Tuesday, May 29, 2007

I'll sing what I want to sing

So I was out in the far field yesterday, getting on for seven in the evening. I was tired from little sleep the night before, but wanted a quick amble around.

At the northwest corner I heard a song duel--very clear, very even, first one bird, then answered by the other, about 20 metres or less apart. I listened for a bit, I didn't know the song, but it was pretty ordinary, a mere trill, with a note or two at either end. But I didn't know it. Didn't sound like a warbler I knew, didn't have a sparrow quality to it. Should I track down one of the birds for a look, or let it go as one of the many mysteries of the field?

One bird was too close, sounded like I'd be able to get a look without much trouble, so I started to move over in its direction, slow, casual like, looking away as much as looking in the direction of the sound. And then it flew up to a bare branch and I got a very good look. I could hardly believe my eyes. It was a male golden-winged warbler, and it sang for me as I looked, so there was no doubt who was singing this song.

As I wrote recently, while reporting the return of the Brewster's Warbler to the far field, I haven't seen a golden-winged warbler back there since the summer of 2004, and so I was some pleased. But what the heck was that song? And who was the other duelling singer?

Caught up in the moment of discovery, I decide to see if I could track down the other bird. It was singing from a denser bit of foliage, fewer bare branches, fewer chances for a real look. I knew where it was, and saw it fly, but we moved around the field some, from tree to tree until finally it let me see it. A Brewster's.

The Brewster's warbler is a hybrid of the golden-winged and the blue-winged, too very closely related species, who are recently coming into contact as habitat changes and other factors are affecting the range of the blue-winged warbler. The blue-winged isn't as fussy as the golden-winged about habitat, and as a result of this (and, again, other factors) there is concern that the blue-winged will eventually swamp the golden-winged out. I've written about this a number of times, as I've watched it happen. But what I saw last night was a first for me.

The song was the song of the blue-winged warbler--at least pretty close to it. When I was collecting data for the Ontario Breeding Bird Atlas (due out in September 2007) I was instructed to only record blue-winged and golden-winged if I saw them, not to make a specific identification on the basis of song alone, because each will sometimes sing the song of the other. The golden-winged I got to know in the summer of 2004 sang a perfect golden-winged song, a nice series of 3 buzzes (the example I've linked is a 4-buzz song--just goes to show).

The Brewster's I've known since, including the one I reported earlier this year, have all sung the same perfect combo song. Of course, it might be the same bird I'm hearing each year.

The little scene yesterday between the male golden-winged and the male hybrid made one thing clear--these guys really don't distinguish (discriminate) between conspecifics and nearly conspecific. But it also raised an interesting question. Is it just a coincidence that these guys sang exactly the same song? Or, as seems more likely, were they singing the same song because they were singing at/for each other? Perhaps one started, then the other came by, heard the first, and matched him, to show he was the better bird.

In any case, now I'm hoping that there's a female golden-winged around who will take up with this male, and start a new, pure line alongside the Brewster's that I suspect have a territory already staked out further down the field. I will report developments.

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