The past couple of days, I’ve felt surrounded by chickadees. Little Carolina Chickadees are everywhere and they were very active when I went running this morning. Song after song after song. Now these cute, little birds are apparently the poor children in their genus (a taxonomic grouping). When I went looking around for chickadee papers, I found all sorts of things on related species- the Black-capped, the Mountain, the Mexican and even the Chestnut-backed Chickadees have all sorts of work done on them. Alas, the poor Carolina Chickadee gets (mostly) neglected. There’s certainly information out there, but not nearly the volume that shows up in the other groups.
One of the ways that much of the work on these little birds appears is in papers about range overlaps with the Black-capped Chickadees. Now these two species are quite challenging to differentiate. In the middle of the country where their ranges overlap, it can be very hard to tell which bird you’re looking at. There are, luckily, some vocal differences between these two species, though. One of the very cool things about their vocal differences, though, is not that they say different things, but that they say nearly the same thing in different ways. Both chickadees have a 4-note song in their repertoire- it’s usually written (for people- ‘cuz chickadees don’t write out their own songs) as ‘fee bee fee bay’. Both of these species use that same kind of song. Research on Black-capped Chickadees showed that individuals who were singing those 4 notes maintained a constant pitch ratio between the notes (so if they sang the first note high, the second note was always a fairly constant pitch beneath). If an individual changed the overall pitch of the song, the ratio still stayed the same. Black-capped Chickadees are said to rely on relative-pitch ratios in song production. Carolina Chickadees are a little more loosey-goosey with their song pitches. Well, in some ways. Their pitch ratios vary quite a bit. Unlike their relatives, however, the Carolina Chickadees tend to maintain a constant pitch with individual notes (a reliance on absolute pitch).
So why is this difference interesting? Well, to you, maybe it’s not. But if you were a chickadee, it’d be fascinating. If the Carolina Chickadee were a piano player, the first note of its song would always be right around middle C (though sometimes they’d be sharp or flat). A Black-capped, however, might start out at middle C or possibly an octave up or maybe at F. For the Black-capped, it’s not the starting point that matters, it’s how far down you go for the next note in the sequence (i.e. note 2 is two tones down from note 1- so if you start at middle C, then note 2 is an A; but if you start at an F, note 2 is a D). This whole thing also means that the important song features are different for the two species. We (as in we people) hear their songs as nearly identical and think, ‘ah, that’s a chickadee of some sort’, but the birds know what features in the song are important.
So, enjoy your absolute pitch Carolina Chickadees. Listen closely!