Scent-Station Visits as an Index to Abundance of Raccoons: An Experimental Manipulation

We tested the premise that rates of visitation by raccoons (Procyon lotor) to scent stations vary directly with population density by manipulating the density of an island population of this carnivore in middle Tennessee. Despite its widespread use, the scent-station index to population size has not been validated. General protocol for scent stations followed previous investigators; radiotelemetry was used to monitor individual behavior of raccoons. We determined minimum population size from the records of known captures and compared them with visits to scent stations recorded twice monthly during an initial period with no manipulation (May 1987–August 1988); similar procedures were used during an experimental period (September 1988–August 1989) when raccoons were removed and held on the mainland for ca. 1 month during each season and then returned to the island. Abundance of raccoons on the island ranged from 32 to 42 when estimated twice each month; computed indices of relative abundance varied from zero to 286. Rates of visitation by raccoons were highest in spring and summer during both the baseline and experimental period. Visits to scent stations were independent of density throughout the study. During the experimental period, both the largest and smallest observed indices of relative abundance occurred when an estimated 25% of the population had been removed and when all known animals (n = 40) occurred on the island. Local fluctuations of populations may precipitate changes in behavior of raccoons that preclude the use of scent stations to index abundance, particularly in heterogeneous habitats.