This winter is bringing most of the nation an influx of redpolls unlike any seen in decades. I was fortunate to experience a similar event during the winter of 1977-8 in the Chicago Area. During one day in early March, Ken Brock, myself, and 4 others worked a flock of 1000+ redpolls in a weedy field in nw. Indiana and found 5 Hoaries, one of which was the oversized and overly white Greenland race (not impossible, but highly unlikely to occur here).
As the number of redpolls have increased over the past month or so, a few reports of possible Hoary Redpolls have surfaced. I am not an expert or redpoll ID, though do have some experience with this lot and have recently discussed redpoll identification with friend whose winters are filled with redpolls (except for this winter, during which both species seem to have evacuated much of Alaska, and thus probably explaining in part our ample supply).
Clearly, in this forum, a treatise on redpoll ID is not possible, but as there seems to be some confusion as to ID, I figured I'd put in my two-cents worth.
Overall coloration, the appearance of of being whiter than other redpolls, should alert one to focus on a given bird. However, that overall coloration is the starting point, not the end. Of the many contributing marks, three should probably be given more attention than the rest:
1) rump streaking
2) undertail covert streaking
3) side streaking
As Bill Schmoker pointed out, Sibley's scoring system is rather useful. It can be found at http://www.sibleyguides.com/2008/01/a-character-index-for-redpoll-identification/
During the 1977-8 winter, I spent an entire day sniffing mothballs and looking at hundreds of redpoll specimens at the Field Museum of Natural History in Chicago. This probably explains certain aspects of my personality.
I do disagree with Sibley on a couple points, but first to the points we (mostly) agree upon: Rump streaking, undertail covert streaking, and side markings are the most important marks.
1- Undertail coverts. Any bird with one streak on the undertail covert has reasonable potential for being a Hoary, any bird without a streak on the undertail coverts is highly likely (but not certainly) a Hoary. There were no Hoary Redpolls in the Field Museum with more than three fine streaks on the undertail coverts, and there were only three examples of birds such as this. I would think any bird with more than one streak on the undertail coverts highly unlikely to be a Hoary, contra Sibley.
2- Rump. A bird with an large unstreaked rump patch is almost certainly a Hoary, and bird with an entirely, or almost entirely streaked rump patch is almost certainly a Common. Few birds fall in between
3- Side streaking. Here, I agree very closely with Sibley.
I've seen a number of redpolls that appear rather pallid, but are also heavily marked. I see no reason to think these birds are not Common Redpolls that have unusual wear, or perhaps, different diets. Therefore, I strongly disagree with Sibley's statement that: "Any redpoll paler than a typical Common should be assumed to be of tundra origin and one could make an argument for calling them all Hoary." I think David is not in the mainstream here. Again, pale overall coloration is a great way to figure out what birds to focus on, but once you do so, I think you'll find that many of those paler birds give no other reason to think of them as a Hoary.
The bill size and shape can be indicative. I've heard a variety of viewpoints on this from a variety of well-informed observers, and I'd say a really short and squat bill points heavily towards Hoary and a large and long bill to Common, but most birds fall in between, and apparent bill size and shape can change rapidly with angle of observation and how the bird arranges its facial feathers.
The red poll averages more limited in Hoaries, so something to pay attention to, but not definitive. Male Hoaries tend to be paler pink below. Again, average difference that changes as the months go by (birds get darker as winter progresses).
There are a number of other modest indicators, many discussed by Sibley, but I think this may help direct some. Sorry if I am being presumptuous in presenting this outline.
Happy Polling
Steven Mlodinow
Longmont
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