A Song for July 29

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The dogs and I were still heading east, arriving as planned at Shamrock, Texas on the night of July 28. I picked up four "life birds" at Shamrock in 1969 on my first trans-continental drive, and the place has always felt special to me. It did not disappoint this time around. To begin with, there was the strong eastern flavor provided by Blue Jays, Carolina Wrens, and Northern Bobwhite. Shamrock is near the very western edge of the east. Add some spice with mid-continent specialties such as Golden-fronted Woodpeckers, Mississippi Kites, and Scissor-tailed Flycatchers. The latter were about 150 feet above me, on the top of a power pylon. Most of Pieplow's scissor-tail repertoire was filtering down from that height, reminding me that these gorgeous flycatchers are actually kingbirds.

The Scissor-tailed Flycatcher is now safely in the genus Tyrannus, where it belongs, but formerly it was classified in a separate genus, Muscivora, along with the Fork-tailed Flycatcher, which is now Tyrannus savanna. I'm sure that seemed reasonable to taxonomists who based their classifications on morphology, for those two species have extremely long, forked tails. At one time, it was standard to highlight extreme morphology, such as these tails, with generic status.

But the rise of molecular phylogenetics has shown that such features are often "phylogenetically uninformative." How can that be? Sexual selection can lead to extreme elaboration of traits if the the choosy sex, usually females, favors it. This can obscure the overall similarity of the sexually selected species to its close relatives that have not experienced rampant sexual selection. These tails are also aerodynamcially useful, and it may be that they evolved under natural selection. Regardless, scissor-tails sound a lot like Western Kingbirds. In fact, I called these birds Western Kingbirds until I got close enough to see them. W. John Smith recognized this vocal similarity in the 1960s and suggested including the Scissor-tailed Flycatcher in Tyrannus. It was done.

There hasn't been an update of Tyrannus phylogeny in a while, but now it appers that Scissor-tailed and Fork-tailed Flycatchers are not even closest relatives. In all likelihood, they evolved the long tails separately, instead of inheriting them from a common ancestor, vindicating the decision to include them in the genus with kingbirds. That doesn't mean the long tails aren't special; watch a scissor-tail catch a flying insect and you will agree.

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Email: web at archmcallum.com

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.