Friday, February 05, 2010

Nine-banded armadillos expanding horizons in Illinois

Nine-banded armadillos expanding horizons in Illinois

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At this time of year I sometimes wonder what could have possessed some of our distant African ancestors to migrate north far enough to experience the harshness of winter. What were they thinking? And why didn’t they go right back to where the weather was warm year-round at the first opportunity?

It strikes me that the same thought might occur to some nine-banded armadillo in the future. You may think of armadillos as creatures of southern states, and the fact is they crossed the Rio Grande into Texas only as recently as 1850. But armadillos are today expanding their range farther north than ever before, settling in states—including Illinois—where winters are severe enough to really test their limits.

2002 Joyce Hofman, a biologist who recently retired from Illinois Natural History Survey, established a database of armadillo sightings in the Prairie State. She was prompted to do so by the gift of a road-killed armadillo that had been picked up in southern Illinois by a colleague and in part by a scientific article that anticipated armadillo expansion into the state. [Photo: An armadillo digs with its head down in leaf litter. Inset shows the face of an armadillo. By Michael Jeffords.]

Hofman has included in the database sightings going back as far as 1990. By September 2009 she had collected reports of at least 194 armadillos in Illinois, 90 percent of them from after the year 2000. Most of the armadillo observations have come from the part of the state west and south of Effingham, with the greatest concentrations in the counties along the Mississippi River.

How do armadillos get to Illinois? They have been observed as stowaways in rail cars and on barges, so it is likely some of them are transported here that way. Others may simply walk across bridges over the rivers bordering the state on their own. It is less likely but possible that others swim here, perhaps using islands to break up the journey.

Here are some things you might be interested to know about our quirky new neighbors.

Armadillos are surprisingly fast for such ungainly looking creatures, and they can dig into the ground quickly if there’s not an existing burrow nearby for escape. When startled, armadillos sometimes jump straight into the air. This defensive strategy may confuse predators, but it’s not a good response when the approaching threat is a fast-moving vehicle.

Armadillos don’t float naturally, so they cross small bodies of water by walking across the bottom, like divers wearing weights. When they must swim, they can make themselves buoyant by gulping air to partially inflate their intestines.

Armadillos typically give birth to identical quadruplets every year, and they can delay pregnancy at the earliest stages to ensure that young will not be born until weather conditions are favorable.

And of course, armadillos are the only North American mammals that grow their own armor.

The northward expansion of armadillos will eventually be stopped by cold. They can tolerate subfreezing temperatures by hunkering into a burrow for a period of days. But as their energy stores are depleted they must seek out food, insects and other small creatures they find by digging in the earth. Where the ground stays frozen for too many days in a row during winter, armadillos are unable to dig for food and can’t survive.

If you see an armadillo in Illinois, you can help add to the store of information about them by sending an e-mail with the time, date, and location of your sighting to Joyce Hofman via