By Wendy Langhans
My Dad was (and still is) an avid duck hunter, so I grew up around hunting dogs. At an early age, I learned the two fundamental “Wet Dog” rules of thumb. First – the more a wet dog likes you, the closer it gets to you before shaking off the water. Second – you can’t outrun a wet dog. And just last week, I discovered a third rule of thumb – the bigger the mammal, the slower the shake.
Let’s start by asking a basic question – why do mammals shake themselves when wet? The short answer, of course, is to dry themselves. Mammals are, by definition, furry creatures, and water adheres to their fur because of surface tension. The “Wet Dog Shake” is a series of rotations around the central axis of the body, beginning with the shoulders and extending through the trunk to the hips. This rotational shaking creates the centripetal force needed to overcome the surface tension and eject the water droplets from their fur.
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But why do mammals need to dry themselves? Remember the last time you forgot your umbrella on a rainy day? How cold were you? A wet mammal loses heat faster than a dry animal, because water is a better conductor of heat. According to this quote in “Science News”, “If a dog couldn’t dry itself, we calculated that it would have to use 25 percent of its daily calories to heat its body to get rid of the water”. So an animal that remains wet will expend metabolic energy to stay warm or it will suffer from hypothermia.
Mechanical Engineers at the Georgia Institute of Technology recently published a study of the oscillatory motion made by wet mammals. They videotaped 40 wet hairy mammals of 15 species shaking themselves dry (click here to see a video). They found that in mammals, the larger the radius (chest size), the slower the frequency of the shaking. According to the Professor Hu, “All the animals have to reach the same speed [which is equal to frequency times radius], but because the larger animals have a larger radius, they can move at a slower frequency.” A mouse, for example shakes at a frequency of 27 Hz, or 27 times a second. A Grizzly Bear shakes at 4 Hz. And a Labrador Retriever shakes at about 4.6 Hz.
I hope those engineers were smart enough to bring a change of clothes with them to the lab. I’m sure there were times when they got sopping wet.
Upcoming Outdoor Events:
Saturday, November 20, 8:00-10:00 AM, Morning Bird Hike at Towsley Canyon. Towsley Canyon is a year-round home for many birds. For the permanent residents summer brings the heat and winter the rains. Amazing, birds find a way to tolerate the challenges and celebrate the rest. Beginners welcome, bring binoculars. For directions and trail maps, click here.
Saturday, November 27, 10:00-12:00 AM, Native Plants and Native Uses, at East/Rice Canyon. Not all shopping malls have walls. The local Native Americans were savvy shoppers, finding food, clothing and shelter right in their own backyard. For directions and trail maps, click here.
Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at firstname.lastname@example.org for time and place.
Wednesday mornings, November 3, 10, 17, & 24.
Saturday mornings, November 13 & 27.
You can listen to stories like this every Friday morning at 7:10 a.m. on “The Hike Report”, brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.
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