'Halo' effect question

I've recently been photographing seabirds and have noticed what I would term a 'halo' effect which is especialy noticeable on white feathers against a blue sky as seen below around the birds white breast. It also shows up but less noticeable with dark feathers. Does anyone have an explanation? Might the UV filter be at fault? Camera is a 400D and lens a 300mm f/4L with 1.4x TC.[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.23.16/Razorbill-4.jpg[/img]

OK, now I feel stupid! It's my monitor that is the problem, not my camera gear. Hope the pic looks OK to all of you.

Looks pretty good to me.


Nice shot.

looks good on my monitor.

Looks very good on my monitor (24" iMac)

Thanks everyone, think I'd better get my monitor checked out.