Carolina or Black-capped Chickadee

I think Pittsburgh has both species of chickadees, and I can never tell them apart. I saw one this morning. Which chickadee is that?

Thanks,
Cui

Tentatively, Carolina, from the fairly plain wing (no pale secondary bar).

Hybrids are also possible in the overlap area . . .

Resin

Carolina Chickadee makes sense to me, based on the less contrasting wing color. Possibility of hybrids makes it more tricky. Since they can interbreed, why not just classify them as the same species? Are they really so different?

Thanks,
Cui

Getting into tricky species definition territory there! ;-)

The important thing is that the hybrids are less fit / less fertile than the parent birds, so they don't survive well. If the hybrids were as fit as the parent species, the two would merge and become indistinguishable in a surprisingly short time, within a hundred years or so. But the hybrid zone has remained stable, and narrow, since the two species were first discovered. All it has done is shift slightly northward as the climate warms. So they are maintaining their distinction.

Resin

That's good point. Interesting!

Thanks,
Cui

Got a new one today. Is that also more likely to be a Carolina Chickadee?

Thanks,
Cui