The USDA APHIS WS Unified Model for Estimating DRC-1339 Bait Application Take Estimates as Effected by French Fry Bait Size

DRC-1339 (CPTH, 3-chloro-p-tolouidine) is an avicide registered to reduce local populations of selected bird species at feedlots, dairies, and staging areas near rice fields, and to prevent livestock depredation. Additionally, two registrations are specifically for controlling gulls and pigeons. U.S. Department of Agriculture Wildlife Services personnel historically have used a variety of methods to estimate take, including counting carcasses and quantifying reduction in bird activity. Because this avicide is slow-acting and birds usually succumb away from the bait site, carcass recovery provides poor estimates of take. Because of natural variability in bird numbers and activity, quantifying reductions in bird activity is also a poor gauge of efficacy. Scientists at the U.S. Department of Agriculture APHIS Wildlife Services National Wildlife Research Center developed and continue to adapt and refine a model using a bioenergetics approach to estimate consumption and the resulting mortality from DRC-1339 bait consumption. The model estimates take for the major baits used under the feedlot and staging area labels for European starlings, blackbirds, brown-headed cowbirds, and common grackles. Consumption of homogeneous baits (rice, cracked corn, fat pellets) has been well characterized, and take (i.e., mortality) is accurately predicted in the model. However, predictions of take when french fries were used as a bait for controlling starlings at feedlots in Washington State were less accurate. Thus, we modified the model to capture the feeding behavior of birds using this highly heterogeneous bait by removing the dependence on bait mass and simplifying the calculation of dose ingested. The modified model calculates dose directly from the amount of DRC-1339 per calorie consumed instead of from the DRC-1339 concentration per bait consumed. In this paper, we compare estimates of take based on french fry bait mass distributions and caloric contents determined for five different french fry bait types