Endangered Species Recovery Program

An animal track casting method using dolomite, sand, and spray adhesive

California Department of Fish and Game 85:138-139 (1999).

Howard O. Clark, Jr.
Endangered Species Recovery Program
Fresno, California

Recording and preserving tracks are good ways to document the presence of species. Various methods have been developed to measure tracks, and plaster is the most common of the methods (e.g., Aiken 1930). Occasionally, a natural mud mold can be cut out and saved (Murie 1954). Other methods include paraffin wax (Murie 1954), wood putty (Halfpenny 1986), and rosin-paraffin (Kent et al. 1985). Halfpenny (1986) also conducted casting experiments with spray insulation foam with moderate success. Success with paraffin has been limited (Kent et al. 1985), and plaster casts are fragile and bulky to store (Halfpenny 1986).

Carbon-sooted aluminum track plates are the most widely accepted method of track preservation being used today. Transparent tape is used to lift and preserve tracks off of aluminum plates (Orloff et al. 1993). Animal tracks left on carbon-sooted aluminum track plates are highly detailed and identifying the species is much easier than traditional casting methods (Taylor and Raphael 1988, Orloff et al. 1993, Zielinski and Truex 1995). However, carbon-sooted aluminum track plates are bulky and inconvenient to prepare for use, even if the aluminum plates are chalked instead of sooted. Moreover, research locations near urban settings or busy roadways are subject to vandalism. Aluminum track plates may attract the attention of passers-by and may be tampered with. Because of this, these research areas are not always suitable for aluminum track plates. In such circumstances casting in a mineral track medium is an appropriate alternative.

To evaluate an alternative to these methods of documenting tracks, I placed a tray, measuring 122 cm x 45 cm x 5 cm, in an open area and filled it with a 50/50 mixture of dolomite. I smoothed the track medium surface using a hand-held cement float. Domestic cats were allowed to walk across the medium, leaving behind a variety of tracks. I selected a suitable track and sprayed it with fast-drying polyurethane (a clear spray varnish used to place a high gloss finish on wood products) from a distance of 30 cm, moving the spray can back and forth, not allowing the spray to soak the track. The track was frozen in place with polyurethane to prevent distortion. Once the polyurethane dried, I sprayed 3M spray adhesive (an adhesive used to bond materials together) on the track. I initially moved the spray adhesive can from side to side, spraying in short bursts until a thin film completely covered the track. Once the film formed, spraying was not likely to distort the track and I continually sprayed until the track concavity was filled with adhesive.

I also made plaster casts (Smith 1982) in the dolomite/sand mixture as a comparison casting method. I collected 30 spray adhesive casts and compared them to 30 plaster casts made under the same conditions. Both methods exhibited good 3-dimensional detail, emphasizing track form and size. Plaster casts could be lifted within an hour, but the spray adhesive casts could not be lifted for 3 to 4 hours in hot weather (~38^oC). At 4 hours, the spray adhesive tracks were still soft and could be distorted with excessive handling. A 12-hour curing time was required to ensure a firm cast. In both methods, sand particles attaching to the casts affected quality of detail.

Three advantages of making spray adhesive casts over plaster casts were evident: 1) less storage space was needed, 2) a reduced carrying load for field casting, and 3) less time spent preparing and making casts. Spray adhesive casts are relatively flat (no thicker than 5 mm for cat tracks at the concavity) and fit nicely in an envelope. Alternatively, plaster casts are comparatively thick (average thickness of 15 mm for cat tracks), require more storage space, and are fragile. Casting materials in the field for the spray adhesive method amounted to 2 spray cans: 1 polyurethane and 1 spray adhesive. Plaster casting requires carrying a container of plaster powder, a mixing can, a container of water, and a mixing stick. Additionally, clean up is time consuming. The spray adhesive method only takes about a minute to execute, while the plaster method can take up to several minutes.

Casts made by both methods are comparable in detail, but plaster appears to show markedly more detail because fewer sand particles attach to the plaster. Sand particles readily attached to the cast surface using the spray adhesive method. The sand particles, however, did not distort the track, and the track was clearly visible.

Although carbon-sooted aluminum tracking stations are a widely accepted method, they cannot be used under all circumstances. Depending on the research objective and local factors, other tracking methods may be better suited. The dolomite, sand, and spray adhesive method, a variation on the casting theme, is one solution.