Friday, December 14, 2007
California's possum diaspora
The Virginia opossum was one of my last camera trap visitors at Point Reyes National Seashore. As reported in my last possum post, this curious possum was also attracted to the electronic flash and gazed inscrutably at modern technology.
The Virginia opossum is one of California's recent mammalian immigrants, but the history of its colonization raises many questions.
What we know is that California's ancestral possums came from MacDonald County, Missouri and Jackson County, Tennessee, and probably other places as well, though no one knows for sure.
Those pioneer possums were tough. It would have been a grueling cage-rattling trip on the transcontinental railroad, but they could have toughed it out during the warm months. Sea travel would have taken more time, and seems less likely, but their sprawling "sea-legs" would have served them well.
At the turn of the last century the Golden State had much to offer its citizens in the way of wildlife, including grizzly bears, but her settlers from the South missed their possums. Possums may not be challenging quarry for the hunter, but memories of baked possum and sweet taters summoned mouthwatering cravings.
Early Californians kept penned possums for food, but they didn't keep them for long. I suspect the possum farmers soon grew tired of their chores, and decided it would be a lot easier to harvest wild possums. Maybe that's why one W.D. Watkins set five Missouri animals free about 3 miles south of San Jose. That was back in 1900. We don't know if they survived, but if they did, rest assured they went forth and procreated. In 1910 several more possums are said to have escaped from a San Jose jeweler and possum fancier. His seven possums came from Tennesee. Apparently possum owners in Los Angeles also had a hard time keeping their stock penned.
By 1913 one hundred opossums had been captured in the greater San Jose area (Santa Clara County), and by 1915 they had apparently made their way over the coast range into the San Lorenzo Valley in Santa Cruz county. This route would have led venturesome possums to the coast, and to easy routes north and south.
An attempt to introduce possums to mountainous Shasta county failed around 1932, but possums from San Jose spread into the San Joaquin Valley, circumnavigated San Francisco Bay, and thence colonized the northern coast range, the Sacramento Valley, and the northern foothills of the Sierra Nevada.
You are looking at a descendent of those hardy pioneer possums. The foggy windswept coastal scrub of Point Reyes is a far cry from the bottomlands of the south, but like the rest of us here, Br'er possum is quite at home.
Gardner, A.L. and M.E. Sunquist. 2003. Opossum, Didelphis virginiana. Pp 3-29 in Wild mammals of North America (G.A. Feldhamer, B.C. Thompson, and J.A. Chapman, eds.). The Johns Hopkins University Press, Baltimore.
Grinnell, J., J. Dixon, and J. Linsdale. 1937. Fur-bearing Mammals of California. University of California Press, Berkeley.
Ingles, L.G. 1954. mammals of California and its coastal waters. Stanford University Press, Stanford, California.
Lidicker, W.Z., Jr. 1991. Introduced mammals in California. Pp 263-271 in Biogeography of Mediterranean Invasions. (R.F. Groves and F. di Castri, eds.) Cambridge University Press, Cambridge, UK