Tuesday, 7 December 2010

The Stonechat Complication

Last Sunday (28/11) I ringed a Stonechat at Tzor'a alfalfa field. In the net I saw wide paler upper-tail coverts and rump and I thought "what's that? Is it an Eastern or European Stonechat? No, it's a regular European Stonechat". After I ringed it, I looked again with more attention and I saw a regular Stonechat, slightly paler than European and with an off-white-buff upper-tail coverts and rump, typically for an eastern form. Another typical difference between eastern and European Stonechat is wing-length, the eastern is somewhat longer with 71-75 mm (n=3, Tzor'a Valley) and European 64-71 mm (n=63, Tzor'a Valley), it was 67 - good for European, too short for Eastern Stonechat.
Another typical difference is the colour of rectrices base in males. In European Stonechat (Saxicola torquata) it is a dark brown-grey, in Caucasian and Armenian Stonechat (Saxicola maurus variegate/armenica) it is clearly pure white, about quarter in Armenian and half in Caucasian. In Eastern Stonechat (Saxicola maurus maura) there is no white or only slightly at the base. But also in 'maura' Eastern Stonechat there could be white on base of rectrices, but under the upper-tail coverts, seen only in hand. This Stonechat shows clearly 10 mm white on base of its rectrices, but this is a problem because of our limited experience with that ID sign.

The Stonechat - first winter male, wing 67 mm

About 10 mm white on base of the rectrices

To copmare birds:

Caucasian Stonechat (Saxicola maurus variegate) first
winter male, wing 71 mm

European Stonechat (Saxicola torquata) first winter
male, wing 65 mm

Eastern Stonechat (Saxicola maurus) first winter female, wing 68.5 mm

Caucasian Stonechat (Saxicola maurus variegate) adult male, wing 75 mm

European Stonechat (Saxicola torquata) first winter male, wing 67 mm