Flat Rock Cedar Glades & Barrens SNARutherford County6/25/2015
Before anyone sees my title and freaks out, I did NOT see a Mexican Chickadee
in Tennessee!
However, I did see a very interesting Carolina Chickadee that I wanted to talk
about a little...
At the very back end of the blue loop trail at Flat Rock, I ran across a family
group of 3 Carolina Chickadees. Two of them were typical-looking, but the third
had a black bib that extended much farther down its chest (compared to the
other two) and dark gray underparts (unlike the typical pale creamy color of a
Carolina). It basically looked like a classic Mexican Chickadee.
Now, I'm confident it wasn't a Mexican because a) that would be essentially
impossible, since Mexican Chickadee is one of the most sedentary of all North
American passerines, and b) its call was textbook Carolina. But here's why I
find it interesting: Genetically, Mexican Chickadee is very similar to Carolina
and is generally considered to be its closest relative. (Carolina & Mexican
form a superspecies, as do Black-capped and Mountain. Black-capped and Carolina
are not each other's closest relatives, despite looking almost identical.)
So seeing this bird got me thinking... Carolina & Mexican chickadees presumably
arose from a common ancestor at some point in the past. So it's within the
realm of possibility that, given the right accumulation of mutations over
several generations, a chickadee that looks Mexican could arise from a
population of pure Carolinas. And that's probably what happened in this case.
Fascinating stuff! :-)
Daniel EstabrooksWinter Haven, FL
