Saturday, 15 October 2011

Willow Warblers with unusual moult

Last days I ringed 7 Willow Warbler with suspended/arrested moult. Those were characterized by 2-4 unmoulted secondaries.  Normally, the adults of these perform a complete moult before autumn migration. The Willow Warbler is one of few species that complete two moult cycles every year. First I found birds with such irregular moult at the JBO (11/10) and I was very excited about this, but next morning (12/10) I caught another two individuals with such moult in Tzor'a Valley; both had unmoulted secondaries and a few lesser or median coverts; and on Wednesday morning another four birds. In his guide, Lars Svensson does not note this interrupted moult but I found this article discussing Willow Warbler's unusual moult from Sweden, describing a moult strategy similar to my birds. However, until today I have ringed several thousand Willow Warblers and have never seen this irregular moult before.

Two unmoulted secondaries

Unmoulted lesser and median coverts

Three unmoulted secondaries

In recent days I have ring many birds in Tzor'a Valley; three last ringing sessions produced 625 birds, most were Barn Swallows and Willow Warblers. Two new species for this season included Grey Wagtail and Wood Warbler; the juvenile Little Bittern and 2 Marsh Warblers were also nice.

Many swallows