How to Know the Birds

• What: House Sparrow, Passer domesticus
• When: Friday, January 22, 2021
• Where: Lafayette, Boulder County, Colorado

Let’s see. We’ve still got nearly a week to go in this first month of the year. Thus far in 2021: a deadly insurrection at the U. S. Capitol, the second impeachment of then-President Donald Trump, the inauguration of President Joe Biden, and, tragically, close to 100,000 new coronavirus deaths in the country. Remember how 2020 was our annus horribilis? I recently heard someone quip that 2021 is saying to 2020, “Hold my beer.” If you haven’t had the time for a lot of birding this year, I don’t blame you. At the same time, if you’ve found solace in birds—even the most ordinary and workaday of birds—I’m right there with you.

The other day, jampacked at work as well as on the home front, I had occasion to step outside. Just to get the mail or something. Now I can’t tell you that I saw a falcon streaking past, or a solitaire perched atop the spruce across the street, or a band of bushtits making their neighborhood rounds. But I did hear this guy, proclaiming from a nearby residence:

Chirp! Chirp! Chirp! Chirp! Chirp!

It was a house sparrow, by golly, a male:

I have a question: Is this bird in breeding plumage yet? Well, that’s a trick question. House sparrows have only one plumage per year, which they get in the fall. As winter wears on, the male house sparrow’s feathers wear down—no surprise there. And as the feathers wear down, the bird paradoxically and surprisingly attains its breeding-season attire. Thus: The dull appearance in fall is created by fresh feathers, whereas the striking appearance in spring results from worn feathers.

It’s a clever strategy. No need to expend valuable energy on a metabolically costly spring molt, à la tanagers and loons and such. Just let ordinary feather wear do all the work for you! See how the black feathers on this bird’s breast are starting to appear? They’re not growing in, as you might expect. Rather, they’re starting to show as their dull edges and tips abrade. Love it! The male house sparrow’s breeding attire is already there, he just needs to let it all hang out by doing nothing.

House sparrows exhibit extreme sexual dimorphism. Case in point, this female—for all we know, the male’s mate—directly adjacent:

She had to have heard, just as I did, the male’s chirping. Or did she? What I mean is, Did she hear the male’s chirping the same way I did?

Recall how I rendered the male’s chirping:

Chirp! Chirp! Chirp! Chirp! Chirp!

The house sparrow sings “monotonous chirps,” according to the Nat Geo field guide. Sibley digs in on this point: “Song a monotonous series of nearly identical chirps.”

I don’t dispute that we humans hear house sparrows that way. But how does the female house sparrow hear the male’s song? Take a look at the sound spectrogram of the song:

The five chirps are impressively different.

In the same way that birds see electromagnetic radiation differently from how we do, so they hear sounds differently. I’m going to employ exceedingly casual language here, but, basically, house sparrows and some other birds hear sounds as if they were slowed down. Sorry to go all nerdy on you, but remember the scene in Star Trek IV where nobody can understand the sounds of the interstellar probe—until Spock and Kirk and Uhura ascertain that the probe needs to be listened to as it was intended to be? It turns out the probe was singing to humpback whales, not to human beings (and sundry other humanoid species from around the Alpha Quadrant).

Back to the house sparrow. The five songs, in addition to being obviously different from one another, are impressively complex. They comprise rising and falling traces, denoting what writers of field guides often describe as “caroling.” Think of a robin or grosbeak. Robins and grosbeaks carol slowly enough for our human ears to (sort of) hear it. But house sparrows evidently do not.

I’ve already confessed to casual language, and I now I’m going to engage in pure conjecture. I’m going to alter the house sparrow recording in such a manner that it might more closely approximate what the female hears. Scientists have done such work with other bird species, and it involves an approach to brain biology that I don’t even pretend to understand. But the most basic point stands: Female house sparrows somehow hear all those wonderfully varied squiggles.

With apologies to Comdr. Uhura, here’s a possible result:

Our house sparrow is become a robin! To be clear, this is exactly the same cut as above, just with a bit of tinkering: slower tempo, lower frequency, etc. And I went pretty light on the tweakage, actually. In case you were wondering:

I’ll say it again: This likely isn’t precisely what the female hears, but neither does she hear the song as a “monotonous series of nearly identical chirps.”

Something else before we wrap up. I mentioned in passing that house sparrows are sexually dimorphic. That is to say, they look different. Okay, but to whom? Nick Minor reported a while back in Birding magazine on immature male neotropical manakins that look like “boring” females to the undiscerning human eye; but they’re colored in the ultraviolet (UV) range of the electromagnetic spectrum inaccessible to our eyes. These “dull” birds are in fact blisteringly bright.

Could the female house sparrow, the drabbest of drab birds, be concealing a similarly marvelous secret? On the one hand, it seems likely, practically certain, that someone would have figured that out by now. Then again, we learned only in the past few months that the famous platypus lights up the UV. I’m not really expecting to read in Nick’s next Birding column that female house sparrows coruscate like platypuses. But I wouldn’t be hugely surprised to learn it either. Because here’s the deal: Every bird out there, practically every object and phenomenon in nature, is wondrous in ways we never imagined.

ooo

ooo