Willow Warbler

The Willow Warbler is almost unique amongst birds in that it moults all of its feathers twice in a year.

Species introduction

At a glance
Latin name: 
Phylloscopus trochilus
Family: 
Old World Warblers
Family Latin name: 
SYLVIIDAE
Category: 
Birds

Species description

Species description

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.

Species photographs

Larger photograph(s) (click to magnify)
The Willow Warbler is almost unique amongst birds in that it moults all of its feathers twice in a year.
Willow Warblers are small birds with grey-green backs and pale under parts.

Details

Species family information

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.

Category information

The earliest feathered dinosaur fossils date from the early Cretaceous, but the ancestry of birds goes further back to Jurassic theropod dinosaurs, which shared a common ancestor with the crocodilians. Well known theropod groups include the tyrannosaurs, allosaurs, and other carnivores. Of surviving bird groups, the most ancient are the ratites (ostriches, rheas, tinamous, moas, kiwis, cassowaries, and emus), followed in evolutionary order by the waterfowl (ducks, geese and swans) and then the land fowl (chickens, turkeys, pheasants and their kin). Heene cemetery’s most ancient bird visitors are the woodpigeons. Strictly, therefore, we ought to refer to birds as dinosaurs, for they are direct descendants. The RSPB would be more accurately restyled as the RSPD. Where known, the conservation status of each bird is given as red, amber, or green, according to its survival potential based on 2016 populations and recent population trends.

Birds are warm-blooded, and have feathers, toothless, beaked jaws, and a strong, lightweight skeleton. They lay hard-shelled eggs. Their hearts have four chambers, and their metabolic rate is high. Although most are adapted for flight, many can also run, jump, swim and dive. Flightless birds retain vestigial wings. Brown, green, and grey are the commonest bird colours, for camouflage.

Protections

Legal protections and status
IUCN Birds of Conservation Concern: Amber List
Sussex Notable Bird List