Track Casting
Making a cast is one of the time-honored ways of creating a permanent record of an animal track. Because of the ephemeral nature of tracks in the field, a track cast invites you to revisit tracks over and over again. The three-dimensional aspect of the cast allows for more in-depth analysis of foot morphology. Creating a track cast collection is a tangible way to increase your exposure to animal tracks when not in the field. Track casts are also great for teaching tracking in a classroom or workshop setting.
The simplest and most cost-effective medium to use is plaster of Paris. It pours easily and dries quickly in most weather conditions. Latex, dental mold, or paraffin are used less often but are also effective. The following tips are for making casts with plaster.?
The trail and burrowing mound made by a mole crab. Their trails are common at low tide in the intertidal zone.
MIXTURE In a suitable container (either a plastic cup or Ziploc bag), mix a ratio of about two parts plaster to one part water in a quantity to fill and cover your track. The consistency of the mixture is of greater importance than the exact ratio and should be thick like a milkshake. Thinner, more watery mixtures pick up better detail, but they are more fragile and may have a chalky consistency when dried. We would also recommend that you add the water slowly. You can always add more, but if you add too much, you must hope you have additional plaster in your pack to thicken your solution sufficiently to use.
POURING THE PLASTER Many tracks are delicate, and pouring plaster directly onto the track can damage them. It is a good idea to hold your mixing implement about an inch above the track to break the fall of the plaster, which will then gently fill the track. Once the plaster has been poured, it is a good idea to tap or shake the surface with your mixing implement to encourage any air bubbles to surface and break. This also helps move the plaster into the deepest cavities of the footprint, like the fine marks made by claws.
DRYING Well-mixed plaster on a hot day in the sun and on dry substrate can be dry enough for transport in less than 20 minutes. In cold, wet conditions it may take a few hours. The cast should be fully cured in 24 to 48 hours.
OTHER TIPS A barrier of some kind placed around the track to hold in the plaster can improve the appearance and thickness (strength) of the cast. You can easily make such barriers by cutting out strips from plastic containers of various sizes.
As soon as water is added to plaster, a chemical reaction occurs that releases a small amount of heat. This is problematic for snow conditions, because the plaster melts the snow and misshapes the cast. The solution is a product called SnowPrint Wax, which is a wax that can be sprayed into the track before pouring the plaster. This product prevents the snow from melting.
You may also come across a track preserved in silt mud or clay. You can carefully cut and lift out such a track and preserve it in a dry area. Unlike casting, this preservation technique provides a more pristine first generation of the track; even better, it is not subject to the variables of casting.
Whether you are casting or cutting a track out of substrate, be aware of your impact on the land. Also realize that casting is potentially messy and may involve toxic materials. Clear and concise procedures regarding setup and cleanup of casting are imperative.
Photography
Photographs are a quick way to record tracks and are an excellent tool for learning. Inexpensive digital point-and-shoot cameras are capable of taking decent-quality track photographs and can be carried in a shirt pocket. The drawback of a compact camera is the small sensor, which often equates to high noise levels in low-light situations (common when photographing tracks). High-quality digital single-lens reflex cameras can produce professional-quality images but are bulkier, more expensive, and require more experience and skill to use correctly. Regardless of which camera you choose to carry on your tracking expeditions, your photographs will become a powerful tool for learning and documenting your observations.
Cameras are also excellent tools for recording rare animals. Mark Elbroch snapped this photo with a cheap flip phone to record the tracks of a rare Wolverine atop Castle Peak in the northern Sierras.
Photographs allow you to analyze details that you may have overlooked in the field. By keeping your photos organized and labeled, you can compile a library of different species that you can revisit and compare with each other. You can also enlarge your photos and look for details you may have missed in the field.
Tips for the Field
FILL THE FRAME When taking an image of a single track, position the camera directly above the print and fill as much of the frame as possible. This may require being on your knees and elbows, but photos taken from a standing position rarely have enough detail.
STEADY THE CAMERA Supporting the camera on a tripod is the best method of track and sign photography, because a tripod allows you to use the necessary large F-stops to capture an entire image in focus even in shaded area or low-light conditions. It is possible to take good-quality images by hand when there is adequate light. If you are hand-holding a camera, it may help to stabilize your elbows against the ground or some other object. A general rule of thumb is to use the smallest aperture possible that allows you to use a shutter speed fast enough to avoid blur. Traditionally the slowest hand-holdable shutter speed is the numerical equivalent of the focal length of the lens. Thus, if you are using a 100-mm lens, never use a shutter speed slower than 1/100th of a second.
SHADE THE TRACK Unless the sun is at a very low angle (sunrise or sunset), it is preferable to shade the track. Direct, overhead sunlight removes contrast and may create shadows that distort the shape of the footprint.
Common Poorwill tracks in shade. The penny is ¾ in. (1.9 cm) in diameter and is a useful scale you might have in your pocket.
The deeper, darker impressions in the snow are the trail of a hunting Ermine tracking down a deer mouse that left the smaller, lighter tracks grouped in fours. Photo by Jonah Evans
USE A SCALE Try to place a ruler or other object of known size in the image. In some situations, the absence of a scale can make it much more difficult to identify the track. This is especially important when recording data and documenting the presence of a rare or controversial species.
TAKE SEVERAL IMAGES The great thing about digital cameras is that taking photos is free. Take several photos of each track and vary the shutter speed, aperture, zoom, and other camera settings. When you get home you can select the best image and delete the rest. Taking a few extra photos is well worth the effort when compared to the disappointment of finding that the one photo of a track you took is blurry.
Carnivore Scent Stations
Carnivore scent stations are a fancy name for a human-made track trap. Scent stations were developed by researchers to attempt to maintain a probability of detecting an animal across locations, time, or both. One of the challenges of using tracks in research is that substrates vary, and it is easier to find tracks in some areas than in others. Thus, if few tracks are recorded in an area, this might mean that few animals inhabit the area, or it might be a result of poor tracking conditions.
Scent stations include a scent lure and either an artificial tracking surface such as sand or gypsum, or an enhanced surface obtained by raking an area or sifting local soils. Researchers place scent stations across a landscape and use visitation rates of different species to estimate a variety of parameters including relative and actual abundances. See Long et al. (2008) for a detailed presentation of methods and scientific designs using both scent stations and prepared tracking substrates without baits.