How did this happen, you ask. The presence of this bird was well known but it was only recognized as possibly a separate species—as opposed to a mere variety of its northern cousins—back in 1996. Field work has since shown...
…this new crossbill evolved because of a coevolutionary arms race between crossbills and lodgepole pine (Pinus contorta) in the last five to seven thousands years.
As South Hills crossbills exerted selection on lodgepole pine for increased seed defenses, lodgepole pine in turn exerted selection on crossbills for larger bills to deal with these increased seed defenses. This coevolution has caused these crossbills to diverge substantially in bill morphology from other crossbills. Because the South Hills crossbill is adapted to remove seeds from the well-defended cones there, it is a superior competitor and thereby limits the less well adapted and nomadic call types to breeding at very low frequencies in the South Hills.
And since the South Hills crossbills only mate (well 99% of the time) with other South Hills crossbills, we have a newly recognized species.
Congratualations to Julie Smith, now at Pacific Lutheran University, and her former graduate advisor, Craig Benkman at the University of Wyoming, for this discovery.
This is what a Red Crossbill looks like.
Of course for those really serious birders, the ones who keep life lists and never, ever throw away their notes after coming back from a walk, this will be one more they will have to search for. (Southern Idaho, heh? My son's out in that direction; might be time for a road trip.)
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