08 February 2013

Friday Field Notes: All Eyes on the Wolverine

When it comes to wolverines in the news, the media is usually referring to a certain university in Michigan, not the aggressive, thirty-pound weasel that roams the high mountain ranges of the western United States. But following last week's announcement by the U.S. Fish & Wildlife Service that the large mustelids were being considered for "Threatened" status under the Endangered Species Act, even prominent news outlets like the New York Times and the Huffington Post couldn't keep their eyes off Gulo gulo.

The wolverine's scientific name, Gulo, comes from the Latin word for "glutton." However, despite the animal's ability to take prey of considerably larger body sizes than its own, the characterization of the wolverine as a glutton may actually be the result of a false etymology. Indeed, some researchers believe that the Swedish word used to describe wolverines (which in English translates to "mountain cat") is very similar to the German word vielfrass, which means "devours much"--and the rest is history. The common name "wolverine" is derived from the German word wolvering, which loosely translates to "little wolf" or "wolf-like."

They might look cute, but I've heard they have a bit of a temper.
A more appropriate name for the wolverine would be "little bear." In the rare event that people actually do see a wolverine in the wild (usually from some distance away), they often mistake them at first for bear cubs. It's hard to blame them: wolverines can be over three feet long and weigh upwards of 70 pounds! At nearly twice the size of their cousin the fisher (Martes pennanti), it becomes obvious that wolverines are not your ordinary weasel. When it comes to meal time, wolverines are actually more like bears than weasels. While prey often consists of small mammals such as shrews, voles, and rabbits, wolverines have been known to take animals as large as white-tailed deer, elk, and occasionally moose. This fact, combined with the fearless manner in which they have been observed competing with wolves and bears for carcasses, has earned the wolverine the title of "nature's most ferocious animal."

Incredible feeding behaviors aside, the most impressive aspect of the wolverine might be its propensity for movement. With massive, snowshoe-like feet, wolverines can move quickly and gracefully over snow-covered alpine environments. Case in point: a wolverine collared by researchers near Jackson, Wyoming, once traveled to Pocatello, Idaho, (a distance well over 100 miles) and back in under three weeks. Apparently not tired of life on the road, he later made another 100+ mile trip southeast to Wyoming's Wind River Range, then took a detour to the Salt River Range on the Wyoming-Idaho border before returning north to his home.
A wolverine family roams the backcountry of Glacier National Park

Don't let this deceive you; wolverines aren't wanderers, rambling through the mountains without direction. Rather, they are animals with massive home ranges, sometimes greater than 200 square miles, living in very low densities. In the odd event that they do manage to run into another wolverine and develop a romantic interest (which will become a lifetime partnership), the female digs a large den in deep snow in winter before giving birth to a litter of two to three in early spring, which the family will occupy until late spring/early summer. Thus, the presence of deep snow, both for movement and denning, is a critical part of wolverine life history.

It is these strict habitat needs--particularly the need for stable snowpack--that now have prominent scientists and researchers discussing whether the animal warrants the heightened protection of Endangered Species Act listing. Some climate models predict that suitable wolverine habitat will decrease by almost two-thirds before the end of the century if warming and reduced snowpack trends continue. It is a particularly damning revelation for the wolverine, whose population is just beginning to recolonize habitat in the lower 48 after near-extirpation, and now numbers somewhere between 250 and 300 individuals. In 2008 and 2009, a few ambitious wolverines wandered as far south as Utah and Colorado, the first time they have been observed in either state in nearly a century. Now, the strides being made by wolverines to re-establish themselves in the West are in danger of being nullified by climate change.

If ESA protection is granted to the wolverine (a decision that will be made in about three months time, once the comment period closes), researchers would be allowed to introduce an experimental population in Colorado, a region which offers plenty of suitable habitat, yet due to connectivity issues, has not been naturally recolonized. It is unknown if similar reintroductions/translocations would be permitted in other areas of the western US. Due to the nature of wolverine habitat (high, cold, rocky, dry places), ESA listing would likely have little economic impact, though it would certainly put an end to Montana's trapping season, which currently allows for the taking of five animals annually. It is worth noting that the 2012-2013 season was suspended by a U.S. district court in anticipation of the ESA listing proposal.

While the future of the wolverine is uncertain, there is little doubt that Montana will be an important part of that future. Today, roughly half of the lower 48's estimated population of 300 wolverines lives within the Big Sky state. The mountains of northwestern Montana, particularly Glacier National Park and the nearby Bob Marshall Wilderness Complex, are a stronghold for this fiery weasel. Conserving wolverines, therefore, is intimately tied to the conservation of our backyard.

01 February 2013

Friday Field Notes: On Bergmann's Rule, Ratios, and the Art of Staying Warm in Northern Climates

When MNHC's distinguished naturalists enter elementary school classrooms throughout western Montana this February for their monthly visit/natural history lesson, they will be discussing a fairly important ecological principle with 4th graders: Bergmann's rule. First articulated by German biologist Christian Bergmann (hence the name), the principle states that within a broadly distributed species or taxonomic group, an organism's body mass tends to increase with an increase in latitude (and the corresponding colder climate). While this principle has been most widely applied to mammals and birds, there are also examples of cold-blooded species that conform to the rule.

Why is such a principle observed in nature, you ask? Fundamentally, it is a function of larger animals exhibiting a decreased surface-area-to-volume ratio. Thus, larger-bodied animals lose less heat per unit of body mass, a characteristic that becomes vitally important in places like Montana where winters are long and cold. The following graphic helps better display this relationship:

Graphic displaying the mathematics underlying Bergmann's rule.

The important thing to note is the red text: While the larger cube has a considerably higher surface area, its volume has increased proportionately even more, thus lowering the surface-area-to-volume ratio.

Now, I know what you're thinking: Surface-area-to-volume ratios are a bit much for 4th graders. Most of us hadn't even heard of Bergmann's rule until our first college-level ecology course. But the science and mathematics underlying this stalwart of ecology can be easily explained and visualized. Consider this simple experiment, best suited for a brisk (32 degrees F or less) Montana winter day:
  • Simultaneously fill up two cans of different sizes (i.e., a coffee can and a soup can) with near-boiling water. Place a thermometer in each can, and record the initial temperature.
  • Place both cans outside. Record the temperature of each can every minute for approximately ten minutes.
  • Afterwards, compare the change in temperature of the cans. The larger can should be significantly warmer than the smaller one, a result of its lower surface-area-to-volume ratio.
This simple experiment is a great way to test and conceptualize Bergmann's rule, and sheds light onto why being bigger is better when you live in northern latitudes. This fundamental relationship between surface area and volume explains why animals such as deer, elk, moose, and bears get larger as you move further north within their range. In some cases, the size difference can be quite dramatic. Male grizzly bears, for example, whose average weight is in the range of 500-1000 pounds in the Interior West, can reach up to 1,500 pounds in Alaska! In white-tailed deer, an incredibly far-ranging species, a similarly dramatic change is observed:

Bergmann's rule exhibited in white-tailed deer

So, if you're feeling guilty about those extra pounds you're still carrying around from holiday feasts or winter vacations, look on the bright side: You're going to stay much warmer this winter than you would without them!