Non-Toxic Bait Interference

A non-toxic bait interference method is being used in the Haupiri research area to establish the relative levels of pasture utilisation at increasing intervals from the main bush margin.

Monthly samples consist of lines, 100 m apart, which run from 250 m inside the bush to a maximum of 850 m into pasture. Bait stations consist of a small length of alkathene pipe attached to a reinforcing rod, into which is forced a plastic cap to contain the bait. These are placed at 50 m intervals along the lines and filled with a flour and soya bean oil paste. Baiting is carried out for five successive nights regardless of the weather.

Nightly patterns of baits taken are frequently irregular as a result of unfavourable weather, although in general they increase from night to night. During the 18 months of sampling the average number of baits taken has steadily increased even though other sources indicate that a small drop in animal numbers has occurred. My conclusion is that animals have learnt to associate some sign, whether it be the sight or smell of stations, with the presence of a bait which they have come to accept over the months. Because bait stations are removed at the end of a sample and replaced at the beginning of the next, the baits taken increase from night to night as their positions are discovered by animals within their particular home-ranges.

A need to modify Bamford's (1970) sample design is evident from these results. Two options are available: (1) the first to stabilise the estimate by introducing a time based factor accounting for the learning process (Jane this symposium); (2) to side-step the problem by doing a series of one-hit counts. For example, an assessment of a control operation would require before and after samples consisting of five lines of 20 baits set in different localities on three consecutive fine nights. Total effort would equal about 12 man-days. The 95% confidence limits of the estimates would be about ± 25%, depending of course, on the distribution of the population. The technique can be used in a wide range of habitats - from native forests to open pasture, but, in general, is most applicable in areas which have good access.