Saturday, 4 April 2015

Next Term, 7: Willow Warbler

One of the most delightful sounds of spring is the song of the Willow Warbler, which should be heard any time soon. I usually hear my first around the 6th of April, but the earliest I've heard one in these parts is on the 1st of April. I went to two suitable habitats on Thursday, and although there were several Chiffchaffs, there were no Willow Warblers.
Willow Warbler
Willow Warblers and Chiffchaffs because of their small size and their habit of picking insects from the underside of foliage are known as leaf warblers. The other UK leaf warbler, the Wood Warbler, is a bird that is only seen on migration in East Yorkshire, and then only in minuscule numbers. It is more than 20 years since I heard one at the back of the local cemetery, presumably on its way to the west or north. 
Immature Willow Warbler at Spurn
Willow Warblers are usually brighter than Chiffchaffs, but less so than the slightly larger Wood Warblers. However, one of Thursday's Chiffchaffs was fairly yellow, as was one a few years ago. Young Willow Warblers seen later in the year are even more brightly-coloured than the adults, which should be arriving next week. Both birds have a pale supercilium, but when in very close proximity you may notice a difference in leg colour. Those of a Willow Warbler are pinkish, or flesh-coloured, whereas Chiffchaffs have black legs. The Chiffchaff is also much more likely to continually dip its tail, especially in a figure-of-eight motion. If you look very carefully you may be able to tell that the Willow Warbler's wings look longer than a Chiffchaff's.  If you compare them look at how far the tip of the primary extends when it is at rest down the length of the tail.  The Chiffchaff only migrates to the southern Med or to North Africa, whilst the Willow Warbler migrates well south of the Sahara, and it needs longer wings for that more arduous journey.  However, the most reliable way of telling them apart is their song. The Chiffchaff has a cheerful, but very repetitive two-note song, whilst the Willow Warbler has a lovely descending, slightly wistful cadence.  
A very yellow Chiffchaff
Willow Warblers make a dome-shaped nest from grasses on the ground, hopefully protected by a bramble bush. They usually have one brood, but can sometimes manage a second, and each brood will probably be made up of between 5 and 7 eggs. In 2009 there were estimated to be 2.2 million pairs breeding in the UK. However, we have noticed in the last 5 years that numbers are declining in some of our best local woodlands.  
Wood Warbler
Although no Willow Warblers have returned yet, I remain confident that the will be back on habitat before the classes resume on 14th of April. I'm sure all the students will be enjoying the song and views of Willow Warblers during their first classes in less than a fortnight's time. 

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