This article is part of
Wilderness Way
VOLUME 13, ISSUE 4.
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Measuring Animal Tracks: How and Why
by Jim Lowery
Before there were tape measures and rulers, there were fine trackers who could interpret and follow tracks with a precision we might envy. So why should we modern people bother to measure animal tracks?
Consider it an investment in learning for those of us who do not spend every moment of our lives observing nature around us. Measuring is one of those tools that helps identify tracks, tell age and gender, and teach about animal behavior and biology. After nearly twenty-five years of intensive tracking, I can "eyeball" many tracks to tell a lot about the animal that made them. But I still use measurements to refine and to learn more.
Measuring for Track ID
Measuring the width and length of clear prints is the
obvious starting point. Track lengths should not include
claw marks if there are any, because many times claws do not
show. The most common measurement I take is the hind track
width. This is because for many mammals such as hoofed
animals, cats and dogs, the front track is covered by the
hind track in a walk anyway. Also, track length can be
harder to measure, because the moving foot can obscure the
leading or trailing edge of the track. But measure all you
can.
Be sure to measure the size of the foot that made the track, not the distortions from soil movement and collapse.
Photo 1 shows a coyote hind track in dry sand, with the
horizontal line showing the true width of the track; the
sand collapsed to make the track look 50% larger than it
really is. With a diagonal walking trail (for example, deer,
fox or bobcat), make sure you measure the hind track within
the front one underneath it. Otherwise you will overestimate
the size of the track. Photo 2 illustrates how to
measure the hind width of a gray fox track that is
superimposed over the front track.
What do you do with these measurements? Compare them to field references and to your own notebooks. My Tracker's Field Guide has averages and usual ranges, based on thousands of field measurements. (Ideally you will want ranges, not just examples or averages.) Other references with good track range data are Mark Elbroch's Mammal Tracks and Sign, and Paul Rezendes' Tracking and the Art of Seeing. Tom Brown, Jr.'s Field Guide to Nature Observation and Tracking has good averages (but not ranges) as does Jim Halfpenny's Mammal Tracking in Western North America. The otherwise good Peterson Field Guide to Animal Tracks has only track measurement examples, and is therefore not very useful.
Let us say you find a dog family track and from the habitat
you have narrowed it down to gray fox or coyote. As Photo
3 shows (all of whose tracks are depicted proportional
to their average sizes), a fox track on the average is quite
a bit smaller than a coyote's, and measurements would
confirm the ID most of the time. When you would find an
overlap would be with coyote pups, and indeed I have seen
such a thing about twenty times. Though helpful,
measurements are not always the final answer.
If your track falls outside of the range given in your field guide, ask these questions: Have the toes spread due to the soil, e.g. soft mud, to create a distorted track? Have I found an unusually large member of the species? Or should I rethink my track ID? Number three is the most likely option, by the way.
The cat tracks in Photo 3, in my experience, would almost never overlap in size. Even the smallest mountain lion cub track I have ever seen is still 3/8-inch wider than the largest bobcat track I have measured. Cougar mothers keep their tiny ones really hidden, so while it is possible, it is very unlikely that you will ever see a mountain lion kitten's track in the wild that is as small as a bobcat's.
The hoofed animal tracks in Photo 3 show a mix. I have found that mule deer and bighorn sheep tracks overlap in size a whole lot; the hind track width for either could most often range from 1-1/2 inches to 2 inches. So, you will have to use other clues including the shape of the track and the habitat. However between deer and elk, measuring will nail the ID almost every time. A small juvenile elk will leave tracks with the same size and stride as an adult mule deer, but these tracks will likely not be far from the mother's.
Speaking of stride, use this measurement to help track ID for mammals which normally create a diagonal walking (alternating) track pattern or a pace (overstep) pattern. (These would be hoofed animals, cats, dogs, opossums, badgers, bears, skunks, porcupines, and woodchucks for example.) This is because the stride, measured from the toe of a hind track to the toe of the opposite hind track, will be proportional to the animal's shoulder-to-hip length, and you can visualize how big your animal is. Make sure your animal is walking, not trotting so that the stride measurement can be compared to what is in your field guide.
Going back to the deer vs. elk tracks, I have found that
mule deer walking strides in my area rarely exceed 23
inches, while elk strides are rarely less than 22-1/2
inches. Photo 4 shows how to measure the stride of a
diagonal-walking opossum; the left and right strides will
usually be slightly different.
For the other mammals that typically
gallop or bound (rabbits, many weasel family members and
most of the rodents), stride does not help very much
because it can vary so much with speed. For these, measure
the trail width instead, which is
proportional to the animal's body width. Photo 5
shows how to measure trail width using a woodrat as an
example.
For example, I find a galloping track pattern (groups of four tracks with the hind ones landing past the front ones as in Photo 5), and the trail width is four inches. In my area, the only possibilities would be black-tailed jackrabbit, cottontail, western gray squirrel, or the introduced fox squirrel. The size and shape of the tracks themselves, the number of toes etc. should normally give me the answer.
Measuring for Gender and Age
For many mammal species, the adult male is larger than the
female and the tracks will correspond. However, gender can
usually be determined reliably only when you find tracks
that are especially large, indicating a big male;
medium-sized tracks could belong to an adult female or a
sub-adult male. You are going to have to learn from field
guides which of your local species have a pronounced size
difference between male and female. Bears and many hoofed
animals, along with weasel family members like mink, weasel,
and marten, will show the mature male significantly larger
than a female. But among others like gray fox and raccoon,
males are only 10% to 15% larger than females on average, so
there will be much overlap in track size.
You can make an educated guess when you find tracks of a mated pair traveling together, for example coyote or fox; the larger tracks would belong to the male. Remember to read up on the social behavior of your animal though; some mating pairs travel together only for a short time each year, while others travel together throughout the year.
Photos 6 and 7 show tracks of a mother black bear and her cub, and a mother elk and her calf. Measuring such tracks when you have the opportunity is essential to understand your local animals. You not only learn the size of a juvenile's track, you also know that the adult tracks alongside must be the female, giving you good baseline measurements. You also know that the female black bear is probably at least 5 years old, because bears normally reach breeding age at 4-1/2 years. The elk calf shown in Photo 7 was only a few days old, incidentally.
Last June I came across tracks of three black bears traveling together. The largest one's hind track measured 6-1/2 inches wide, and the other two measured 5-1/2 inches and 5 inches respectively. These bears gave me some excellent information, because the "5-inch bear" walked under a fallen log with a clearance of 26 inches beneath it, while the other two bears walked around the log. So I could get a picture of how tall the smallest bear was, and I also got measurements of an adult female's tracks. The small bears were probably yearlings; I am guessing a male and a female.
A few years ago I took the opportunity to measure a captive mountain lion's tracks. At 7-1/2 months old, Dylan, born in captivity, had a left hind track that measured 3-1/4 inches wide by 3-9/16 inches long, and a walking stride of 17 inches. A year and a half later, pretty much full grown, his left hind track had grown to 4 by 4-1/4 inches and his stride to 21-3/8 inches. That gave me an idea about a cougar's growth rate (albeit with a top-of-the-line diet in captivity).
Measuring Tracks for
Individuality
Careful track measurements can reveal details about
individuals in a local population. Left and right strides,
trail width, straddle and pitch (the inward or outward
orientation of a track related to the direction of travel),
will all help you identify individual animals. This will be
a subject we will dwell on further at another time. For
instance, two raccoon trails clearly show differences in
placement of the front/hind, and left/right tracks.
Measuring the right and left strides of the two animals
clearly records the differences. You may notice that one
raccoon shows a significant straddle (space between the
tracks) between the left front and right hind tracks.
Individuality is pretty easy to tell from raccoon tracks.
For other species it is more subtle but the method is the
same.
So throw a tape measure, a pen, and
a small notebook in your day pack and start to understand
your local wildlife!
