These pictures were taken recently by Dan Kingston at Waiparous Village, NW of Calgary. There are two leucistic chickadees coming to the feeders there. They have been seen together, and are likely litter mates. If you have an opinion as to which species they are, let us know in the comments. Also, the feet on one of the birds don’t look normal – any opinions on this?
I believe Terry is right – Boreal Chickadee. Of the three species we have here, this is the only one with buffy or brownish flanks. (Pacific Black-cappeds have buffy flanks but the ones we have here do not.) Also, although Black-capped and Mountain Chickadees do come to these feeders, the leucistic birds have been seen recently in company of normally-pigmented Boreal Chickadees.
Given the large amount of buff on the flanks, I would say Boreal Chickadee.