, two clutches may be laid. The eggs are incubated for 13-17 days, mainly by the hen, with the male occasionally takes turns. The nestling period is about two weeks, but Frank Meaden’s young treecreepers left the nest far later, one at nine weeks and one at seven weeks. They are flushed from nest very easily. There have been a number of instances where vacating youngsters have landed on bird-ringers, apparently mistaking the vertical observers for trees!
Bill Naylor is the author of Misadventures of a Zookeeper, now available in digital format as well as in print.
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