A Song for August 02

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First, let's just appreciate these songs as what they are, beautiful bits of bird music. Two birds are singing above, one in the background. The sound at the bottom of the page is from another location, and so is almost certainly a third bird.

Second, let's discuss how they, the songs, make magic in our brains. I see three features worth discussing. The notes themselves are pure and ringing, like those of the Canyon Wren. Also, like the Canyon Wren's song, these songs descend in pitch. But, unlike that storied song, each note is not part of a gradual progression of change in pitch, duration, and shape. Instead, many of the notes are repeated once, producing a progression of doublets, as with the Indigo Bunting. So, the song of the Willow Warbler, one of Europe's most common birds, evokes for American ears two of the most-loved singers of North America.

Third, let's place this charming sound in phylogenetic context. The Willow Warbler is in the genus Phylloscopus. With around 80 species, it is one of the largest bird genera in the world, even though it uses only Eurasia (and a bit of Alaska in one instance) for the nesting season. Part of the large species-count comes from splitting polytypic species into several regional representatives of the same clade. (A polytypic species is one with enough geographic variation to have inspired the description of subspecies.) Even so, this group represents a profoundly successful "adaptive radiations." Species have to evolve different "adaptive strategies," reflected in different use of resources, to coexist in the same region. Swedish Lapland has four breeding species of Phylloscopus.

Despite those ecological differences, they have a single body plan, and most of them look devilishly similar. Luckily, their songs are often very different. The Willow Warbler's songs quickly rule out the Chiffchaff and the Wood Warbler, which look so much like the Willow Warbler. That being the case, I was relieved to finally hear this song after several days of seeing lots of Willow Warblers but hearing only call notes. The call notes are diagnostic, too, but there's a lot more to go on in a song. I'm still combing my recordings for any evidence of a Chiffchaff or Wood Warbler in the birchwoods of Nikkaluokta. For now, it's Willow Warblers all the way down.

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Nathan D. Pieplow. 2017. Peterson Field Guide to Bird Sounds of Eastern North America. Houghton Mifflin Harcourt.
Nathan D. Pieplow. 2019. Peterson Field Guide to Bird Sounds of Western North America. Houghton Mifflin Harcourt.
Donald Kroodsma. 2005. The Singing Life of Birds. Houghton Mifflin.