Thursday, 24 February 2011

White-winged crows

I managed a brisk walk around the Hermitage and Braids at lunchtime. Nothing beats patch birding really, even on days like today when the Dipper bombed off downstream as soon as I rounded the corner and the highlight was an all-too-brief view of a male Kestrel failing to catch a Chaffinch - maybe voles are proving scarce after the hard winter? As I passed a patch of scrub that I have checked repeatedly but unsuccessfully over the last few years for winter Redpolls and Bramblings, I grinned to myself, having seen both species already this morning from the comfort of my kitchen!

Once again, the area was finch-less, but never mind, on a patch there is always something of interest to watch.

Today it was a feeding flock of 70-80 Carrion Crows, which is a reasonably good size of flock for this species. These birds will probably be a loose association of birds without territories, and quite possibly would include a good proportion of 2nd calendar year birds.

Of these birds, I would estimate that somewhere between 5 and 10% showed clear signs of feather de-pigmentation (leucism) in their flight feathers. I am not sure whether this is a typical figure for this type of flock or whether the prevalence is higher at certain times of year or among birds of certain ages. Once I started looking it seemed that this flock contained an example of just about every pattern of feather de-pigmentation that I had seen in Carrion Crows before, from isolated asymmetrical patches, symetrical white flashes on parts of the wing, full broad white wing-bars through to almost fully white wings as in the bird shown above.


The next five pictures show five other birds from the same flock with different extents of de-pigmentation. Note that the bird shown above  also features in one of the the photos below, and the photo to the right also shows a more normally plumaged bird.








Finally, here is another Carrion Crow from the same flock. Most of the de-pigmentation on this bird is not visible when the bird is feeding.



4 comments:

welchs said...

Nice pics, 5-10% does not seem unreasonable to me, sure it would be around that figure here in Longniddry too though sometimes boosted by several siblings showing same.

Not directly related, but have you seen this little beauty: http://www.flickr.com/photos/tonybrierton/5468795111/in/photostream/ - erythristic?cor

Morg said...

Not sure that link quite works - maybe this one? http://www.flickr.com/photos/tonybrierton/5468795111/ - a jackdaw with pale brown wings... I'd like to see that - seen a few odd bits of plumage in the Jackdaws around here, but nothing as extensive as that.

Cheers,

Geoff

welchs said...

Yes, that's the one! There was the stunning mottled Jackdaw from Linlithgow a couple of years back, you can see in Kris's LBN photos here: http://groups.yahoo.com/group/lothianbirdnews/photos/album/111462325/pic/list

I once had a less extreme case here in Longniddry.

Morg said...

Impressive bird - I have not seen anything like that - but I'll be keeping my eyes peeled.