Another warbler. By now you can probably recognize them as such without even hearing them. They neither ascend nor descend.
Some are compact rectangles, like this one. The others have considerably more bandwidth per note than most other songbirds.
Today's species is one of the easier ones. Each individual bird has only one song-type. Syntactically the song is two-parted, meaning that one phrase-type is
repeated, followed by anothe phrase type that is also repeated. (This bird takes some liberties with that last rule, diminishing or even dropping the
second part in some of his songs.) Finally, the phrases are acoustically distinctive. The fine parallel lines that you see on the sonogram
translate to the "coarsely burry" quality of the sounds, in Pieplow's words. It is good that the songs are distinctive, because this species is
rarely seen well. They usually skulk in the luxuriant leafy underbrush of wet places. I was extremely lucky to encounter this bird at a time
when he was singing in full view, in a tree.
"Luxuriant leafy underbrush" could be described as the habitat of all four members of the recently enlarged genus Geothlypis. That genus
used to be the preserve of the Common Yellowthroat. It has been joined by the Kentucky, Mourning, and MacGillivray's Warblers, formerly of
Oporornis. It's a felicitous union. Kentucky Warbler, of the southeast, actually sounds a bit like the other two, except that it has only a one-part
song. Those two, which are sister species with complimentary ranges, sound very similar, although they can be distinguished in allopatry with
statistical analysis of recordings. But where their ranges meet in northeastern British Columbia, they hybridize and the songs are no longer
distinguishable. This is one of many hybrid zones in closely-related bird species.