New monitoring and control tools for simultaneously managing possums, rats and mice in New Zealand

Abstract

Simultaneously managing multiple pest species within one control operation is the most beneficial way to effectively manage New Zealand’s introduced mammalian pest species. Multi-species pest control can reduce multiple species and therefore is more cost-effective; less toxins are applied to the environment and there is reduced risk of meso-predator release. There are two main elements required for the success of a multi-species operation; an adequate multi-species control system and a multi-species monitoring system to provide accurate population estimates. This thesis describes two new tools (camera trapping and multispecies bait) for the simultaneous control and monitoring of possums, rats and mice.

Camera traps have been used internationally to monitor rare and cryptic species in the wild and their potential as a monitoring device and to provide answers to applied questions involving activity at bait stations was investigated in this thesis. Camera traps are especially useful for monitoring nocturnal behaviour although there was concern that white flash cameras may negatively affect behaviour providing results that do not truly represent species activity. Bait station activities of possums, rats and mice were compared at two camera trap types; infrared flash and white flash, to determine if white flash negatively influenced behaviour. Possums, rats and mice were not negatively affected by white flash cameras compared to infrared and may actually be attracted to the white flash cameras (P=0.437, P=0.285, P=0.928). The lack of significance indicated that white flash cameras could be used for behavioural and monitoring studies without affecting behaviour.

Little is known about the interactions between pest species at bait stations and how these interactions may influence the success of multi-species control. Camera traps were used to monitor interspecies interactions at bait stations that may influence the success of multi-species control operations. Rats were reduced in an area to investigate the influence they may have on mouse activity at bait stations. A control block was left with both rats and mice present. Camera traps were used to determine the activity of mice at bait stations before, two weeks and four months after an intensive rat trapping operation. Mouse activity increased significantly in the absence of rats, particularly at night, the time when rats were most active before they were removed (P=0.027). In the control block (with rats present) there was a significantly lower level of mouse activity at bait stations, indicating that rat presence lowers mouse activity at bait stations. Interspecies interactions between rats and mice may reduce the success of multi-species pest control operations where rats and mice are the target species.

White flash cameras were able to produce high resolution colour images at night which had potential to identify individuals for capture-recapture population estimates. Possums were used as an example species and a method was developed and tested to identify possum individuals. The identification method was tested by five different observers identifying possums from camera trap images. There was high observer variation however, on average 93% of the time observers could positively or tentatively identify an individual possum. Capture-recapture method was used to estimate a small possum population. Problems with camera placement and light variation limited the identification method, however, the identification method was able to identify a small population of possums and the method could be used for other species.

A newly-developed multi-species pellet bait matrix with the addition of cholecalciferol 0.4% was assessed in both cage and field trials for three target species: possums, rats and mice. The multi-species bait matrix was found to be significantly preferred compared with the current standard, RS5, for all target species in the field (possums P<0.001, rats P=0.04, mice P=0.005). The addition of cholecalciferol 0.4% yielded high reductions of possums, rats and mice in cage (100% reduction for all target species) and field trials (93.5, >83, and 85% respectively). Camera traps were found to be a useful tool for assessing bait effectiveness on free-ranging, wild animals. The cameras were also valuable for identifying the presence of low-density pest species that can be difficult to detect with conventional monitoring tools.

Camera traps were evaluated as a monitoring tool over a control operation by comparing the precision around the reduction estimate and cost effectiveness of camera traps against conventional monitoring devices. Camera traps were able to provide accurate multi-species monitoring in control operations (<15% precision around the estimate); comparable with conventional monitoring tools. Camera traps remain an expensive monitoring option for single species, however camera traps were cost-effective for multiple species monitoring over a five year monitoring period ($6,416 for camera trap monitoring, $8,420 for leg-hold trapping and tracking tunnels combined). Additional information that can be obtained from camera trap data such as spatial information and the camera trap ability to detect low-density pest populations make the camera trap a practical, cost-effective monitoring tool for multi-species monitoring.