Species: Willow Warbler (Phylloscopus trochilus)

Family: Old World Warblers (SYLVIIDAE)

Category: Birds

Location: SW

A. Birds

More extensive information on birds can be found in a separate blog post.

B. Old World Warblers (SYLVIIDAE)

The Phylloscopus, or leaf, warblers are amongst the smallest warblers and are to be seen flitting amongst the foliage, gleaning small insects with their delicate, pointed bills. Most are shades of green or yellow, and several species have prominent wing-bars or eye-stripes which play a major role in species identification (for the birds as well as humans!).
Most warblers in Europe and Asia are migratory, leaving their northern breeding grounds for the winter months to find insects in the warmer south. Most migration occurs at night, and birds will put on substantial fat reserves before undertaking these long journeys; it is not unknown for birds to double their body weight with fat in preparation. However, as climates change, this pattern of migration is evolving with birds not moving so far south, and a few individuals even overwintering on their breeding grounds.

C. Willow Warbler (Phylloscopus trochilus)

Willow Warblers are small birds with grey-green backs and pale under parts. They have a yellow tinged chest and throat and pale supercilium (the stripe above the eye). They are separated from the very similar chiffchaff by their song. Willow warblers have a yellowish or olive green breast with paler underparts. They have a brownish head with a pale yellow-green stripe above the eye, and flesh-coloured legs.

Long primary feathers on its brown wings give this bird a long-winged appearance, reflecting the huge distances it travels on migration. With a typical weight of around 9g, this is a dainty bird of a similar size to a blue tit. Its diet consists of a wide variety of small insects and spiders, and fruit and berries in autumn.

Their population, especially in southern Britain, has undergone a moderate decline over the past 25 years.

The Willow Warbler is listed on the IUCN Birds of Conservation Concern: Amber List. It is also on the Sussex Notable Bird List

Additional Information

Not to be confused with: the chiffchaff, which looks very similar but can be differentiated by its song and darker legs. Chiffchaffs make a ‘chiff-chaff’ sound while willow warblers have a lovely warble that descends in scale.


The Willow Warbler is almost unique amongst birds in that it moults all of its feathers twice in a year, on the breeding grounds and again on the wintering grounds; the reason for this is unclear but may have to do with the length of the migration (from Northern Europe to South Africa).