Wood warbler

The wood warbler (Phylloscopus sibilatrix) is, as its name suggests, a woodland bird. It winters in the forests of equatorial Africa and moves north to (mostly) northern Europe to breed. In Britain it is found mainly in the west with the highest density in Wales.

Appearance

The wood warbler is about 12 centimetres (4.5-5 inches) in length, making it slightly larger than the willow warbler. The upperparts are yellowy-green and the underparts are white, with the throat and breast being bright yellow. The flight feathers are brown with yellow edges. The head is the same colour as the back apart from a yellow stripe above the eye. The plumage becomes less highly coloured after the breeding season.

Female wood warblers are similar to males in appearance.

Habitat

When breeding, wood warblers prefer mature oak woods with limited undergrowth, but they are also found in woods of beech, alder, birch and pine.

Behaviour and feeding

Wood warblers feed mainly on insects such as beetles and crane flies, spiders and the caterpillars of moths. They eat very little plant material.

They will take insects on the wing or hover to take them from the undersides of leaves. They are very agile birds that hop rapidly along branches and, when displaying, flit from tree to tree in a flight that is reminiscent of that of a butterfly.

When perching, the wood warbler often lets its wings droop without the tail flick that is typical of other warbler species.

Outside the breeding season wood warblers are more difficult to spot as they are usually alone and seek cover in the upper branches of trees.

The wood warbler calls with a loud “pew-pew” and has a very pleasant song that accelerates into a rapid trill that has been likened to the sound of a coin being spun on a table top.

Breeding

Wood warblers return to their breeding grounds in late April or early May when the male birds will establish and defend their territories, often trying to attract two females at the same time.

Nest building is done by the female wood warbler, the nest being a fairly large structure with a side entrance, built in a tussock on the ground or underneath a fallen branch or trunk.

The clutch comprises five to seven eggs which are incubated by the female alone for up to 14 days. Both parents feed the chicks, which leave the nest at around 11 to 13 days, continuing to be fed for another few days. The family may stay together for up to four weeks, or it sometimes splits between the two parents.

A second brood may be raised, but a single brood is more common.

Wood warblers leave for their winter quarters between the end of August and the middle of September.

Conservation

Numbers of wood warblers observed in the United Kingdom have been dropping in recent years, with the most likely cause relating to the effects of climate change on their African winter quarters. Despite this trend, the wood warbler is sufficiently common throughout its range to be regarded as a species of “least concern” in conservation terms.

© John Welford