Thursday, 13 August 2015

Willow Warbler recovery

I recently received the recovery report for the control Willow Warbler that I caught on Billinge Hill on 7th August and it had been ringed at Leighton Moss 29 days earlier. Not a particularly long or fast movement but interesting nevertheless. Willow Warblers migrate through the Billinge site in good numbers and 157 have been ringed so far this autumn. There has been a fairly constant turnover of birds since mid-July and this recovery is the first to indicate the origin of some of those birds.

Willow Warbler migration across the country is peaking just about now and this first year bird may have already moved on and reached the south coast or be even be further south in France. Not bad for a bird that may only be about ten weeks old, yes little more than ten weeks old and on its way to sub-Saharan Africa.

While on the subject of Willow Warblers the following image shows the tail of a young bird that must have had a severe fault bar that caused the tip of the tail to break off. The two complete tail feathers are replacement feathers and show how much of the other feathers has snapped off. Fault bars are caused by periods of poor nutrition when the feathers are growing and are testament to the grotty summer we have had.

IY Willow Warbler tail. The juvenile tail feathers have sheared off along the line of a fault bar. The 2 complete feathers are newer replacements and are easily recognised by being darker and more glossy.
Adult Willow Warblers have or are just about to complete their moult now and can often be recognised by having whiter bellies than first year birds. It is not a totally infallible criteria, as a few intermediates do occur, but is true in most cases. The condition and shape of the tail feathers is usually the clincher where there is any doubt.

Willow Warblers: First year left and freshly moulted adult right.

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