Monday, July 27, 2015

The Crows Are Taking Over

I was in the back yard filling the dog's dish with water when I heard the hedge shrubbery rustle behind me. "The crows," a voice said. I recognized the voice: it belonged to one of the DMV parking lot guards, who no doubt was on his rounds when he saw me through the leaves. "The crows?" I asked, without looking behind me as I ran the hose. "They're taking over," he intoned ominously.

Indeed, I've noticed over the last month, as summer's heat compounds the drought shredding the local ecosystem, that crows and ravens are getting organized on the hunt for food. They've gotten together before, of course, but I've never seen this scale of organization previously.

California crow populations have increased mightily over the past century, and they may well be the biggest beneficiaries of the drought as other bird populations collapse under the pressure. Here's an article from 2012 in regards to the Bay Area.
Not so long ago, common ravens were uncommon in the Bay Area. A 1927 reference calls them "rare" except at Point Reyes. American crows lived mostly along the Marin County coast, not in the East Bay.

In 1991, Audubon Christmas Bird Counts tallied 17 crows and 54 ravens in San Francisco; 60 crows and 23 ravens in Oakland. The 2011 San Francisco count reported 599 ravens and 566 crows; Oakland had 1,152 crows and 193 ravens.

Remarkable, especially considering that crows, if not ravens, are highly susceptible to the West Nile virus. California Department of Public Health statistics show more dead crows than any other bird species testing positive for West Nile: 1,792 in 2008; 468 last year. (Raven mortality was minor.) The disease devastated crow populations in the East and Midwest, but California populations weren't dented.

...What brings them here? Kevin McGowan of the Cornell Lab of Ornithology notes that they don't get shot in cities; they benefit from both federal protected status and local firearms ordinances. That alone may encourage boldness. Also, he says, cities tend to be warmer than the countryside, and have large trees for night roosting. Urban crows are less likely to encounter their mortal enemy, the great horned owl, and city lights let crows spot owls before the owls spot them.

There's food, too: not so much the landfill smorgasbord (more the gulls' beat) as the fast-food parking lot buffet. "We eat so much out of doors now that these very intelligent birds can access all those food scraps we just drop or toss on the street," said Dan Murphy, compiler of the San Francisco Christmas Count. Some people feed them on purpose, too.

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