Estimating the Effects of DRC-1339 Treated Egg Baits on Common Ravens Using a Bioenergetics Model

Abstract

Author(s): Taylor, Jimmy D.; Stahl, Randal S. | Abstract: Depredation by common ravens often exceeds stakeholders’ levels of acceptance. Common sources of excessive raven damage include loss of young livestock and nest depredation of species of concern, such as desert tortoise, greater sage-grouse, and least tern. USDA/APHIS Wildlife Services applies the avicide DRC-1339 (3-chloro-p-toluidine hydrochloride, CPTH) formulated in an intact-boiled egg bait to reduce such damage under the DRC-1339 Concentrate Livestock, Nest a Fodder Depredations label (EPA No. 56228-29). Although considered extremely effective on corvids, DRC-1339 is a slow acting toxicant and ravens may succumb away from the bait site, preventing the use of carcass recovery as a means to estimate take. To estimate take, Wildlife Services employs a model comprised of a bioenergetics module to predict consumption combined with a toxicological module that predicts mortality based on a probit analysis. This model has recently been revised to improve and standardize take estimates for common raven management activities using the egg baits covered by this label. Common ravens exhibit complex behaviors that impact the amount of bait consumed when offered DRC-1339 egg baits. The approaches to capturing this behavior in the model are presented along with take estimates associated with a range of baiting scenarios.