Greetings

A redpoll invasion seems afoot. For those interested in identifying Hoary
Redpolls, the best source is probably Dave Czaplak's article in Birding, vol
27, starting on p. 447.

The best ID marks are an unmarked rump (with the caveat that some Commons
have a small unmarked area on the rump) and unmarked undertail coverts. An
occasional Hoary has a long thin streak on the centralmost undertail covert
only. Such a bird seen out of range would need to be studied with exceptional
care to make a proper ID. The bill, though sometimes useful, can often be
difficult to assess. A slash of paler lower scaps contrasting with darker
upper scaps can be useful to ID as Hoary, if present.

Best Wishes
Steven Mlodinow