Thursday, February 21, 2013

Predator and Prey

Ice pellets sting my cheeks as I whizzzzz down a steep slope on my skis. This roller coaster hill at the Rock Lake ski trails zooms me all the way up to the top of the next knoll. As I glide over the crest and begin to pick up speed on the next downhill, I notice tracks in the fluffy snow on the side of the trail.

On several previous occasions, I have purposely wiped out so I could go back and look at tracks, but just a quick look at these allows me to guess their maker. Two feet, each less than an inch wide, planted side-by-side, one slightly ahead of the other, and with an impressively long leap between pairs of tracks. Must be a weasel.

We have three small weasels in Wisconsin—the least weasel (the world’s smallest carnivore!), the short-tailed weasel, and the long-tailed weasel. Males are quite a bit bigger than females in each species, so a male short-tailed weasel could be just as big as a female long-tailed weasel. I could not identify these tracks to species, but all three share some amazing characteristics.

As extremely active critters with heart rates of up to 500 beats per minute and correspondingly high metabolisms, weasels must eat about 30% of their bodyweight each day. Fortunately, they are adaptable predators. Rabbits, mice and other small rodents are favorite prey, and weasels will even follow mice into their burrows. A flexible spine allows weasels to maneuver easily in tight spaces; sensitive whiskers and a great sense of smell guide weasels in the underground darkness; and taking over the den of their prey saves them the effort of digging their own burrow. While this may seem a bit harsh, weasels are important predators that keep rodent populations in check.

Weasels are not at the top of their food chain, though, and risk becoming prey to hawks, owls, snakes, housecats, foxes and more. Luckily, protective coloration gives them an advantage in the snow. Weasels completely shed their fur and grow a new coat twice a year. As autumn days grow short, one transition begins. If temperatures are cold enough, a white coat grows in.  If the temperature is warmer, or variable, the coat may have patches of white and brown. This helps them adapt to variable weather patterns and new habitats. The lengthening days of spring trigger the growth of the transition to their brown coat.

Through all seasons, short-tailed and long-tailed weasels wear black tips on their tails. While you might think that this would stick out like a sore thumb and compromise their camouflage, it actually provides an excellent distraction for their predators. In 1982, Roger A. Powell did an ingenious study at the Brookfield Zoo and published his findings in the journal The American Naturalist. He used model weasels of various sizes with and without black-tipped tails, and real red-tailed hawks that were trained to attack them.

Powell found that “Long-tailed weasels with tail spots and least weasels with no spots were missed significantly more frequently by each hawk than the other color-size morphs.” He also recorded that “Observers occasionally noted that hawks attempted to grasp the tail of the long-tailed, tail-spot morph but were unable to hold the tail because of poor dexterity and tail thinness; or hawks appeared to check their attack and miss at the last moment as though they had been surprised by some aspect of the weasel model.”

Thus, the tail spot on the long-tailed and short-tailed weasels serves to deflect attacks away from vital organs. Deflection marks are common in insects (think about false eyes on butterfly wings or false heads on caterpillars), but no other mammals we know of use them.

Wouldn’t the least weasels, who lack tail spots year round, be at a disadvantage? Powell concluded that their small size makes it difficult for predators to see them in the first place, and with much shorter tails, the tail spot would be too close to vital organs for comfort.

Weasels’ defensive strategies do not end with deflection marks and camouflage. Erratic movements, quick direction changes, and snow tunnels also help them evade predators. Lucky for me, all I need to catch is a glimpse of one weasel’s tracks. Just that gives me something wonderful to chew on as I glide up and over the next snow-covered hill.

Weasels, sugar maples, gall flies, ticks, wolverines, moose, skiers, snowshoe hares, lynx. We all LOVE winter. During Birkie week, the Museum is creating an exhibit called "We LOVE Winter," that will highlight the fascinating winter adaptations of animals. Come visit, learn more about critters who share your love for winter, and gain a new appreciation for this challenging and delightful season. Why do YOU love winter? Send me your reason(s), your first name, and age, and they will be posted in the Museum!

For over 44 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M. The current exhibit, STAR POWER: Energy from the Sun, opened in May 2012 and will remain open until April, 2013.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

No comments:

Post a Comment