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Author(s): Ross, James G.; Sam, Shona | Abstract: Possum numbers have been significantly reduced in many regions of New Zealand. However, research has indicated some unexpected consequences of possum control. At some sites, rat numbers have more than doubled 2 years after possum control. What this suggests is that the removal of a direct competitor has enabled a rapid increase in rat numbers relative to slower possum recovery. This has serious implications, as high rat numbers could inhibit ongoing possum ground control. To investigate this, an experimental trial was run where we tested the following research hypotheses by manipulating the rat density: i) Null hypothesis (H0) ‒ rat density has no influence on possum foraging behaviour around bait stations, ii) Alternative hypothesis (H1) ‒ rat density indirectly influences possum behaviour by removing all bait before possums can access it, and/or iii) Alternative hypothesis (H2) ‒ rat density directly influences possum behaviour by physically excluding them from bait stations. The experimental site was divided into 2 parts, a treatment block and a control (non-treatment) block. Rat control was undertaken using Victor® kill traps and 96 rats were removed over 6 nights (density estimated at 4.6 rats/ha). To quantify the effect of rat density on possum foraging behaviour, non-toxic bait stations were stapled to a tree every 10 m along 18 monitoring lines (n = 50). Possum behaviour was then monitored using both modified tracking cards and IR camera traps. Prior to trapping, 92% of all the baits were removed by rats on the first night. Following trapping, this reduced down to 8% in the treatment block. Rats turned up earlier than possums at the majority of the monitored sites (~1 hour before sunset). Before trapping, baits were only available 33% of the time when a possum visited a bait site (n = 15), and no baits were removed. After trapping, baits were available 100% of the time and 2 baits were removed by possums. These results support H1 and suggest that the smaller-bodied competitor can dominate food resources in NZ forests. This has the potential to make possum ground control more difficult when using control techniques that do not target rodents.

Author(s): Eason, Charles; Murphy, Elaine; Sam, Shona; Ross, James; Blackie, Helen; Henderson, Ray; Shapiro, Lee; MacMorran, Duncan; Gibson, Troy; Gregory, Neville; Conole, Daniel; Rennison, David; Brimble, Margaret | Abstract: Anticoagulant compounds are likely to play an important role in the control of commensal rodents for crop protection and conservation for the foreseeable future. However, there are concerns regarding their persistence and the development of more widespread resistance. We are seeking to retrieve and retain older alternatives as well as developing novel rodenticides. Our three-pronged approach is, firstly, to improve the performance of older non-anticoagulant rodenticides, such as sodium fluoroacetate (1080) and zinc phosphide; secondly to optimise the performance of 1st-generation anticoagulants; and thirdly, to identify alternatives to anticoagulant rodenticides with the same mode of action as para-aminopropiophenone (PAPP), which was registered in New Zealand as a predacide in April 2011. Zinc phosphide was also registered in New Zealand for the first time in 2011, and combinations of ultra-low-dose cholecalciferol with first generation anticoagulants are being advanced to provide the performance characteristics of a 2nd-generation anticoagulant with a lower risk of bioaccumulation and secondary poisoning.

Author(s): Eason, Charles; Murphy, Elaine; Ogilvie, Shaun; Blackie, Helen; Ross, James; Kavermann, Mathew; Sam, Shona; Statham, Mick; Statham, Helen; Lapidge, Steven; Humphrys, Simon; Henderson, Ray; MacMorran, Duncan; Gibson, Troy; Gregory, Neville; Harrison, Joanne; Giles, Gregory; Sammut, Ivan; Jansen, Paul; Conole, Daniel; Rennison, David; Brimble, Margaret | Abstract: In New Zealand, sodium fluoroacetate (1080) has been used for vertebrate pest control for several decades. Since the 1990s, some 1080 users have switched to brodifacoum for possum and rodent control because of its ready availability and ease of use. An awareness that field use of brodifacoum results in persistent residues provides the impetus to develop alternatives and provide new tools and greater flexibility. Looking to the future, we seek toxins which increasingly combine “low-residue” characteristics with humaneness, and more selective bait and delivery systems enabling better and more acceptable control of possums, wallabies, mustelids, rodents, feral cats, and rabbits. Experience gained in the 1990s with the introduction of cholecalciferol (Feracol®) and a cyanide pellet (Feratox®), which both kill possums without secondary poisoning, underpins the extension in 2009 of the Feratox® registration to include introduced Dama wallabies. To date, zinc phosphide has not been registered in NZ, despite its field use in Australia and the U.S. and low secondary poisoning risk compared with 1080. Research and registration dossiers are being assessed in 2009-10 for zinc phosphide containing products for possum and rodent control. Registration documents are also being prepared for a combination of cholecalciferol and coumatetralyl to provide a slow-acting alternative to brodifacoum for the field control of possums, rodents, and rabbits with low risk of bio-accumulation. Anticipated timelines for product availability are 2010 (zinc phosphide) and 2011-13 (cholecalciferol and coumatetralyl). Our intention now is to move beyond these conventional rodenticides and develop new vertebrate pesticides. For example, we are pursuing the registration of para-aminopropiophenone (PAPP) for humane control of stoats and feral cats, and a series of related novel toxins and other compounds that target the red blood cell for other pest species including rodents. PAPP products should be available in 2010, subject to registration approvals. New research initiatives in 2010 will increasingly result in a shift in focus to the development of novel rodenticides aided by new international research collaborations.

Author(s): Sam, Shona; Ogilvie, Shaun; Paterson, Adrian; McIlroy, John; Eason, Charles | Abstract: The use of infrared-flash camera traps has increased dramatically over the past ten years particularly for capturerecapture population studies of distinctly-marked species. However, to use capture-recapture with the more inconspicuous species, high-quality colour imaging (and therefore white flash) is required. A potential problem with white flash is that it may negatively affect behaviour, in this case at bait stations, therefore causing results that do not truly represent possum activity. Possums were used in this study to compare two different types of camera trap: infrared and white flash. Camera traps were placed to take images of possums visiting bait stations, and the number of possum visits was used to determine if white-flash cameras gave different results to infrared-flash cameras. The white-flash cameras had slightly higher possum visits than infrared-flash cameras but the difference was not significant (P=0.437). Over time, the number of possum events (P=0.62) and the amount of time possums spent at the stations did not differ significantly (P=0.81). There was also no difference in the amount of bait taken by possums at white flash compared to infrared stations (P=0.61). Results show possums are not likely to be affected by white-flash cameras compared to infrared-flash cameras. This study therefore showed that there is unlikely to be any behavioural disadvantage in using white flash over infrared, allowing white-flash cameras to be investigated for their potential in identifying individual possums, and as a monitoring tool in control operations.