A Song for July 08

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The Fox Sparrow's secret is pacing. The songs are far apart. The wait spawns anticipation, as with a meadowlark. The notes in the song are also unspooled at a deliberate pace, especially at the beginning of the song. You have time to savor each note as it rolls by. Every other bird in the vicinity is in a hurry; the Fox Sparrow seems to have all day to make music. Each male has several song-types, which he seems intent on never repeating in tandem. But neither does he have a rigid order of recitation. Here's how this bird deploys three song-types: A B C A C A B C A C. The last two songs are truncated, which is one of the ways birds with static repertoires create variety, or maybe the truncations were unintentional.

The Fox Sparrow is still regarded as a single species, despite decades of study of the rampant geographic variation it manifests. The Rocky Mountain birds, the "slate-colored" Fox Sparrows, range from Colorado up to the Cascade Crest, where they meet the "large-billed" birds from the Sierra Nevada and southwestern Oregon. The "sooty" group breeds from the Olympic Peninsula to Anchorage and beyond, while the "red" Fox Sparrows, which gave the species its name, are found all across the continent in the boreal forest. They are, or it is, the perfect example of the problem of species limits in taxonomy. If a species is defined as all the members of a lineage, no branch of which overlaps geographically with any other branch, then the Fox Sparrow is one species. The problem with that definition is that it would lump the Virginia's and Nashville Warblers into one species, or reduce our 11 species of Toxostoma thrashers to two or three. And this definition would play havoc with island endemics, which often diverge dramatically from the nearest relatives from which they evolved. If the Fox Sparrow were split into four, which would follow the recent trend set with other polytypic species, there would be many intermediate individuals from the contact zones that could not be assigned to one of the four species. This prospect has traditionally given taxonomists heartburn. They want "lineage sorting" to be complete before splitting a species in two.

As Van Remsen said, imposing a hierarchical naming system on a tree-like genealogical structure is bound to create problems. Ernst Mayr said taxonomy is an art. Phylogenetics is definitely a science; taxonomy, on the other hand, is a political activity. Taxonomy requires compromise, which is why it is decided by a committee.

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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.