Saturday, 20 August 2011

True migration

Last Friday (19/08) I ringed at Tzor'a reservoir. This ringing session produced a great catch. Most noticeable was an early wave of Acrocephalus and Savi's Warblers, most adults, as expected from birds that perform complete moult in their African wintering grounds. Normally this wave passes through this area about week or more later.
The catch included 11 Common Kingfishers (all Juv.), 9 Great-reed Warblers, 6 Savi's Warblers, 1 Sedge Warbler (first this autumn), 1 Marsh Warbler, 4 Clamorous-reed Warblers and 17 Reed Warblers, total of 65 birds.

Marsh Warbler - juvenile

Notch on 2nd P = 8.0 mm

One juvenile Savi's Warbler showed an irregular moult strategy; this bird performed a complete moult, renewed most of the flight feathers and retained few primaries and secondaries; this strategy is called arrested moult. Another irregularity about this bird's moult pattern is the late stage of the moult; the innermost tails feathers and primaries are not full grown yet; Savi's Warblers only migrate through Tzor'a Valley (though they bred here till the 1980's) and most birds do not moult during active migration. So this bird is either an odd individual or perhaps hatched in the near area, maybe Hula Valley, either way it's very interesting.

Savi's Warbler - arrested moult