The distinctive song of the Willow Warbler (Latin name: Phylloscopus trochilus) has been heard on the reserve this week. This small summer visitor can be seen in woodland, parks and gardens across the UK between April and September, and has been heard singing by the visitor centre and the tarn at RSPB Geltsdale recently.
Willow Warblers are slim and delicate birds. They have grey-green backs and are pale underneath, with a yellow-tinged chest and throat and a narrow, pale stripe, called a supercilium, above their eyes. They have dark drown bills and eyes and pale brown or pink legs and feet. They look similar to a Chiffchaff, but with a very different song – warbling and melodic, as opposed to the Chiffchaff’s distinctive ‘chiffchaff, chiffchaff’ call. They are migratory birds, arriving in the UK in April and departing for southern Africa in September to spend the winter, so, unlike the Chiffchaff, you won’t hear them singing in the UK in autumn. They eat insects, spiders, fruit and berries, and can be seen hunting in leafless trees when they arrive here in spring.
Willow Warblers are widespread across the UK, but their success is mixed, as their numbers are declining in England and Wales, but increasing in Scotland and Northern Ireland. They are an Amber List species as a result. They are 10.5 to 11.5 cm long, with a wingspan of 16 to 22 cm - about the size of a Blue Tit – and weigh between seven and 12g. They moult all of their feathers twice a year – once at their breeding grounds in Europe and once at their wintering grounds in Africa.
When they breed, male Willow Warblers collect materials for a nest, which the females build on or near the ground, hidden in vegetation. The females then lay between four and eight smooth, white eggs with brown speckles, which they incubate for 12 to 14 days before they hatch. The chicks are then fed by the female and fledge 11 to 15 days after hatching, becoming independent 12 to 16 days after leaving the nest. Juvenile Willow Warblers have pale yellow superciliums and pale yellow upper bodies, with pale chins and breasts. Why not visit the reserve this week and see if you can spot these little olive-coloured birds and hear their distinctive, cascading song?