Election Section

The taxonomists have been at it again, but this time they’ve done something that makes intuitive sense. Every couple of years the American Ornithological Union comes out with a supplement to its checklist of North American birds, with name and status changes. 

And birders often wince at the results: either “lumps”—two or more species merged into a single species—that reduce their life-list totals, or “splits” that produce lookalike new species almost impossible to separate in the field. There are always rumors in advance of the new supplement: Is this the year they’ll split the fox sparrows? Finally lump the northwestern crow? Bring back the Harlan’s hawk? 

This year the ornithological powers-that-be decided to break up the Canada goose. They used to recognize 11 subspecies within this common and widespread species, ranging in size from the big honkers to dinky mallard-sized forms. (What’s a subspecies? Basically a population that’s physically distinctive in some way but not so much so that it can’t interbreed with neighboring populations. It’s a slippery category, and some taxonomists would like to scrap it altogether. Often the difference between species and subspecies status is a judgment call. Is the island scrub-jay of Santa Cruz Island, which never has the opportunity to interbreed with the mainland western scrub-jay because neither form will fly across the Santa Barbara Channel, a “good” species? The AOU says so, based on differences in size and plumage and genetic distance. And this kind of thing matters, since subspecies—like the northern spotted owl—can be given protected status under federal and state endangered species laws). 

Back to those geese, though. After the split, seven of the larger subspecies are still known collectively as the Canada goose; four of the smaller subspecies now comprise the cackling goose species. 

The former Aleutian Canada goose, one of the few endangered species that has recovered sufficiently to be downlisted, is now the Aleutian cackling goose. And the subspecies that used to be called the cackling Canada goose, or cackling goose for short? David Allen Sibley, the field identification maven, is calling it the cackling cackling goose. I hope this doesn’t catch on. 

For California birders, it’s easy enough to tell the two species apart. 

A cackling goose in a flock of Canadas stands out like I would among the Golden State Warriors. Its head shape is distinctive: rounder, with a stubbier bill. Aleutian cackling geese, which turn up in the Bay Area during their migrations between their Arctic breeding sites and their wintering grounds in the San Joaquin Valley, are further distinguished by a white ring at the base of their black necks. 

(Cackling cackling geese used to winter in California as well, but most now stop off in Oregon). And there’s a vocal difference: Canadas, AKA honkers, honk; cacklers cackle. Where identification gets tricky is in the Central Flyway, where the winter ranges of the lesser Canada goose and the Richardson’s cackling goose overlap. But that’s not our problem. 

Birders and goose hunters have been aware of the different size categories of “Canada” geese for a long time. Why did it take the ornithological establishment so long to catch up? It seems that what prompted the split was a genetic study mainly focused not on the North American geese, but on their relatives—living and extinct—in Hawaii. 

If you’ve ever visited Hawaii Volcanoes National Park, you’ve seen the signs exhorting you not to feed or run over the nene—the only living Hawaiian goose species, and the state bird. (I spent a nene-less morning in the park; my only nene turned up at the Big Island Country Club on the Kona side, on the 12th hole, near the water hazard. Geese love golf courses—all that short grass, ready for cropping. Golfers, however, do not love geese). Palaeontologists have also found remains of extinct geese on Maui and the Big Island. The latter species, four times the size of the nene, was apparently flightless, with a massive tortoise-like beak that it must have used to feed on tougher vegetation than grass.  

To sort out the evolutionary relationships among the Hawaiian geese and their possible North American ancestors, scientists from the Smithsonian’s National Museum of Natural History, Oxford, and Boston University compared samples of mitochondrial DNA, the stuff we all—geese and humans—inherit from our mothers. 

Since it seems unaffected by natural selection and accumulates mutations at a predictable rate, mt DNA is a handy tool for identifying evolutionary next of kin and determining when different lineages diverged. Their study included the living nene, the extinct giant Hawaii goose and the Maui goose, five Canada goose subspecies (two large, three small), and the barnacle goose of northern Europe, a bird that was once considered edible during Lent because of the folk belief that it was the mature stage of the gooseneck barnacle. 

The results? All three of the Hawaiian goose species appear to be the descendants of a single founding population of large Canada geese that reached the islands about 890,000 years ago. On the older islands, the grazing/browsing niche was already occupied by oversized flightless ducks, the moa-nalos. But when the Big Island formed some 400,000 years later, that niche was wide open, and the giant Hawaii goose took advantage of it.  

The scientists also found a deep divide between the large-Canada and small-Canada lineages, and a close relationship between the small Canada geese and the barnacle goose. They concluded that the “Canada goose” was actually a taxonomic grab bag, containing at least two distinct species. And the AOU followed up on that with this year’s revision.  

So those birders who keep life lists, and who had seen one or more of the small-Canada subspecies now separated as the cackling goose, got to add a new species without a trip to Attu, or even Point Reyes. Think of it as an ornithological stock split. (The smart money is keeping an eye on the warbling vireo.) 

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