Effect of prefeeding on foraging patterns of brushtail possums (Trichosurus vulpecula) about prefeed transects

Abstract

Context. Brushtail possums (Trichosurus vulpecula) are a major pest of native biodiversity and agricultural production in New Zealand. To maximise the effectiveness of control operations, prefeeding (free-feeding) of non-toxic bait before poison is often used, but the mechanisms by which it does so, remain unclear. One possibility is that prefeeding changes foraging patterns and space use in ways that increase the likelihood of possums finding and eating a lethal dose of poison bait.Aim. To determine whether prefeeding along transects increases possum activity on the transect, and if so, how long the effect lasts.Methods. We monitored the time that radio-collared possums spent within a few metres of 350 m of aerial wire laid along a transect.Key results. Initially, possums spent only 2.6 min per night in the vicinity of the wire, but after 20 kg of bait per kilometre were placed along the wire, that time increased 20-fold on the first night and remained high for the next four nights (by which time all of the bait had been consumed). After that there was a gradual decline in time spent near the wire over a further 18 days. The increased amount of time spent near the wire was the product of both an increase in the number of visits and the duration of those visits.Conclusions. We conclude that sowing prefeed in concentrated strips is likely to greatly increase the probability of possums rapidly encountering toxic bait sown along the same strips, especially where the toxin can be sown immediately after all of the prefeed has been eaten.Implications. Possum control operations can now be designed to apply much smaller quantities of toxic bait that will potentially reduce concerns about 1080 poisoning because of a move away from broadcast sowing operations that are intuitively disliked by many, to much more localised baiting regimes.

Bait aggregation to reduce cost and toxin use in aerial 1080 baiting of small mammal pests in New Zealand

“…The lesser reductions in rat and possum activity in the blocks that did not receive prefeed are consistent with previous research showing that the use of prefeed increases kill rates 14, 22. However, the results did not support the hypothesis that clustering of bait might obviate the need for using prefeed by ensuring most first‐time encounters by pests with toxic bait were with a lethal dose of 1080.…”

“…This is likely to be true for rats, as their smaller body size means that even small bait fragments are likely to be lethal (obviating the need for multiple bait encounters and the consequent need for overbaiting). For possums, however, it is likely that use of prefeed may also improve efficacy by causing animals to range more widely than usual, and that this helped them find toxic bait clusters more quickly 14…”

“…Possums actively seek out spatially aggregated bait deposits or ‘clusters’, especially when they have received prefeed (i.e. when they have been previously presented with a non‐toxic version of the bait in order to familiarise them with it) 14. Tests were conducted at an operational level to establish whether aggregating 1080 bait into isolated ‘strips’ or ‘clusters’, but leaving large unbaited gaps between such aggregations, could achieve an efficacy similar to that achieved with conventional ‘whole‐area‐coverage’ broadcast baiting.…”

Large‐scale pest control in New Zealand beech forests

“…The aim of the bird monitoring programme was to collect mortality and productivity data associated with 1080 operations for some species not previously monitored and to collect mortality and productivity data for species that had not been monitored during 1080 operations for more than 5 years: there have recently been substantial changes in 1080 sowing rates (Veltman & Pinder ; Veltman & Westbrooke ) and the use of prefeed (Warburton et al . ).…”

“…Mortality of some bird species during 1080 operations is known to occur (Veltman & Westbrooke 2011; Morris et al 2016), but more importantly, productivity increases after 1080 operations (Powlesland et al 1999(Powlesland et al , 2000(Powlesland et al , 2003. The aim of the bird monitoring programme was to collect mortality and productivity data associated with 1080 operations for some species not previously monitored and to collect mortality and productivity data for species that had not been monitored during 1080 operations for more than 5 years: there have recently been substantial changes in 1080 sowing rates (Veltman & Pinder 2001;Veltman & Westbrooke 2011) and the use of prefeed (Warburton et al 2009). Preliminary data analysis from six of the nine bird and bat species monitored during Battle for our Birds showed that some Kea (Nestor notabilis) were killed by 1080, and some Rock Wrens (Xenicus gilviventris) disappeared soon after the application of 1080 (although the cause of the latter is uncertain).…”