Wednesday, 16 July 2014

Week 56: Willow Warbler ('Phylloscopus trochilus')

The Willow Warbler was @SpeciesofUK from 31st March to 6th April, 2014.

Willow Warblers are slim, delicate birds of woodland, scrub, parks and gardens.[1]

Willow Warbler
[Flickr Creative Commons © Muchaxo]

They migrate to the UK for the summer from southern Africa.[2] 

The willow warbler has recently been re-classed in a new family.

The willow warbler is one of the many birds that used to be grouped in the Sylviidae family, the so-called 'Old World warblers.’[3]

Sylviidae was used to describe small insectivorous birds of undistinguished appearance. But recently it's been split up into several distinct families.[4]

Willow Warbler
[Wikimedia Commons © Aviceda]

Since 2006, the willow warbler has been placed in the Phylloscopidae family with chiffchaffs, wood warblers and other so-called 'leaf warblers.'[5]

The willow warbler was sometimes known as the 'willow wren' up until the nineteenth century.[6]

Acrobatic Willow Warbler
[Flickr Creative Commons © Sergey Yeliseev]

The UK is at the edge of the willow warbler’s breeding range.

The breeding range of the willow warbler extends from the UK and Ireland at the very west, to Siberia in the east.[7] Willow warblers are the most common bird in Scandinavia, where they comfortably outnumber people.[8]

Willow warblers migrate to the UK and Europe for summer from southern Africa. The males arrive late in March and the females a couple of weeks after that.[9]

The willow warblers from eastern Siberia migrate about 12,000km to their wintering grounds in Africa, which is one of the longest migrations for a small bird.[10]

Juvenile willow warbler from Russia
[Flickr Creative Commons © Sergey Yeliseev]

The UK’s willow warbler population has undergone a moderate decline over the last 25 years, especially in southern Britain.[11] In Scotland however they’ve been very slightly on the increase.[12]

Willow warblers are small.

Willow warblers are grey-green on the back and pale underneath, tinged with yellow on the chest. They’re a small bird.[13]

Willow Warbler
[Flickr Creative Commons © Jose Sousa]

They have a pale supercillium (stripe above the eye).[14]

Willow Warbler Supercilium
[Flickr Creative Commons © gailhampshire]

Willow warblers are usually heard before they're seen. You'll notice a melodious, warbling song from amongst the tree canopy.[15]

Willow Warbler Singing
[Wikimedia Commons © Adreas Trepte]

Brighten your day with the willow warbler's lovely song: 

Like other warblers, willow warblers are insectivores, but will also eat berries and fruit in the autumn.[16]

Willow warblers are insectivores
[Flickr Creative Commons © Sergey Yeliseev]

Willow warblers are very similar looking to chiffchaffs.

However, willow warblers have pale reddish feet and chiffchaffs dark grey.[17]

A Chiffchaff
[Flickr Creative Commons © Brendan Ryan]

The best way to distinguish the willow warbler from the chiffchaff is by its song, which is very different from the chiffchaff's simple repetition of its own name.[18]

Willow warblers also tend to sing in the midst of smaller trees, whereas the chiffchaff prefers to sing in high treetops.[19]

Here is a short video guide from the BTO on the differences between willow warblers and chiffchaffs:

Strange but true…

Unusually, willow warblers moult twice each year - once at their breeding grounds and again at their wintering grounds. No one's quite sure why.[20]

[2] Derwent May, Nature Notes, p.56-57;
[9] Derwent May, Nature Notes, p.56-57;
[17] Derwent May, Nature Notes, p.56;
[18] Derwent May, Nature Notes, p.56-57.
[19] Derwent May, Nature Notes, p.57.

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