Willow Warbler photographed at Pleinmont [PLE] on 10/8/2013 Photo: © Rod Ferbrache (visit site)

The Willow Warbler is one of the commonest breeding birds in much of its breeding range which stretches from western Europe to the easternmost Siberia at central to northern latitudes (between the July 10C and 22C isotherms). In western Europe the southern most limit of its breeding range ranges eastwards from Bordeaux in southern France to Budapest and Odessa. It is completely migratory and winters in Africa, south of the Sahara. Birds from the western part of the range will pass through Spain and Portugal to winter in west Africa. Birds from more eastern parts of Europe (a migratory divides occurs in Sweden) will take the opposite route and migrate through countries such as Italy into eastern Africa.

Even though the Channel Islands are near the southern edge of its breeding range, it is perhaps surprising that Willow Warblers are not a common breeding species in the Bailiwick. Smith found them to be a 'tolerably numerous summer visitant' and records it as breeding in Guernsey. C.B. Carey found it to be commoner that the Chiffchaff and Dobson on 29 May 1946 found it to be more common, outnumbering Chiffchaffs, in the wooded cotils of the Kings Mills valley (presumably the Fauxquets and Talbot valleys which are now probably more wooded than at that time).

In Guernsey, a small number of birds breed each year, although the number of breeding birds is poorly known as no comprehensive surveys have been carried out but is currently probably in the region of <10 pairs. During the Guernsey Breeding Bird Survey, birds were recorded in eight of the twenty-three squares. These included several south coast valleys, Herm and inland wooded valleys. More recently birds have been recorded breeding (or in suitable habitat during June) in sites such as the Fauxquets Valley, Le Gouffre, Corbiere, Herm and other inland valleys. This species essentially prefers scrub and early successional stage woodland (5-10 years olds, pre-canopy closure), habitats which may well have been more common in Smith or Dobson's time.

Willow Warblers are a common, but rapidly declining, passage migrant and large falls of many hundreds or thousands of birds can occur in the islands in both spring and autumn. The first birds usually arrive back in the last week in March (average date is 27 March; the earliest date between 1969 and1998 is 11 March [UPDATE]) and birds are regularly seen throughout April and May, with occasional large (but unpredictable) falls. On passage, birds can be seen in virtually all terrestrial habitats and even on piles of vraic washed up on beaches! In autumn, the migration starts at the end of July and peaks in August. Occasionally very large falls of mostly juvenile birds can occur but these have become less frequent since the 1980s when this species started a a very rapid and large-scale decline from breeding areas in the south of the UK, where many of our migrants will come from. In the 1980s, it was not uncommon for 100+ birds to be caught per day by ringers operating in reedbeds in August but now 10+ is notable. The cause for the decline is unknown.

First thought to have bred in 1956 in CI or Bailiwick [CHECK]