Quick! Male or female?
Got ya! For most of us bird lovers who aren't lucky enough to hold a Black-capped Chickadee in our hand, we can't tell a girl chickadee from a boy chickadee just by looking at them. Unless we see a chickadee as he sings the familiar "feebee" call (which only the male sings), we just live with it and accept it as one of the daily unknowns in bird watching.
But right now - during chickadee nesting time - we MAY be able to identify a male bird or a female bird. One way requires a close observation of a hard-to-see physical attribute and as a result, might be really hard to accomplish. The other just requires close observation of behavior, albeit during a very short time frame, and is something we all can do with a little time, knowledge, and practice.
First the hard one. During mating season, the male chickadee's external reproductive part - the cloaca - enlarges. Swelling at the base of the cloaca is most likely due to an accumulation of seminal fluid (as opposed to some other cause.)
Folks who band birds (and have the benefit of having the bird in their hand) will judge the degree of this enlargement on a 5 point scale. They may feel confident calling the bird a male with a 2 or higher rating.
Out in nature, if you're able to get a good view of a chickadee's underside, you may see the cloacal protuberance and, based on the degree of enlargement, be able to identify it as a male. There is a lot of judgement in this call, and doing it real-time versus looking at pictures may make it just about impossible.
Another visual that might be a clue is the presence of a brood patch, a spot on the female's lower belly area that lacks feathers, increasing the warmth that can be passed along to eggs during incubation. Since only the female chickadee incubates eggs, seeing a brood patch might help identify the female. This is not a large patch and it can sometimes be covered with surrounding feathers, so it too might be difficult to see.
Much easier is to watch the pair's behavior during the nesting season. During that time, certain roles are assumed only by the female. So if you observe two paired-up chickadees, you may be able to tell which one is the male and which is the female by their behaviors.
Here are the nesting behaviors that are unique to one or the other and which may give you a clear indication of sex:
- Only the female incubates the eggs.
- The male will call the female softly as he approaches the nest to feed her during the incubation period. The female may exit the nest to get the food from the male.
- Only the female broods the newly hatched young, again with the male bringing food to the nest.
You have a limited period of time to catch these behaviors. Incubation only lasts 12 days, and brooding of nestlings only lasts a few more days after that. One of the best ways to have a chance is to participate in the Cornell Lab's NestWatch citizen science program, as you will likely observe behavior differences between the adults during one or more of your nest checks.
I really don't know why I have this fascination with determining the sex of a chickadee. Maybe it's because it IS an unknown for most of the year, and unlocking the mystery is both a challenge and an adventure. It doesn't change a thing, but for some reason, I look forward to the challenge each year.
Sources: Julie Craves, Supervisor of Avian Research, Rouge River Bird Observatory and A Guide to Bird Behavior Vol. 1, Donald and Lillian Stokes