Effectiveness of bait tubes for brown treesnake control on Guam

A bait tube is a device with which a toxicant inserted in a dead mouse (Mus musculus) can be delivered to invasive brown treesnakes (Boiga irregularis) with low risk of non-target bait take. We tested two bait tube designs in a 5ha snake enclosure where the identity of virtually every snake is known. Instead of using toxicants, we implanted radio transmitters in small (6.6±1.4 g) and large (21.8±2.9 g) bait mice. Knowing all snakes present in the population allowed us to characterize not only covariates of snakes taking bait, but also those of snakes evading our mock control effort, and if snake covariates interacted with any design variable in determining targeting rate. Tube design had no effect on take rate. Snake snout-vent length was a strong predictor of success: none of the 29 snakes smaller than 843 mm took any bait, while the 126 snakes ≥843 mm were responsible for a total of 164 bait takes. The smallest of these snakes were able to ingest small and large mice, but tended to consume small bait at a higher rate than large bait. The main reason for our failure to target smallest snakes appears not to be gape limitation, but rather that small snakes prefer other prey (lizards). The time it takes a snake to grow from the size threshold observed to the size of maturation has implications for the interval between discrete efforts using toxic bait. Targeting all snakes before reproduction can occur is highly desirable; otherwise, a new cohort of refractory snakes may enter the population.