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.