California Has Two New Bird Species. One's in Your Yard Right Now.

California is home to two new bird species — and you've seen at least one of them hundreds of times. Ornithologists have determined that two widespread populations of the familiar Western scrub jay (Aphelocoma californica), one of the state's most common birds, are different enough from each other to merit splitting the species in two.

Scrub jays along the Pacific coast will now be called California scrub jays, which will keep the Western's scientific name, while the paler, smaller-billed jays in the far eastern reaches of the state are now officially referred to as Woodhouse's scrub jay, or Aphelocoma woodhouseii.

The split was made as official — or at least as official as such things ever get — when the new species was added to the 2016 edition of the American Ornithologists' Union's Checklist of North American Birds. The Checklist, which is updated every year, is regarded by both scientists and recreational birders as the authority on North American bird taxonomy, and its annual revision is anticipated avidly by birders.

But the split of the Western scrub jay into two species is no surprise: the Woodhouse's scrub jay has long been considered quite distinct from its coastal cousins, and scientists have talked about calling the Woodhouse's scrub jay a distinct species from coastal jays since at least the 1940s. And it's unlikely that this year's split will be the last scientific rearrangement for the scrub jay.

If you don't remember actually having seen a scrub jay of either species, you've almost certainly heard one. These raucous, engaging members of the crow family are anything but retiring. Here's a California scrub jay making its presence known in Santa Barbara:

It's not hard to tell scrub jays from their cousins the Steller's jay, which are the only other blue-colored jays native to California: Steller's jays, known to science as Cyanocitta stelleri, have black heads with pronounced crests. Scrub jays of whichever species lack crests, and their heads are mainly blue up top, with a dark eye patch that can look either black or dark blue depending on the light.

The differences in appearance between California scrub jays and Woodhouse's scrub jays are a little more subtle: Woodhouse's are a paler blue overall, and are less likely to have a distinctive blue breast stripe — a "necklace" — than their coastal relatives. One of the more interesting differences between the two species seems to have evolved as a result of the birds' different geographical ranges: coastal California scrub jays' oak woodland habitat offers a steady crop of nutritious acorns, and the birds have evolved heavy, hooked bills that make short work of acorn's tough shells. Woodhouse's scrub jays live in the more arid interior, where piñon pines and junipers offer the most reliable source of food. Woodhouse's have narrower bills, which presumably evolved due to the birds' need to extract pine nuts from their cones.

That difference in geographic range is actually the easiest way to distinguish between the species. California scrub jays range from the environs of Seattle along the coast to northern Baja, with an outlier population in southern Baja. In California, they occupy the western half of the state, from the coast well uphill into the west side of the Sierra Nevada — the birds are common camp robbers in Yosemite National Park.

Woodhouse's scrub jays are relatively uncommon in California: their population stronghold is in the semiarid mountain forests of the Colorado Plateau, with other big populations in the Texas hill country and mainland Mexico. Woodhouse's scrub jays do range into California's eastern edge on a regular basis; there just aren't a lot of them here at a time. The consummate birder Kenn Kaufman has mapped the ranges of the two new species in his article on the split on Audubon's website, and really the easiest way to tell whether the scrub jay in front of you is a California or a Woodhouse's is to look at the map and see whether you're in Woodhouse or California territory. Unless you're in the stretch of desert between Reno and Carson City, Nevada, the map is pretty much a slam dunk.

Kaufman points out that the abundance of each new species in parts of the west is a boon to those birders compiling life lists, an acquisitive hobby whose practitioners can make Pokémon Go players look like pikers:

This isn't the first time ornithologists have split off new scrub jay species. Field guides once listed both the Florida scrub jay and the Santa Cruz Island scrub jay as members of the California scrub jay species. Both were declared to be separate species in 1998.

This current split between California and Woodhouse's scrub jays may not be the last. Though discussion of splitting the scrub jay has been happening for some time, the AOU's decision was mainly prompted by a 2014 study of scrub jay genetics, led by biologists from Occidental College's Moore Laboratory of Zoology, that also suggested that scrub jay populations in southern Mexico may merit being declared a new species as well. It's likely North America may see even more new species of scrub jay before long.

There's other news of interest to California birders in the 2016 Checklist: the Leach's storm-petrel, a small, dark seabird with a wide distribution in the Northern Atlantic and Pacific, has had two new species split from it: the Townsend's and Ainley's storm-petrels. Both new species nest on remote islands off the Pacific coast of Baja California, making it possible that Southern California birders might see them. But distinguishing the new species from the much more common Leach's storm-petrel and from each other is extremely difficult, so it's likely that this new split will vex birders.

And a name change of one of California's most prominent birds won't make much difference to birders, but will probably delight classicists. The sandhill crane, a four-foot-tall bird that winters in wetlands in the Central Valley and near the Salton Sea, has long been known scientifically as Grus canadensis. Recent genetic work has prompted scientists to rearrange the cranes: the whooping crane and common crane are staying in Grus, but scientists have determined that sandhill cranes are too distantly related to other cranes to share a genus. So sandhill cranes get a new genus, Antigone, named for Oedipus' daughter and half-sister. 

But while reassignments like these happen in pretty much every annual update of the checklist, it's not all that often that they affect a species as common as the scrub jay. So next time you hear that raucous cry through your window, reflect on the fact that we have plenty to learn about wild species, even if they're living right under our noses.

For the record: This story has been updated to include a link to the study that prompted the AOU's decision.