Sustained recall of bait acceptability in captive brushtail possums (Trichosurus vulpecula)

Abstract

Non-toxic prefeeding is often used to increase the efficacy of aerial poisoning of possums (Trichosurus vulpecula) by increasing their willingness to accept toxic bait. An important question is whether that increased acceptance lasts more than a few days or weeks– if not, repeated prefeeding might be required if the poisoning was delayed by poor weather. We presented 48 captive possums with 100 g of non–toxic bait for 40 min on three or more occasions at a range of intervals (1–28 days), and measured bait consumption on each occasion. Bait consumption increased from a mean (±SE) of 23.3 ± 2.5 g on first encounter to 32.9 ± 2.4 g on the second encounter, but without further increase on the third encounter (32.7 ± 2.5 g). The amount of bait eaten increased (rather than decreased) as the time between exposures increased. When possums were subsequently offered toxic bait (sodium monofluoroacetate) at a range of intervals (10–50 days) after their last exposure to prefeed, there was no evidence that amount of toxic bait consumed declined as the time since last exposure to non-toxic prefeed increased (r = −0.23, d.f. = 45, P = 0.085). The results indicate that a single short period (40 min) of exposure to prefeed should be sufficient to induce a sustained willingness to accept bait that lasts at least 1 month.