Dye Excretion as a Method for Determination of Small Mammal Home Ranges

One hundred and twenty dyes and biological stains were tested in the laboratory for possible use in determining home ranges by excreted dyes. Dyes were mixed with beeswax, made into pellet form, and placed subcutancously in Mus musculus and Microtus ochrogaster. Nine dyes colored the urine for four or more days (using 60-95 mg pellet) and did not depress activity as measured by activity wheels. In field tests, dropping boards covered with filter paper were placed in a grid for recovery of colored urine from M. ochrogaster implanted with pellets. Home ranges calculated from the excreted dye spots corre- sponded closely to home ranges calculated from live trapping data for the same animals (using minimum area method). Dyes in the same color range were found to be usable on different animals in the same area if one changed color when drops of weak acid or base solution were placed on the spots. Most techniques designed to determine the home ranges of small mammals utilize some type of live trapping and recapture procedure. Many criticisms have been leveled against this method (Davis, 1953) but no clearly superior technique has replaced it. The purpose of this study was first to develop a new method for determining home ranges which would eliminate some of the objec- tionable features of live trapping studies. The procedure developed was to implant pellets of dye into animals and determine movement by recording colored urine spots on dropping boards (Emlen et al., 1957). Secondly the home ranges of some individuals were determined by conventional live trapping methods and then by the new technique to compare results obtained by these methods. MATERIALS AND METHODS LABORATORY Initially 120 dyes were screened to determine their usefulness. Each dye was separately tested by preparing a pellet composed of a 1: 1 ratio of dye to beeswax. Beeswax was used to form a matrix which prevented crumbling, and also slowed and prolonged absorption of dye from the pellet. Homogeneous mixing of dye and beeswax was accomplished by placing the weighed mixture of beeswax and dye granules in a paraffin oven at 560 C until the beeswax melted. This semi-liquid mixture was then removed from the oven and stirred with a glass rod until it hardened. The quantity of dye-beeswax prepa- ration desired for a pellet was weighed in milligrams on a Roller- Smith torsion balance and then placed in a glaze-finished crucible for pulverization by a pestle.