Polymorphic Polyandrous Perplexity (by Joe Eaton)


We’ve been spending a lot of time in the company of Swainson’s hawks lately, at an undisclosed location in San Joaquin County. They seem to be everywhere, even in semi-suburban areas. It’s been an education. I didn’t know Swainson’s hawks hovered; they’re quite good at it, even in a stiff wind. I’d never heard their scream, much like a redtail’s but somewhat thinner and more wavering. And I’d never seen a pair mating or building a nest. All this has been happening just around the corner, within an easy walk of where we’re visiting.

Swainson’s hawks, like many other buteos (including red-tailed, rough-legged, ferruginous, broad-winged, and short-tailed hawks), come in multiple plumage morphs. “Morph” is the preferred term, not “phase,” because it’s permanent.The extremes are the light morph (brown bib, white belly) and the dark morph (all dark below), with rufous and intermediate variants. Proportions of different morphs in a population vary geographically, with dark birds predominant in the Central Valley and light birds on the Great Plains. Mixed pairs are not unusual.

We were out for a constitutional last month and watched three Swainson’s hawks—two dark, one light—interacting in what you could probably call a walnut savanna. The two dark birds were acting like a pair, calling back and forth, eventually touching down on a gnarly old walnut and mating. So I thought I had this relationship figured out: the dark hawks are on territory, the light bird is an interloper. But then we saw the larger dark hawk, the presumed female (female buteos being larger than males in most species) flying in tandem with the smaller light hawk and briefly locking talons with him. Sure looked like courtship.

I consulted the trusty Cornell Birds of North America site, which is really worth the cost of the annual subscription, and found a reference to Swainson’s hawks in northeastern California forming stable polyandrous trios. A female and two (related? unclear) males defend a territory, build a nest, and jointly care for the young, sometimes for several years in succession. Was this what I was watching? The following morning, though, I caught the two dark hawks carrying sticks into an isolated live oak, where they had already constructed a sizable nest, deep and bulky, near the crown. No sign of the light male; might have just been passing through, looking for an extra-pair copulation. As it turns out, that was the last time we saw him.

Polyandry, it seems, is not that unusual in buteos and related hawks. It’s more or less standard for the Galapagos hawk, which genetic studies indicate is the Swainson’s closest relative. (The i’o or Hawai’ian hawk is also near kin. Swainson’s is typically a long-distance migrant, with most of the population traveling from the North American plains to the Argentine pampas every year. You can see how accidental colonization of remote islands might happen.) Polyandrous mating groups also occur in the more distantly related Harris’s hawk. The advantage? Male raptors often provide prey for their incubating mates and nestlings. A female with two male providers would have a better chance of successfully fledging her brood.

Central Valley Swainson’s hawks migrate, but not to Argentina. Migrants travel only as far as western Mexico and Central America; a few spend the winter in the Valley or Delta. This, along with the different morph proportions, led to speculation that they might be genetically distinct from the Great Plains population. And they are, kind of, according to recently published research by Joshua Hull and colleagues at UC Davis–but not genetically different enough to meet the criteria for federal protection as a Distinct Population Segment. There’s apparently enough gene flow between Valley and Great Basin hawks to keep the populations from diverging too far. That’s too bad, given the Valley hawks’ widespread loss of habitat and precipitous (90 percent in the last century) decline in numbers.

Look Me in the Pistil


It’s been a scarily dry/snow-deficient year in the Sierra Nevada. Nevertheless, there are some brave souls showing up in Calaveras Big Trees State Park. Here’s one: Fivespot, Nemophilia maculata.

(I might be a bit behind the curve on its specific epithet, but that’s another rant.)

The Fossils Say “What?” (A certified Joe Eaton Rant)

This is what gives science journalism a bad name:


I’m assuming that Douglas Martin, assigned by the New York Times to write the obituary of paleontologist Farish Jenkins, has some kind of science background. Maybe not. Maybe he’s an obit generalist—I believe the Times has such people. Maybe they pulled him off the sports desk. But you’d expect the Newspaper of Record to at least have someone knowledgeable—Carl Zimmer? Sean Carroll?– review the piece. This, clearly, was not done.

True, you can’t blame Martin for the headline: “Farish Jenkins, Expert on Evolving Fossils, Dies at 72.” Fossils as such do not evolve. They’re dead bits of shell and bone, often with the original content replaced by minerals, sometimes just impressions of the hard parts. They’re a rich source of data for students of evolution. But it was the living organisms that evolved, not the fossils. Let’s give that a pass, though, and move on.

To the first graf, in which Martin blows it completely: “Farish Jenkins, a paleontologist who discovered fossils of animals evolving into something new—most notably a 375-million-year-old fossilized fish with skull, neck, ribs and a part of the fins that resembled the earliest mammals—died on Nov. 11 in Boston.” Fish parts that resembled those of the earliest mammals? More like the earliest tetrapods, four-limbed creatures that we might as well call amphibians for the sake of convenience. Mammals are only one kind of tetrapod, along with amphibians, reptiles, and birds.

What Martin seems to have done is to conflate Jenkins’ role in the discovery of Tiktaalik
rosae, a fossil fish with many tetrapod-like anatomical characters—a neck, for one—with his unrelated work on the evolution of the mammalian inner ear from a portion of ancestral reptile jawbones. Martin, oddly, never mentions Tiktaalik by name. Its story is fascinating, and well told by Jenkins’ colleague Neil Shubin in Your Inner Fish, who does get a quote about Jenkins. The gist: there’s a long evolutionary lineage from Tiktaalik and its contemparies to their reptilian descendants to the first creatures that can be considered remotely mammalian, and their jawbones went through a lot of changes before they became our malleus, incus, and stapes.

Martin winds up with this: “In 2010, scientists found fossil footprints in a quarry in Poland 25 million years older than Dr. Jenkins’ find [Tiktaallik]. Creationists said these proved that the ancient fish Dr. Jenkins had found could not have been a missing link, since creatures into which they supposedly evolved were already long extant.” Come on, Times! “Missing link!?” Tiktaalik wasn’t missing. It was there in the rocks of Ellesmere Island all the time. As for linkage, it may have been a step between fish and tetrapods; it may have been an evolutionary dead end. But it does embody a stage through which the common ancestors of frogs, alligators, hummingbirds, and humans must have gone. Somewhere in our past, there was something a lot like Tiktaalik. Martin also misses the chance to refute one of the stupider creationist arguments, a variant of “If people evolved from apes, why are there still apes?” Old lineages don’t always die out when they bud off new ones. Apes aside, horseshoe crabs and lungfish are still with us.

If the Times, which presumably has an elite readership, is capable of this kind of crap, no wonder more Americans believe in angels than in evolution.

Like Other Left-leaning Dissenters of His Time

(Another one from Joe)

Barry Commoner, scientist/activist, died a few days ago. I never met him, although I heard him speak in Sproul Plaza during his 1980 presidential campaign as nominee of the Green Party, which could almost be taken seriously back then. I may even have voted for him. That election (Carter versus Reagan, for those who came in late) was almost as dispiriting as this year’s. I also read his books, which were lucid and, in a cautious way, encouraging. Commoner was a geek, but he also seemed to be a mensch.

This is how the New York Times noted his passing: “Like some other left-leaning dissenters of his time, he believed that environmental pollution, war, and racial and sexual inequality needed to be addressed as related issues of a central problem.” Quaint, huh? There’s Commoner, preserved like a bug in the amber of the Sixties, type specimen of an extinct political species.

Pollution, war, and inequality as related issues? But we all know better now, don’t we?