Aerial Prefeeding Followed by Ground Based Toxic Baiting for More Efficient and Acceptable Poisoning of Invasive Small Mammalian Pests

Abstract

Introduced brushtail possums (Trichosurus vulpecula) and rat species (Rattus spp.) are major vertebrate pests in New Zealand, with impacts on conservation and agriculture being managed largely through poisoning operations. Aerial distribution of baits containing sodium fluoroacetate (1080) has been refined to maximise cost effectiveness and minimise environmental impact, but this method is strongly opposed by some as it is perceived as being indiscriminate. Although ground based control enables precise placement of baits, operations are often more than twice as costly as aerial control, mainly due to the high labour costs. We investigated a new approach to ground based control that combined aerial distribution of non-toxic ‘prefeed’ baits followed by sparse distribution of toxic baits at regular intervals along the GPS tracked prefeeding flight paths. This approach was tested in two field trials in which both 1080 baits and cholecalciferol baits were used in separate areas. Effectiveness of the approach, assessed primarily using ‘chewcards’, was compared with that of scheduled aerial 1080 operations that were conducted in outlying areas of both trials. Contractors carrying out ground based control were able to follow the GPS tracks of aerial prefeeding flight lines very accurately, and with 1080 baits achieved very high levels of kill of possums and rats similar to those achieved by aerial 1080 baiting. Cholecalciferol was less effective in the first trial, but by doubling the amount of cholecalciferol bait used in the second trial, few possums or rats survived. By measuring the time taken to complete ground baiting from GPS tracks, we predicted that the method (using 1080 baits) would be similarly cost effective to aerial 1080 operations for controlling possums and rats, and considerably less expensive than typical current costs of ground based control. The main limitations to the use of the method will be access to, and size of, the operational site, along with topography and vegetation density.

Attempting local elimination of possums (and rats) using dual aerial 1080 baiting

“…A peanut-butter-based bait would be one option (or use of baits even more attractive than peanut butter; Jackson et al 2016). As no bait type other than cereal is currently registered for aerial 1080 baiting, the second baiting might initially need to be conducted (as in this trial) with aerial pre-feeding, but hand-laying of the alternative 1080 bait type, which already has been demonstrated to be effective at operational scales (Morgan et al 2015). Another avenue of potential research could focus on determining whether pre-feed sequencing (e.g.…”

Wild Animal Tuberculosis: Stakeholder Value Systems and Management of Disease

“…This revealed strong public stakeholder support for the benefits of possum control, particularly the values placed on the observable effects of improved forest canopies and the positive impact on native bird, insect and plant species. The main criticism of possum control has subsequently been aimed at the methods used to cull possums, especially the use of sodium fluoroacetate (1080) by aerial application (49, 50).…”

Wild Pigs

“…In the United States and most other countries in the world, aerial application of rodenticide is typically used for invasive rodent eradication purposes rather than invasive rodent population suppression; however, in New Zealand, aerial broadcast of toxic baits (e.g., 1080) has been used for decades to suppress, rather than eradicate, invasive possums (Trichosurus vulpecula) and rats (Rattus spp. ; Morgan et al 2015). Currently, the U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) has two rodenticides registered with the EPA for island conservation purposes: one formulation of diphacinone pellets and two formulations of brodifacoum pellets (Witmer et al 2007b;Figure 10.7).…”