The voice of Rusty Blackbird isn’t particularly well known. Perhaps because the species is uncommon and its breeding grounds rather remote, it’s never been the subject of a formal bioacoustic study. But Rusty Blackbirds sing quite a bit — both males and females sing, in fact. They sing on the breeding grounds, on migration in fall and spring, and pretty much all winter long. The winter flocks I encountered in the swamps of Arkansas could be heard for half a mile.
Several authors have described Rusty Blackbirds as having two types of songs — one more creaking, one more gurgling — and this would make sense given that the closely related Brewer’s Blackbird has also been reported to have two different songs of more or less the same types. As I went through online recordings of Rusty Blackbirds, however, I came to the conclusion that I was hearing three different types of songs from the species, not two. Or is that two types of song and a very song-like call?
Three things Rusty Blackbirds say
The gurgle-creak seems like a good candidate for a typical “song.” It starts with a complex jumble of rapid notes and ends with a high monotone whistle with a metallic quality, like the creak of a rusty hinge:
Another song-like sound is the gurgle. It’s like the first part of the gurgle-creak, but at least twice as long.
Then there’s the creak. It’s like the gurgle-creak, but starts with only 1-2 quick notes, usually including a noisy “chuck” note much like the species’ contact call. On the spectrogram below, two creaks follow a gurgle-creak:
It’s fairly clear that these three song-like sounds are associated with different behaviors. The gurgle-creaks seem typical of songs — they’re practiced throughout the winter, getting gradually more stereotyped; they’re heard from spring migrants, who seem to have mastered them by the time they head north; and they’re delivered in long bouts on the breeding grounds, where they apparently function in territorial defense and mate attraction.
The gurgles, unlike the gurgle-creaks, are rarely heard on the breeding grounds. Instead, they mostly seem to be given by birds immediately prior to or during spring migration. The only recording I know of from the breeding grounds is from early in the season — 4 June in northwest Alaska. Perhaps they function primarily in pair establishment, and are used for just a few days after arrival on breeding territories.
Then there are the creaks, which seem to occupy an odd territory in between traditional “calls” and “songs.” Like traditional “songs,” they appear to be learned rather than innate — birds spend the winter practicing them, and the finished springtime performances vary greatly from one male to the next. Furthermore, they’re often deployed along with the gurgle-creaks by territorial birds on the breeding grounds, in response to playback of a rival’s song. That pretty well matches the classic definition of “song.”
But when else do we hear creaks? When Rusty Blackbirds mob Common Ravens. And in response to a tape of Northern Goshawk. And when a human threatens a nest. Most birds do not give songs, or anything like a song, in these situations. Instead we’d expect to hear alarm calls — typically harsh, noisy, simple sounds that carry far and don’t change from one bird to the next. Rusty Blackbirds have such calls — sharp chucks, long churrs, rattling chatters, and the like. As one would expect, they readily chuck and churr and chatter at ravens and goshawks and people, but they also give song-like creaks. What’s up with that?
Longtime readers of this blog will know that I don’t put much stock in the traditional “song/call” distinction, and here’s one more example of why not — a peculiar sound that straddles the traditional boundary in both form and function. Rusty Blackbird has attracted a fair amount of research attention in recent years due to evidence that its populations may be in steep decline. But I’m unaware that anyone has attempted to investigate its vocal communication. Here’s hoping someone will take it on — I think this bird deserves it.