Cause of the effect

Could someone hazard a guess as to what caused the "ghosting" around the heads of the birds on this photo. It is the only one I took that day that exhibited this effect. No post except for the crop.

http://keiths.smugmug.​com …BBkz2/0/X3/IMG4​024-X3.jpg

Canon 7D
400mm (100-400L)
1/800
f/7.1
ISO 200

An alien duck maybe...
Nah,im joking. I have no clue. But,maybe lighting could be the issue here.

Kind of looks like chromatic aberration ... but maybe a bit too thick. Weird. Did you expose any shots correctly and that still showed up?

That was the only shot of about 40 with that effect.

There seems to be an inordinate amount of noise in the image for the ISO used.

If you run noise reduction on it the same issue is greatly exaggerated on the front ducks.

No idea what's causing it though.

If this is a 100% crop I'd think it might be a pixel-processing error in the software. Pretty strange though.

I've seen this when trying to do extreme local exposure adjustments, but as this is doesn't have any pp on it, I can't say.

Maybe you were moving the focus ring or something when the shot was being taken.

If not, it's probably an alien force field protecting the ducks.