More thoughts on redpolls after yesterday's post, prompted by my own nagging doubts and a query from Nick Anich: In all of this redpoll ID discussion, I think people ask the general question "How can I identify a Hoary?" when what they mean is the more specific question "Just how pale/small-billed/unstreaked does a redpoll have to be before I can feel good about calling it a Hoary?"
I don't have the answer.
We know that there is a continuum of variation from the palest Hoary to the darkest Common, and that in the middle there are some (many?) intermediate (possibly hybrid) individuals that simply cannot be confidently assigned to either species. The questions are: Where is the middle, and how far from the middle does a bird have to be before it is outside of the range of intermediacy and therefore safely identifiable?
This mirrors the challenge of other similar species-pairs like Thayer's/Iceland Gulls or Western/Glaucous-winged Gulls. One can take a very conservative approach and identify only the extreme ends of the variation, or set the threshold at any point towards the middle.
The key phrase in the original question above, then, is what it will take before I can feel good about calling a Hoary Redpoll. Such subjective decisions require experience and careful consideration, and this is also to some extent a personal decision. Some people can tolerate a "probable" or "very likely" Hoary-type, others demand more certainty. It will also depend a lot on the context of the observation. In Barrow, Alaska, where Common Redpoll is a rarity, a lot of fairly dark birds are confidently labeled "Hoary". If those same birds were seen in the lower 48, where Hoary is a rarity, I'm guessing that they would be called Common. Observers in places where Hoary Redpoll is rarer will naturally set the bar higher for identification.
The birds in my photos are subtle, and I realize that if I had seen those birds in, say, California or North Carolina, I would be reluctant to accept them as Hoaries and would want a more thorough study of all features. In other words, I am not 100% confident that they are true Hoaries. But at that feeder, where I had seen one very pale and obvious Hoary, these few birds that were on the pale side and also somewhat fluffy and small-billed seemed like good candidates for Hoary and I was comfortable sticking that label on them. They are consistent with Hoary Redpoll, and match birds I have seen in northern Alaska. Whether they are pure Hoaries, or hybrids, or maybe even pale Commons, is an open question. I've revised yesterday's post to label them "Hoary-type" redpolls, which more accurately reflects how I think of them.
Having said all that, as I browse the photos of recent claimed Hoary Redpolls in the lower 48, they all look to me like solid Hoaries.
James Smith's photos from Gloucester, MA
James Smith's Redpoll pages from NH, winter 2003-04
Some recent photos from Michigan
I think people are being admirably conservative, and that such pale birds are well towards the pale side of redpoll variation and are safely identified as Hoary. It's understandable to wish for more certainty, but, if you can tolerate the uncertainty, I think there's a lot to be learned by looking for and studying the more subtle and intermediate birds.
Another excellent resource for redpoll info from Ron Pittaway is here