A Song for July 22

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Interstate 5 follows the path of least resistance as it connects Seattle, Portland, Sacramento, Los Angeles, and San Diego. But there are impediments, and Siskiyou Pass is the highest one. As you descend into California from its 5,000 foot summit, you come to the town of Yreka, and beyond it enter an incongruous intermountain valley that looks a little like Wyoming. It was there, on a country road just north of Weed, that I encountered these two nighthawks chasing each other over the prairie. They were mainly calling with peent, although I do hear a few distant fooms, their dive sound. I looked in vain for the dzik call, even though it's supposed to be used in chases.

Let's pause for a moment, and reflect on the evolution of nighthawks (Genus Chordeiles). They are nested, as a monophyletic clade, in a family of sit-and-wait, ground-based moth predators. Pre-adapted to an aerial foraging niche with an enormous mouth, the ancestral nighthawk (there are now six species) joined the swallows and swifts in the air. All three groups have big mouths and minimalist bills, all three catch and eat insects without using their feet, and all three are poets of flight. Yet all three have their own distinctive features. Like a practiced poet, evolution is constantly experimenting, often scrapping its experiments, constantly revising, as it cranks out poem after poem.

The chase scene was four minutes long, but I cut 100 seconds of it out. The nighthawks were off in the distance, and something else flew by, a single bird producing single loud calls (see below). I must not have looked up, because I called it a goose on the tape. It was not a goose. Looking at the sonogram, I thought it might be a Long-billed Curlew because the abrupt changes in pitch of the sound, seen in the sonogram, is characteristic of shorebirds. But the curlew's calls are more musical, less harsh. Paging through Pieplow's immeasurably useful guide, I found what I was looking for in the single-note calls of gulls. Remember, gulls and curlews are in the same order, Charadriiformes, so that style of pitch-change could be an ancient innovation of the entire order, a "symplesiomorphy." The two most likely gulls in Siskiyou County in July are Franklin's and California, and it sounds more like California to me. The spectral complexity before and after the break also aligns better with Pieplow's example. So, until further notice, it's a California Gull.

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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.