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Not long ago we developed a convenient, inexpensive, non-harmful way to learn about the secret lives of small nocturnal mammals. The technique allows us to follow trails made by rodents and to find where they have foraged, what they have eaten, and where they have their burrows. This method involves the use of a fine, nontoxic powder that fluoresces under black light. After setting traps and capturing the animals alive, we gently dust them in the fluorescent powder. The powder, used to make fluorescent paint, comes in different colors. It is especially important that the powder is non-toxic because killing the animals or hurting them in any way would be detrimental to any community, populational, or behavioral study. These pigments have been used in feeding experiments and our experience has been that the animals that are dusted suffer no ill effects either from the powder or from predation because of a change in visibility of them as prey items.
Once the powder is applied and the rodent goes on its way, we can follow its trail with a black light. The powder is very fine and rubs off a little at a time as the animal brushes past grass stems or other parts of plants. When the powder is illuminated with ultraviolet light a brightly fluorescing trail is left to reveal where the animal has traveled.
The trail is surprisingly revealing. If the animal climbs a tree, a trail is made on the bark; if it goes into its hole there is a brightly colored ring at the entrance; if it climbs to the top of a sunflower plant to eat the fruiting head, the fluorescent husks and leavings are found near the fluorescing stalk. If the animal does a little sand-bathing, it leaves a fluorescent sandy patch that is easily spotted. If an animal of one color follows an animal of a different color down the same path, the order of which came first is easily determined.