Only Change Is Changeless, or: NAB v. 2017

The other day, on my way between errands, I stopped along a busy road where a midsize creek crosses beneath. There I saw an Eastern Phoebe alongside a Black Phoebe. Apparent hybrids have been documented in the area. A few days earlier, along another creek in my county, birders had reported a similar occurrence: a couple of Eastern Phoebes and a mostly or entirely Black Phoebe.

The ranges of Black and Eastern phoebes are rapidly expanding in my home state of Colorado, and known or suspected hybrids have been detected with some regularity. That’s cool. But let’s back up a step, or, to be more precise about it, let’s back up 10 years. A decade ago, Eastern Phoebe was casual at best in Boulder County, where I live—maybe three or four per decade, mainly in autumn. And Black Phoebe was rarer than rare—not even on the county list.

My errands concluded, I headed home. On pulling into the driveway, I heard a Say’s Phoebe. Black, Eastern, and Say’s, the phoebe trifecta: fun, but not really notable these days in Boulder County. I went down to the mailbox where the Bushtits are nesting. Then I went inside but not out of earshot of the ubiquitous Eurasian Collared-Doves. Bushtits and collared-doves: The latter were still semi-notable in the county 10 years ago, the former rare and unpredictable in the foothills to the west and unheard of around my neighborhood. So much has changed.

The phenomena I’ve just described—the Bushtit range expansion, the collared-dove blitzkrieg, and introgressing phoebes—are generally well known in the local birding community. Call it “received wisdom,” or simply “bird lore.” And that raises a question: Where does this knowledge about bird populations come from? From other birders, of course, but that begs the question.

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