Columns

Last week’s column on hybrid birds requires a correction. I wrote that some years ago an American avocet mated with a black-necked stilt at the Monterey Bay Aquarium, producing a hybrid offspring which was nicknamed “avostilt.” Wrong. According to the Aquarium’s Ken Peterson, the event did not happen there. “Our birds rarely breed, and when they do they breed true,” writes Peterson. 

Back to Google. The misalliance, as it turns out, actually took place at the San Francisco Zoo, in 1971. A couple of avostilts—or, as some prefer, stavocets—have subsequently been documented in the wild. 

That raises a question of nomenclature: what do you call the result of such an interspecies encounter? Some terms are well-established: mule and hinny, of course; coydog, for coyote-domestic dog crosses; liger and tiglon, for captive-bred lion-tiger mixtures. 

Within the last couple of years, a hunter somewhere in the Arctic shot a peculiar bear which showed characteristics of both grizzly and polar bear ancestry. No real surprise, since the two species (grizzlies are actually a subset of brown bears) are close genetically, and since the shrinking of the polar ice has been forcing polar bears to forage onshore where encounters with grizzlies are more likely. The creature was almost immediately dubbed the grolar bear, which seems inevitable once you realize the alternative is pizzly. That’s not something you’d want to call a bear, at least to its face. 

Some recurrent bird hybrids have standard names, in part because they were originally considered to be valid species. Wurdemann’s heron, sometimes seen in the Florida Keys, is a cross between the blue and white morphs of the great blue heron. Two eastern wood-warblers, the blue-winged and golden-winged, consistently produce two distinct hybrid types known as Lawrence’s and Brewster’s warblers. (Blue-wings seem to be genetically swamping golden-wings in the Northeast.) Sutton’s warbler is the offspring of a yellow-throated warbler and a northern parula. On the other hand, there’s no accepted name for the not-uncommon hybrid between our own Townsend’s and hermit warblers. 

It’s been speculated for a long time that some of the mystery birds described and painted by Audubon were hybrids—particularly his 

“carbonated warbler,” although his subjects may have been young male Cape Mays. Audubon also illustrated what he called the Brewer’s duck, a mallard-gadwall cross. 

Apart from the correction, my other reason for revisiting hybrid birds is to report that the Barrow’s goldeneye/hooded merganser (goldanser? or does that sound too much like “pole dancer?” ) has returned to Lake Merritt. It’s a striking bird, with elements of the adult male plumage of both species. What has fascinated me about this bird is that its bill seems intermediate in shape between goldeneye (broad) and merganser (narrow) standards. Mergansers are specialized fish-eaters whose bills have serrated margins to hold their prey. The Lake Merritt hybrid is a mussel-grubber like its goldeneye parent. 

Since it’s a wild migrant, we have no way of knowing if the goldanser has ever produced offspring of its own. Some avian hybrids—the cross between western and glaucous-winged gulls, for one—are fertile, unlike the mule. But I suspect most hybrid birds are one-offs, evolutionary dead ends. In vertebrates, hybridization rarely leads to the formation of a new species 

(barring a few special cases among lizards involving all-female parthenogenic species of hybrid origin.) That phenomenon has been reported for a couple of butterfly species, though, and appears to be a significant driver of speciation among flowering plants. 

Footnote on butterflies: lepidopterists don’t have that many natural butterfly hybrids to work with. In the past, they compensated by naming every recognizable variation within a species, usually for other lepidopterists. Thus in older books like John Adams Comstock’s Butterflies of California you’ll find coinages like “Gunder’s aberrant lady.” Well, who are we to judge?