TIME-SPECIFIC TRACER TO INDICATE BAIT ACCEPTANCE BY SMALL MAMMALS

Tests were conducted to find a tracer that would indicate whether small mammals had eaten treated bait within a 24-hour period. A nontoxic acid-base indicator, Bromcresol Green (3,3', 5,5'-tetrabromo-m-cresolsulfonephthalein) was satisfactory. In the laboratory, grain treated with Brom- cresol Green was well accepted by Peromyscus maniculatus, Microtus ochrogaster, and M. pennsylvani- cus; predictable areas of the animals' gastrointestinal tracts were colored by the tracer during the first 18 hours after ingestion but were devoid of color by 24 hours. In the field, acceptance of dye-treated bait by 729 animals of five species ranged from 88.5 percent on the 3rd day after baiting to 43.8 per- cent on the 11th day. The apparent decline in acceptance may have been due to fading of the tracer or to a decrease in palatability of the bait. Decomposition of Bromcresol Green on grain from weather- ing was found to be delayed by overcoating it with Uvinul 490,2 an ultraviolet filter. TIME-SPECIFIC TRACER TO INDICATE BAIT ACCEPTANCE BY SMALL MAMMALS ROGER D. NASS, Bureau of Sport Fisheries and Wildlife, Denver, Colorado1 GLENN A. HOOD, Bureau of Sport Fisheries and Wildlife, Denver, Colorado1 Abstract: Tests were conducted to find a tracer that would indicate whether small mammals had eaten treated bait within a 24-hour period. A nontoxic acid-base indicator, Bromcresol Green (3,3', 5,5'-tetrabromo-m-cresolsulfonephthalein) was satisfactory. In the laboratory, grain treated with Brom- cresol Green was well accepted by Peromyscus maniculatus, Microtus ochrogaster, and M. pennsylvani- cus; predictable areas of the animals' gastrointestinal tracts were colored by the tracer during the first 18 hours after ingestion but were devoid of color by 24 hours. In the field, acceptance of dye-treated bait by 729 animals of five species ranged from 88.5 percent on the 3rd day after baiting to 43.8 per- cent on the 11th day. The apparent decline in acceptance may have been due to fading of the tracer or to a decrease in palatability of the bait. Decomposition of Bromcresol Green on grain from weather- ing was found to be delayed by overcoating it with Uvinul 490,2 an ultraviolet filter.