Field Guide to Animal Tracks and Scat of California. Lawrence Mark Elbroch
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Название: Field Guide to Animal Tracks and Scat of California
Автор: Lawrence Mark Elbroch
Издательство: Ingram
Жанр: Биология
Серия: California Natural History Guides
isbn: 9780520951648
isbn:
A portrait of a Desert Kangaroo Rat hiding in cover in the Mojave National Preserve in southern California.
Each of the three speed categories is associated with some general interpretations. The key to applying this to some animal you are tracking is in knowing what is their normal gait and associated natural rhythm. You can acquire this knowledge through experience in the field, watching animals in videos, or reading guides to tracking and animal behavior. As described above, the normal gait for Bobcats and Cougars is a walk, but the normal gait for Coyotes and foxes is a trot. The normal gait for squirrels is a bound, and for kangaroo rats, a bipedal hop.
Consider the Desert Kangaroo Rat (Dipodymys deserti), an animal the authors have never seen use any but three gaits and speeds: slow, normal, and fast. When moving slowly, Desert Kangaroo Rats bound on all four feet, like a squirrel, and they drag their tail on the ground behind them. They move in this way when they are foraging and scent marking, or when they are exploring the scents of other kangaroo rats. The normal gait of Desert Kangaroo Rats is a bipedal hop, which they use to travel between their burrows, foraging areas, and areas where they leave territorial scent marks. The bipedal hop is generally a sign of comfort and that everything is normal. Desert Kangaroo Rats skip to evade predators (it is a sign of fear) and in territorial chases with other kangaroo rats, including the courtship rituals that precede mating. Thus, we have three clear categories of movement, three speed categories, and three distinct categories of behavior associated with these gaits and track patterns. This of course can be done for any and every animal you follow.
In mammals that use more than three gaits, consider dividing each of the three categories into three; thus, you have nine potential speeds and interpretations. For example, Mountain Lions (or Cougars) use an overstep walk, or amble, as their normal gait. They speed up into a trot when exposed and crossing open ground, traveling to a known destination with some agenda in mind, and when confronting conspecifics in territorial encounters (stiff-legged trots communicate dominance in many mammals). They gallop when pursuing prey or startled, and lope when slowing down when they recognize that an initial threat is not as dangerous as they first thought, or is remaining stationary—three versions of “fast,” each with different potential interpretations. But start with just three categories, and then add more as you feel more comfortable with the basics.
Bounding trails with tail drag of slowly moving Desert Kangaroo rats.
Rapid skips of an evading Desert Kangaroo Rat.
The beautiful trail of a large black bear sloshing in an overstep walk up a muddy riverbed in the Los Padres National Forest in southern California. Killdeer trails cross in the forefront of the photo.
The Effects of Substrate on Gaits
Let us use ourselves as models. Compare the trails you leave while walking in an inch of snow and two feet of snow, or on firm ground and in deep, dry sand if you live in arid regions. It is likely that the length between your tracks decreases in deeper snow (softer, deeper sand) and that the width of the entire trail pattern increases. This is a wonderful lesson in the effects of the depth of substrate upon trail characteristics. Now, let's add another variable: speed.
In deep snow a black bear is forced to use a direct-register walk, as seen here in this bear switching dens in the middle of winter near Tahoe. Compare this trail to that on page 67, where a bear moves in shallow mud.
When looking at trail characteristics in relation to depth of substrate, it may be more accurate to discuss energy output rather than speed. Let us return to our two trails in snow. If you were to use the same amount of energy in each trail, you would move more slowly in the deeper conditions. Moving at the same speed in both trails would require a higher degree of energy output to maintain that speed in two feet of snow. Consider running in the two snow conditions. Could you run at the same speed in two feet of snow as in an inch of snow? Would the energy output be equivalent while maintaining a run in these two very different conditions?
Just as we adapt to changing conditions, so do other animals. In fact, as you track across varied substrates, you will begin to note that animals change the way they are moving in ways that reflect an awareness of energy efficiency. Trotting in deep snow is intensively difficult, if not impossible at times, and so Coyotes are often found walking or bounding for short distances in these conditions. Fishers, which tend toward a 3 × 4, or rotary lope, change tendencies to a 2 × 2 or transverse lope in deep, soft conditions, and often walk longer distances as well.
Tracking in Snow
Snow tracking varies from a simple exercise in perfect track identification to incredibly difficult interpretations of deep, windblown trails. Below are some techniques and approaches useful when interpreting tracks and trails in snow:
TRACK PATTERNS. Learn to rely more on track pattern identification than print identification, and in this way be able to identify species from greater distances and through binoculars. In open areas of the North, biologists complete track transects of far-ranging mammal species, such as Wolverines, by small plane.
GAIT CHANGES. Be aware of the gait changes animals make when moving in snow. Animals that do not typically direct-register walk suddenly begin to do so. As an example, consider the raccoon, which uses a distinctive 2 × 2 walking gait in shallow substrates. But in snow, raccoons use a direct-register walk. Also mammals that tend to trot or lope in shallow substrates, walk more frequently in deep snow. Remember that the depth of substrate is one of the key variables in determining how an animal moves.
DETERMINING DIRECTION. The direction of travel in a given trail can be determined by identifying the deepest part of an individual track (the deep end points forward), but check several tracks to be sure. Place your hand into trails filled with snow to feel the direction of travel. This is best done without gloves, so be prepared and be conscious of conditions.
TOUCHING TRACKS. Feeling snowed-in tracks offers more than the direction of travel. The mound in the center of canine tracks can often be clearly felt, or the ridge between palm and toe pads in a cat track, or hooves. You'll also be able to tell the approximate size of the track, and how flat the floor of the track is. For example, the floor of canid tracks in deep snow is significantly steeper than the floor of tracks made by felids.
Feel snowed-in tracks very gently without gloves. The area compressed by the animal will always be firmer than the snow that has blown or fallen in. Use the body heat of your hands to melt out tracks; in this way you can sometimes not only feel the track but recreate it visually. However, do not force fingers into spots too quickly so as to create the track you want; carefully and slowly melt out the existing track floor.
BLOWING OUT SNOW. When light snow has filled in a set of tracks, you can often blow them out and keep the track intact. This is an especially useful technique when temperatures are cold and a fresh, light layer of snow has covered tracks.
CLAWS. Look for the placement of claws in snow tracks. In deep snow, all that may be clear in Coyote tracks are the pinprick claw marks of toes 3 and 4 at the very end of the track; you may have to squat to see them. Tracks of Bobcats and other cats may be differentiated from canine tracks by looking for claws that register СКАЧАТЬ