Nature Journal: Opossums are highly adaptive creatures

An article in this month's issue of "Smithsonian" magazine entitled "A Few Miles of Land Arose From the Sea -- and the World Changed" by John F. Ross got me thinking about opossums. The article details the significance of the appearance of a land bridge (the Panamanian isthmus) between North and South America approximately three million years ago. Some scientists are now viewing that "as perhaps the single most important natural history event since the death of the dinosaurs 65 million years ago."

And they may be right. For one thing, the land bridge rerouted ocean currents, so profoundly altering the northern hemispere's climate it may well have triggered the Ice Ages that began two million years ago. The land bridge allowed numerous animals (fox, deer, spectacled bear, tapir, spotted bear, etc.) to pass from North into South America.

Are possums dangerous?:They can be, but they're also good for your backyard.

Then, after modern humans crossed over the Bering land bridge between North America and northeast Asia about 14,000 years ago, their ancestors could access South America via the Panamanian bridge.

The Bering land bridge would not have been created in the first place without the extensive ice caps precipitated during the Ice Ages. These sheets of ice (10,000 feet thick in places) that extended as far south as Pennsylvania 18,000 years ago took up so much of the earth's water that ocean levels were lowered several hundred feet.  No Panamanian isthmus, no Ice Age, no Bering land bridge, no American Indians, no 'possums in our southern woodlands.

Of the numerous critters that trekked northward over the isthmus, the lowly 'possum has been the most sucessful because it has been the most adaptable. Humans have not stemmed its progress, which has now reached into Canada.  Our barns and outbuildings provide den sites. Our garbage is a never-ending source of nourishment.

They may have small brains and be a touch dim-witted, but 'possums can find food. And they can remember exactly where they found it in the first place, which to my way of thinking is the ultimate sign of intelligence.  One researcher tested for ability to remember which of four runways was connected to a food box. The 'possum scored better than cats, chickens, dogs, goats, pigs, rabbits, rats and turtles, although somewhat less well than humans.

Nature Journal: Unusual birds at your winter feeder? Blame 'irruptions'

'Possums can seemingly adapt to any situation.  Although they are not immune to the bites of Old World snakes such as cobras and puff adders, they have developed immunity to the Crotalinae subfamily of snakes, which includes the very ones encountered in the Deep South: rattlesnakes, copperheads, and cottonmouths.  They have carried this specific adaptive response to an environmental threat one logical step further. 'Possums eat snakes with impunity. In some areas of the country, copperheads constitute up to six percent of the 'possum's diet.

But when faced with a situation it can't handle, a 'possum does what it's most famous for. It "plays 'possum" by curling on its side, closing its eyes, lolling out its tongue, and lowering its heartbeat in feigned-death posture. It can remain in this state for up to six hours. Once the danger has subsided, the 'possum picks itself up and goes about its two main items of business: finding food and reproducing.

More from Nature Journal: Be careful when identifying and ingesting mushrooms

The only menance 'possums seem to be unable to adapt to is the automobile. They are slain by the hundreds of thousands every year by onrushing vehicles during the nocturnal hours. Caught in the headlights glare they freeze and are doomed.  It's too late to "play 'possum."

But the automobile is a new challange.  Let's give these adaptive critters a little more time to form a response.  Wonder what it'll be?

George Ellison is an award-winning naturalist and writer. His wife, Elizabeth Ellison, is a painter and illustrator who has a gallery studio at 155 Main St., Bryson City. Contact them at info@georgeellison.com or info@elizabethellisongallery.com or write to 3880 Balltown Road, Bryson City, NC 28713.

This article originally appeared on Asheville Citizen Times: Nature Journal: Opossums are highly adaptive creatures