Ten things you may not know about Willow Warblers
WILLOW Warblers are one of our most welcome summer visitors, with their bright plumage and delightful song. Although declining, especially in southern Britain, it is still easy to find and enjoy them in spring. Here are some interesting facts about Willow Warblers.
Willow Warbler is the most numerous warbler in Britain, with 2.3 million breeding pairs, raising up to 7-9 million young. It makes up about 16% of the birds migrating to Africa in autumn, with as many as 330 million birds.
Northern populations have a migratory divide in Sweden which separates two of the subspecies. The southern population trochilus migrates to West Africa, while the northern population acredula migrates to south-east Africa.
Birds have been tracked with geolocators from their breeding habitats in eastern Siberia. They fly to staging areas in south-west Asia and the eastern Mediterranean, before continuing to their winter destinations in Kenya and Tanzania. This is a distance of around at least 13,000 km, a record for a bird of 10 g or less.
Before migrating, Willow Warblers lay down fat quickly and before they migrate their digestive organs reduce in size to cut down body weight, and to provide both fuel and water.
Some Willow Warblers are monogamous and form single pairs with a mate, but there are males which will pair with two or even three females.
It is unusual among Phylloscopus warblers, having two complete moults of feathers every year. One takes place after breeding, finishing by about late August and the second takes place on the winter quarters from December to April.
It was once known locally in Britain as the Willow Wren. In Spanish it is the ‘mosquitero musical’ while in German it is the ‘fitis’.
Both male and female
Willow Warblers sing and some individuals occasionally include Common Chiffchaff-like phrases in their songs.
Its typical lifespan is two years, but the oldest British bird was 10 years 11 months 18 days. It was originally trapped in Wales in July 1999, and was recovered in Scotland almost 11 years later.
During the last 25 years Willow
Warbler has seen its breeding population decline by about 45%, with breeding success falling in southern England, possibly due to climate change.
Chris Harbard