FYI, there was a multi-page treatment of the subject in ABA's
"Birding" magazine, which the magazine's Web site says was the
issue of Dec. '95, with a follow-up of some kind in June of '97.
I just saw the Dec. '95 issue lying around in my house
somewhere and I'll try to dig it up. But my memory of it is very
much what Hector describes, the primary conclusion being that
Hoaries are strikingly lighter colored and have a "pushed-in"
face with a noticeably tinier bill than commons.
Continuing to Google on the question, I ran into some criticism
of the '95 Birding piece on various birding listserves, but it's
still the most comprehensive and best illustrated discussion of
the subject accessible to the general public, as far as I'm aware
I remember the photos of the faces particularly convincing me
completely that I'd never seen a Hoary, despite having spent a
few hours here and there peering up at the underpants of various
likely suspects looking for streaking.
<Otherwise, I have *zero* personal expertise on this!>
hector galbraith wrote:
> First off, I, personally, am a wee bit skeptical about the specific
> status of hoary redpoll! Carduelis hornemanni has two races -
> C.h.hornemanni (the race that breeds in Greenland and that is seen as a
> vagrant in Europe [where it is called arctic redpoll]) is a beautiful
> little snowball of a bird and quite different from common redpoll. What
> we in the NE call hoary is usually the exilipes race. Exilipes is a
> different challenge, entirely. It is known that it interbreeds with
> common in the northern breeding areas and, in my experience, apparent
> intergrades appear in our area. I wonder if what we call hoary is
> actually just one end of the normal variation in common redpoll.
> Anyway, that aside, here are the field marks that I have culled from
> lots of different sources. In my opinion (and all of the below is simply
> that - not fact), three words of caution are important: (1) common and
> hoary redpolls present famously difficult ID problems and should be
> treated with caution; (2)given the high degree of variability in both
> "species" I think that it is probably not sufficient to just tick off
> one or two of the characters listed below and call it a hoary; (3)these
> characteristics probably apply most to adult males. Females and
> juveniles may overlap greatly with commons and intergrades and I am
> skeptical that they can be separated.
> Overall color - much frostier than male, female or juvenile commons. The
> ground color on which the streaking is superimposed is rather more
> frosty grey, than the more brownish grey of common.
> Rump color - a sizeable patch of unstreaked white, not grey, sometimes
> (often?) with a pinkish overtone.
> Flanks - unstreaked white or with fine pencil like streaking (unlike the
> heavy streaking of typical commons)
> Breast - white, sometimes (often?) with faint pinkish overtones (not
> like the reddish on commons)
> Head and bill - this, I think, may be the most important
> characteristics. The face of C.h. exilipes has a "pushed in" look. This
> is because the bill is much shorter and stubbier than commons and the
> culmen of the upper mandible is either straight or may even appear
> slightly concave.
> Overall shape - C.h. exilipes is often described as being "fluffier
> looking" than commons due to the fact that they, apparently, fluff out
> their body feathers more.
> Undertail coverts - either unstreaked or with limited streaking.
> This is as far as my knowledge goes. However, I have to come clean and
> admit that this knowledge has not been all that useful in the field!
> Over the last few winters I have looked closely at lots of redpolls and
> have not seen an undoubted hoary, though I've seen a few possibles. All
> of the above characters seem to vary more or less widely. The rump and
> undertail coverts are a case in point: I have seen lots of males that
> have virtually unstreaked coverts or that have unstreaked white rumps
> but that are otherwise typical commons. The head and bill shape (since
> it is structural) might not vary as much, but who knows. I am not saying
> that hoarys don't occur, or that they are not identifiable, only that
> because of my experiences I treat the ID with great caution.
> I guess that when faced with a likely candidate in the field my first
> criteria are head and bill shape and overall coloration. If the bird
> passes those tests, I would then go on to the other characteristics. If
> the bird passed all of these tests would I call it a hoary? Maybe, but
> I'd be more likely to err on the side of caution and call it hoary-type.
> Hope this helps!!!
> Hector Galbraith PhD
> Galbraith Environmental Sciences LLC
> 837 Camp Arden Rd., Dummerston, VT05301
> 802 258 4836 (phone)