Effectiveness of aerial baiting of possums in different seasons and different forest types (original) (raw)

The use of different types of toxic bait for sustained control of possums

Proceedings of the New Zealand Plant Protection Conference

Assessment of six types of toxic bait in replicated field trials demonstrated that baits containing 0.15% 1080 were the most costeffective for initial control of possum populations. Possums surviving an initial exposure to either 1080, cyanide, or cholecalciferol baits would not eat lethal amounts of bait containing another fast-acting toxicant during the following 2.5 months. However, 'shyness' to 1080 or cholecalciferol baits in possums surviving initial control was overcome by using a slowacting anticoagulant poison during maintenance control. Sustained control of possums is currently most cost-effective if baits containing 0.15% 1080 are followed at least 2 months later by baits containing 0.002% brodifacoum. Unlicenced operators can similarly achieve sustained control of possums at very low densities by using brodifacoum baits 2 months after initial control is undertaken with baits containing cholecalciferol.

Possum monitoring using raised leg-hold traps

2000

Science for Conservation presents the results of investigations by DOC staff, and by contracted science providers outside the Department of Conservation. Publications in this series are internally and externally peer reviewed.

Evaluation of Non-Toxic Bait Interference for Indexing Brushtail Possum Density

Percentage non-toxic bait interference is currently used by local authorities to monitor brushtail possum control operations but the validity of the method has not been established. Two models have been proposed to estimate an index of possum density (possums per bait) from a log-transformation of percentage bait interference. In two trials, percentage bait interference and the density index derived from percentage bait interference using the Bamford (1970) model usually increased from night to night. Variation in the number of possums per bait was reduced by dividing the Bamford index by the number of nights baits were put out, as proposed by Jane (1981). The spatial distribution of bait interference along lines of bait stations was random for the first night and usually for at least 5 nights. Rhodomine dye and cyanide poison, alternated at bait stations after at least 5 nights non-toxic baiting, showed that about 83% of possums in one trial and 29% of possums in the other trial interfered with more than one bait on the same night. Increasing the spacing between bait stations reduced the proportion of possums interfering with more than one bait. The number of possums per line killed by cyanide baits after at least 5 nights of non-toxic baiting was strongly correlated with percentage bait interference, with and without logarithmic transformation, on the first night. The possums' apparent ability to remember the location of bait stations from one night to the next means that, in the absence of better advice, the original Bamford (1970) model should be modified as proposed by Jane (1981) to estimate possum density and change in possum density (e.g., from pre-to post-poison).