Home & Garden Columns

California Ravens: A Unique and Complex Species By JOE EATON Special to the Planet

Tuesday February 28, 2006

Ravens are complicated birds. Spend enough time with them and you’ll learn that there’s no such thing as “the raven”—a standard one-size-fits-all set of behavioral traits. They’re as wonderfully various as we are. 

Case in point: Bernd Heinrich, in his classic books Ravens in Winter and Mind of the Raven, talks about how wary and unapproachable the ravens in his Maine woods are. But that’s New England; elsewhere they’re entirely different. In the far north, they hang around native villages and hunting camps; there’s usually a raven or two underfoot in John Straley’s mystery novels, set in Alaska. I’ve been panhandled by ravens at the Grand Canyon and in the Petrified Forest. And last week at Point Reyes I had an unusually close raven encounter. 

We were having lunch at a picnic table at Drake’s Beach after a hike to Chimney Rock when the first raven, sporting a silver band on his left leg, flew in. He (as we inferred later) gave a series of soft grawks, and a second bird joined him. They billed a little, and the unbanded bird started preening the banded one; this was evidently a couple, with a breeding territory nearby. Then they turned their attention to our cars; the presumed male went up and pecked at one of the license plates. All this while we were finishing our sandwiches a couple of yards away and keeping up a running commentary on the action. The ravens seemed unconcerned with our presence. But when my friend wondered out loud if they’d like a carrot and reached for his bag of carrot sticks, one of the birds gave an indignant croak and both of them flew away, toward the visitors’ center. 

I had no idea that ravens were repelled by carrots. They’re not vegetarians, of course; they’ll happily scavenge from carcasses, and I once saw one kill, dismember, and eat a fair-sized pocket gopher. (Heinrich says his northeastern birds avoid roadkill; that’s not at all true of their western cousins). The ravens in the Tower of London eat apples, among other things. Maybe it was just that the carrots were unfamiliar objects, and that these mature birds were more conservative about novelties than they were as adolescents. 

But their tolerance of our proximity up until then was what impressed me. It could just be that the ravens in western parks have learned that no one is going to shoot at them. With their large (for birds) brains and complex social systems, ravens display an almost primate-like behavioral flexibility. They’re what the late biologist Ernst Mayr called “open-program” organisms, modifying their behavior as they learn about their environment.  

Heinrich feels they have what can meaningfully be called culture: shared learned behaviors—dialects, foraging techniques—that differ from group to group. His experiments with captive ravens have proved them capable of solving problems through insight. As far as I know, there’s no evidence of tool use by ravens—but nothing these birds do would surprise me. 

They’re adaptable enough to find homes in our cities. The Bay Area has experienced an urban raven boom in the last couple of decades, along with an even larger influx of crows. Ravens have become a familiar sight in Berkeley, although I don’t know where they’re nesting. There’s no love lost between the ravens and the crows, probably because of both species’ propensity for nest robbing. The local crows have a specific flat, nasal call that appears to mean “Here comes a raven—let’s chase it out of the neighborhood.” 

Given all that, though, there may be something different about California ravens. Ravens occur all through the Northern Hemisphere, south to Nicaragua, India, and North Africa, and all the populations looks pretty much alike, with minor variations in size. But as it turns out, that uniform appearance masks a deep genetic faultline.  

A few years ago, a group of biologists including William Boarman of the U.S. Geological Survey and John Marzluff at the University of Washington compared mitochondrial DNA samples from 72 ravens, collected throughout the species’ range. The specimens sorted into two lineages, or clades: a California clade and a Holarctic clade for the rest of North America, plus Eurasia, with a 5 percent genetic difference between them. “We have found that ravens from Minnesota, Maine, and Alaska are more similar to ravens from Asia and Europe than they are to ravens from California,” said Boarman. He speculated that the split may date back to two million years ago, when the ancestral California population was separated by glaciers from ravens in the rest of the continent. That scenario would be consistent with the evolutionary history of other North American birds, including the California-endemic yellow-billed magpie and the more widespread black-billed magpie. 

Boarman and his colleagues weren’t ready to call the California raven a new species. There’s a wide zone of overlap between the two clades in the Great Basin, from Washington and Idaho down to northeastern California, and it’s not clear whether Holarctic-clade and California-clade ravens are interbreeding there. If so, the two clades may be dissolving into a common gene pool. But if they’re not, that would mean the two groups are acting like distinct species, with some kind of behavioral barrier as an isolating mechanism. Maybe it’s vocal (Holarctic-clade ravens just sound wrong to California-clade birds?), or a subtle difference in habitat preference.  

So the jury is still out on the species issue, pending more research in the contact zone. It’s remarkable how much there still is to learn about this widespread and well-studied bird. Maybe someday science will even be able to account for that fear of carrots.