Sunday, 30 November 2014

Ageing Great Grey Shrikes

Haven't done much today as we had a family shopping trip planned but an early morning visit to the moor, which was finally under blue skies, produced three skeins of Pink-footed Geese (totalling 300+) and Stonechat.
A chance meeting with John Bradley led to a discussion on the age of the Great Grey Shrike which he had just been watching by Wragg's Quarry,  whilst we were watching several Brambling on Bent Lane. John thought it was probably a first winter whilst I had indicated that I thought it was an adult based on the dark lores and the very narrow pale tips to the greater and primary coverts.
I've since checked various papers and photos and consulted George Briggs, who as a bird ringer has a lot of experience in ageing birds in the hand, and we now all agree that the bird is a first winter. George made the following comments;

"I think it is a this years bird due to several feather tracts showing a bit brownish, and also at least 2 greater coverts may by un-moulted."

Adult Great Grey Shrikes undergo a complete post-breeding moult and thus the majority of flight feathers and coverts are glossy black when they arrive in the UK in the autumn.
Whereas juveniles undergo only a partial moult of the body feathers and thus most of the coverts are worn and brownish black, with pale tips in the autumn.
Looking at photos of Great Greys in Britain the colour of the lores, the area between the eye and the bill is very variable and is often black in first winters.
Clearly the age of the bird is interesting as for a first winter bird this is its first visit to the area and it is not the same bird that has over-wintered in previous years.

Anyway it's a good excuse to post another photo.

Great Grey Shrike - first winter

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