|Measuring the straddle or width|
of a black bear trail
As the photo to the left shows, we used Popsicle sticks and toothpicks to outline the deep, habitually used footfalls (I went into a little detail on an earlier post as to how we decided on the placement of the track within the deep impression). Then a wooden ruler could be placed on the edge of two tracks in order to properly measure the straddle or width of the trail. For the stride, we measured from the rear of one footfall to the rear of the next. In other words, we measured the distance from a right foot to a left foot, not a right to a right. Some authors would call this a step rather than a stride. We only measured a small portion of the habitualized trail. All measurements are in inches:
Stride (or step): 27, 26.75, 23.25, 26.5, 18
Straddle (or width): 15.75, 14.25, 17, 15.5, 17.38, 15.5
For a direct register walk, Rezendes (1999) gives a range of 17-23 for stride and 9.5-14.5 for a straddle. Elbroch (2003) posts numbers only slightly different at 17-25 and 8-14 respectively. Three of our five stride measurements exceed even Elbroch's larger figures. In addition, five of six straddles are above what would be expected. These results alone are interesting as they suggest the bear is not walking in a "normal" walk when creating these trails (or at least this one segment of this particular trail). However, there is a greater significance to these numbers that Nick pointed out to us while we were in the field.
Think: As stride increases, straddle should decrease. In other words, as I stretch out my steps, I would also be narrowing the width of my trail. Think of how an animal's trail looks in a walk compared to a run. A running animal can leave a trail that is only as wide as its tracks. Elbroch gives strides and straddles for a trotting bear as 27-37 inches long and only 6-10 inches wide. See what I mean? A bear's foot is about 5 inches wide, so a trotting bear is almost stepping in a straight line. But the results we obtained showed the opposite. The stride was elongated AND the width was increased. Visualize what the bears must do in order to use these trails. They are stretching their limbs farther than in a normal walk as well as placing their feet wider than they normally would. As I attempt this across my living room floor, I feel very uncomfortable and am reminded of a reptile rather than a mammal.
|FLCC Black Bear Management Class 2011|
(Paul's Ash Tree, 7/11)