Identification of Mammal Tracks from Sooted Track Stations in the Pacific Northwest

1. What they did

Wildlife biologists often survey mammals with baited stations where animals leave tracks in fine soil or snow. That does not work well where soils are rocky. An alternative is a sheet of aluminum blackened with soot: an animal walking across it lifts the soot and leaves a print. The authors used such stations to study where medium and large mammals live in Douglas-fir forests of northwestern California, and found that the prints looked very different from those in field guides.

• The stations. Each station was two aluminum sheets (814 by 407 mm) coated with a thin layer of kerosene soot, baited in the centre with a can of tuna pet food.
• The survey. They checked 135 stations in 1981 and 166 stations in 1982 and 1983, each for 8 days between 1 July and 15 September, in the Klamath Mountains.
• Collecting the tracks. Tracks were lifted in the field by pressing transparent tape over them and sticking the tape onto a white data sheet. Up to seven measurements were taken on each track, keeping fore and hind feet apart.
• The key. From tracks of 23 species, they put together a standard way to measure tracks (Figure 1), a table of measurements (Table 1), drawings of each species’ tracks (Figures 2 to 5) and a key to tell them apart.

2. What they found

Tracks on soot are different

Prints on the hard, sooted surface were much smaller and far more detailed than prints in soil or snow. The measurements and drawings in available field guides were useless for identifying them.

The seven measurements

A: length from the front of the foremost toe to the back of the palm pad; B: widest spread of the toes; C: height of the palm pads; D: width of the palm pads; E: length from the foremost toe to the back of the heel pad; F: length from the foremost toe to the end of the heel mark; G: length from the foremost claw to the back of the palm pad.

The key, in three groups

• Four toes on fore and hind feet. Dogs (coyote and gray fox) and cats (cougar and bobcat). Dog tracks are oval, with toes about half the size of the palm pad. Cat tracks are round, the palm pad is larger in relation to the toes (toes about a third of its size), and claws do not show. The coyote track is over 40 mm long and wide with claw marks; the gray fox track is small with no claw marks. The cougar track is over 60 mm; the bobcat track is about 38 mm, with rounded, protruding lobes at the back of the palm pad.
• Four toes on the fore foot, five on the hind foot. Six squirrels and the dusky-footed woodrat. Squirrel fore tracks show four toe pads, three palm pads and two heel pads; hind tracks show five toes and four palm pads in an arc. The species are told apart by size and by the shape and arrangement of the pads. The western gray squirrel has the largest track and is the only squirrel that may show a long narrow extra heel pad. The woodrat’s toes leave a distinct figure-eight pattern. Chipmunk species could not be told apart and need to be confirmed by trapping.
• Five toes on fore and hind feet. Opossum, porcupine, black bear, ringtail, raccoon, fisher, marten, the three weasels (mink, long-tailed weasel and ermine), and the two skunks. The opossum’s hind foot has a widely separated first toe; the porcupine leaves large oval palm pads with a pebbled texture and toes rarely show; the black bear leaves the largest track. A male marten’s track may overlap in size with a female fisher’s; marten tracks are generally hairier and their palm pads show as three distinct pads. Mink, long-tailed weasel and ermine tracks have the same pattern and may overlap in size. Striped skunk claws always leave scratch marks well past the toes.

Sample sizes

The number of tracks measured varied widely: for example, 63 fore tracks of Douglas’ squirrel and 56 of black bear, but only one coyote track and two each of cougar and bobcat.

3. What they concluded

• Because more and more researchers were using sooted track stations, the technique needed to be standardized. The authors offer their measuring method and key as that standard for medium to large mammals in the Pacific Northwest.
• The list of species is incomplete, because the fieldwork was limited to forests in northwestern California. They recommend that further tracks and measurements be made available as they are identified.

4. How tracking was or was not used

The whole paper is about tracks and signs identification: identifying mammals from footprints left on sooted aluminum plates, using toe counts, pad shapes and track measurements. No trailing was involved. The paper does not say how the species that left each track were confirmed when the key was built.

5. Tracker or observer certification

Not reported. The paper thanks eight people for collecting field data and three for providing additional measurements, but says nothing about who identified the tracks or how their identifications were checked. This matters because the key and measurements depend on those identifications being right.

6. Other technologies, skills or innovations

• Sooted aluminum track plates, building on earlier work with sooted surfaces for small mammals and on Barrett (1983), who used them for martens and other carnivores in the Sierra Nevada.
• Preserving tracks by lifting them with transparent tape onto white data sheets, so they can be measured and kept.
• A standard set of seven track measurements for hard-surface tracks.