Changes in marsupial herbivore densities in relation to a forestry 1080-poisoning operation

Abstract

Summary Tasmanian forestry companies commonly manage browsing damage to seedlings on plantations through the lethal control of native mammalian herbivores, using ‘1080’ (sodium monofluoroacetate). Although this practice is controversial, there is a lack of published quantitative data on its success in reducing animal numbers. We present the first published study quantifying the effects of a poisoning operation on the densities of mammalian herbivores both on a poisoned plantation and in the surrounding environment. Line transect surveys were used to monitor species densities before and after poisoning. The species targetted by the poisoning operation were the red-bellied pademelon (Thylogale billardierii), the red-necked wallaby (Macropus rufogriseus subspecies M. r. rufogriseus), the common brushtail possum (Trichosurus vulpecula) and European rabbit (Oryctolagus cuniculus). One non-target species, the common wombat (Vombatus ursinus), was also monitored. Poisoning significantly reduced pademelon density on the poisoned plantation (decline of 98%). A significant decrease in red-necked wallaby density was also detected at this time (decline of 60%) but a general declining trend was present within the data, so we interpret this result with caution. No significant effects were detected for possums, rabbits or wombats. The high kill-rate for pademelons may reflect the dominance of this species over others at bait stations and/or greater sensitivity to 1080. Six weeks after poisoning, the density of pademelons on the treated plantation had increased but was still significantly lower than before poisoning. At the same time, red-necked wallaby density on the treated plantation had increased, with animals moving onto the plantation from surrounding habitats. The decline of pademelons was hypothesized to enable an influx of red-necked wallabies onto the poisoned site, through reduced inter-specific dominance behaviour.