Listening to a Continent Sing

Red crossbills! How I've been waiting for a close-up of them. I typically hear them flying by, their sharp kip kip calls high overhead, but never in my dreams had I imagined a flock landing on the ground in front of me, then flying up to a tree nearby where they'd call repeatedly before flying off into the distance.

But that's what happens here. At 0:05, they fly from the ground to the top of the nearby tree, where they've all settled in by 0:16; about ten seconds later they fly off into the distance, as all good crossbills seem eventually to do.

As I scan the sonagrams, I see that all of the calling birds seem to use essentially identical calls. That's expected, given that these crossbills belong to the goldfinch (Carduelinae) subfamily and the birds in that subfamily learn their calls from each other.

So just which "species" is this? I check the published catalogue of red crossbill flight calls in the Birds of North America and conclude that this is a "type 4" call. I don't know what that means, but some day someone will make sense of the wild variation and possible speciation that seems to have occurred among these birds.

Background

Wind and river, hermit thrush, ruby-crowned kinglet, dusky flycatcher.

Photo by John Van de Graaff