My mom called me up one night last week. Her dog was outside, nose to nose with an opossum, and she wanted to know if that was normal. I told her what I knew off the top of my head: that opossums are not true hibernators, and that if they go out to scrounge up some food, they do so at night. The behavior exhibited was normal. She lives down by Appleton, in an area where I know opossums to habituate. But we do not have them up here. Or do we?
The next morning, I headed to the western part of Oneida County because we had gotten just enough snow to run my winter track survey. The first track I came across was unfamiliar to me. At first, I assumed it was a porcupine. Upon closer inspection, I realized that it was not a porky-the heel pads were too small, and there were no quill drag marks. So, I pulled out my track identification book and worked through the process. I came up with opossum.
I can’t imagine an opossum living this far north. There is a great reference book in my office for occasions like this, Mammals of Wisconsin by Hartley H. T. Jackson. It was printed in 1961, a bit dated for some uses, but it gives excellent life history information and historical context. The author was born in 1881, and was living and working at the same time as Wisconsin ecologist Aldo Leopold and naturalized Wisconsinite John Muir, among others. Jackson’s book is a good read, very well-written and with just a touch of humor. I went straight to this book to see what our original wildlife survey results were for this creature. Distribution was stated as the southern half of the state (our current distribution map shows them everywhere but northeast Wisconsin.) The author goes on in exhaustive detail about this animal.
As a biologist, I find opossums fascinating because they are so different from any other animal we have here. It is the only marsupial in North America. The marsupials carry their young in a fleshy pouch; you may be more familiar with distant relatives like kangaroos and koalas. At birth, the blind, naked young crawl from the birth canal about three inches into the pouch, where they attach to a nipple and nurse. As they get older, they ride on mom’s back as she searches for food. The opossum has a fully prehensile tail, meaning it can use the tail to grasp and hang from branches. It has opposable thumbs on the front feet, making it easy to grasp things for eating and climbing. When startled or attacked, an opossum will collapse on its side, drool comes out its mouth, and it poops gross, smelly, green excrement. Known as “playing possum,” this is not an act, but an actual involuntary reaction or reflex.
According to Jackson’s book, early biologists wondered if this animal bred through the nose. The male reproductive organ is two-forked, and the only visible pair of openings on the female is the nostrils. Not to worry, though, this is because marsupial females have two uteruses (uteri) and has nothing to do with the nose at all.
Opossums are nocturnal, hiding in brushpiles, hollow logs or any other small opening during the day. They come out at night to forage, and will eat practically anything, similar to raccoons. In the southern reaches of the country, people hunt and eat opossum, but they are not customarily hunted here. In Wisconsin, opossums are an unregulated animal, much like porcupines and chipmunks.
With the change in our winters and the amount of development over the last 50 years, maybe the habitat has become hospitable enough for the hardiest of opossums. Other wildlife thought to be vulnerable to Northwoods winters, like turkeys, have established their presence here. So what is next? In another 50 years, will we start to see armadillos?
Jeremy Holtz is a wildlife biologist with the Wisconsin DNR and writes a weekly column in the Star Journal. To contact him, call (715) 365-8999.