As of today I continue to see up to 2 dozen Common Redpolls (Carduelis flammea) and Pine Siskins, along with another dozen or so American Goldfinches. I'm going through 15 lbs. of thistle a week, and today they've emptied the feeders again. But among the numerous redpolls and siskins occupying the feeders I continue to see one, possibly two birds that may be Greater Redpolls (C. f. rostrata).
I first noticed a significantly large redpoll on the 12th of this month, when I came home from work. A single bird was on the feeder and appeared 'large'. With no other birds in the yard I considered it a bit unusual, since all of the finches/siskins/redpolls have travelled as a large flock, and this bird didn't spook when the rest of the flock did. On the 13th I found a large redpoll feeding among smaller redpolls at the feeders outside the kitchen window. The larger bird feed by itself at a feeder while the remaining birds fought over perches on the other feeders. I snapped a number of images of several birds so that I could compare sizes. The image shown left shows a composite of three that have been resized so that the feeders are all the same width (1.5"). The middle bird appears significantly larger and darker than the other two birds on either side. As they fed from the perches the middle bird also took an upright stance, while all other birds have an angled feeding posture. I'm guessing that possibly the larger redpoll has to squat more to reach the 1 3/8" tall feeder hole.
Both David Sibley and Ron Pittaway have written excellent blogs describing the rostrata Greater Redpoll. Generally these birds measure approximately 10% larger and 50% heavier, appear darker with more prominent streaking on the flanks. They have been observed in Michigan but not on a common basis. My bird(s) seem to fit this description. Note the heavy streaking on the sides of the larger, left bird in the first image at top (photographed this morning).
Since I haven't seen redpolls on a regular basis to know whether there is variability in size, I don't know if I'm seeing normal variations in my yard population. So I may not be seeing a real 'Greater' redpoll, but it sure gives me something to look for as I watch these birds empty my feeders.
I would love to hear any thoughts from you redpoll experts!