Reducing wildlife damage with cost-effective management programmes

Limiting the impact of wildlife damage in a cost effective manner requires an understanding of how control inputs change the occurrence of damage through their effect on animal density. Despite this, there are few studies linking wildlife management (control), with changes in animal abundance and prevailing levels of wildlife damage. We use the impact and management of wild pigs as a case study to demonstrate this linkage. Ground disturbance by wild pigs has become a conservation issue of global concern because of its potential effects on successional changes in vegetation structure and composition, habitat for other species, and functional soil properties. In this study, we used a 3-year pig control programme (ground hunting) undertaken in a temperate rainforest area of northern New Zealand to evaluate effects on pig abundance, and patterns and rates of ground disturbance and ground disturbance recovery and the cost effectiveness of differing control strategies. Control reduced pig densities by over a third of the estimated carrying capacity, but more than halved average prevailing ground disturbance. Rates of new ground disturbance accelerated with increasing pig density, while rates of ground disturbance recovery were not related to prevailing pig density. Stochastic simulation models based on the measured relationships between control, pig density and rate of ground disturbance and recovery indicated that control could reduce ground disturbance substantially. However, the rate at which prevailing ground disturbance was reduced diminished rapidly as more intense, and hence expensive, pig control regimes were simulated. The model produced in this study provides a framework that links conservation of indigenous ecological communities to control inputs through the reduction of wildlife damage and suggests that managers should consider carefully the marginal cost of higher investment in wildlife damage control, relative to its marginal conservation return

USING BIOECONOMIC MODELS TO MAXIMIZE BENEFITS FROM VERTEBRATE PEST CONTROL: LAMB PREDATION BY FERAL PIGS

The question “When should investment in pest control stop?” either explicitly or implicitly underpins decisions concerning pest control made at every level of enterprise or government, regardless of whether these decisions are tactical or strategic. Bioeconomic modeling provides a quantitative framework for considering the benefits and costs of alternative pest control strategies. In this case study, we develop 3 bioeconomic models that examine strategies based on helicopter shooting and 1080 poisoning, for reducing feral pig (Sus scrofa) predation of newborn lambs in wool-growing enterprises located in Australia’s rangelands. In the first model, marginal analysis indicated that helicopter shooting was more profitable than 1080 poisoning when pasture biomass was above 220 kg•ha-1, and was most profitable when feral pig density was reduced to 1.5•km-2. Below pasture biomass of 220 kg•ha-1, 1080 poisoning became more profitable than helicopter shooting. The second model added logistic population growth for pigs so that control could be simulated through time. While the net benefit from helicopter shooting was still maximized when applied annually, and the profitability of 1080 poisoning was still dependent on pasture biomass, the return on investment from both strategies increased markedly. While the third model, which added stochastic environmental variation, further increased the profitability of control, it also introduced uncertainty to the net benefits realized. For helicopter shooting, annual application remained most profitable

Modeling the cost-effectiveness of wallaby control in New Zealand

Bennett’s wallaby (Macropus rufogriseus) was introduced to South Canterbury in New Zealand’s South Island in 1974. The species rapidly increased in numbers, and by the 1940s had increased to levels where it had become a significant agricultural pest. In 1947, a coordinated wallaby control program employing teams of shooters commenced. However, wallaby numbers stayed high, and it was not until the early 1960s when aerially sown 1080 baits were used that a significant reduction in wallaby numbers was achieved. However, the need to de-stock areas prior to application of the baits prompted fanners to demand control by shooting teams rather than poison in order to achieve ongoing control. Wallaby control in South Canterbury is managed under a Regional Pest Management Strategy, relying on shooting as the primary form of control, but using aerially distributed 1080 baits and 1080 gel applied to broadleaf foliage to a limited extent when and where necessary. Wallabies are continuing to expand their range into the central alpine region adjacent to South Canterbury where they are becoming a conservation threat on public lands. In this study, we re-analyzed 13 years of detailed hunting return data in order to derive a synoptic model of wallaby population growth relative to density and prevailing rainfall. We also estimated cost-effectiveness models for control employing shooting teams, aerially distributed 1080 baits, and 1080 gel applied to foliage. We then explored the cost-effectiveness of alternative strategies for wallaby control by combining the models predicting wallaby population growth with those predicting variation in the cost-effectiveness of available techniques. The implications of this study for ongoing wallaby control for mitigation of agricultural and conservation impacts are discussed

Modeling the cost-effectiveness of wallaby control in New Zealand

Bennett’s wallaby (Macropus rufogriseus) was introduced to South Canterbury in New Zealand’s South Island in 1974. The species rapidly increased in numbers, and by the 1940s had increased to levels where it had become a significant agricultural pest. In 1947, a coordinated wallaby control program employing teams of shooters commenced. However, wallaby numbers stayed high, and it was not until the early 1960s when aerially sown 1080 baits were used that a significant reduction in wallaby numbers was achieved. However, the need to de-stock areas prior to application of the baits prompted fanners to demand control by shooting teams rather than poison in order to achieve ongoing control. Wallaby control in South Canterbury is managed under a Regional Pest Management Strategy, relying on shooting as the primary form of control, but using aerially distributed 1080 baits and 1080 gel applied to broadleaf foliage to a limited extent when and where necessary. Wallabies are continuing to expand their range into the central alpine region adjacent to South Canterbury where they are becoming a conservation threat on public lands. In this study, we re-analyzed 13 years of detailed hunting return data in order to derive a synoptic model of wallaby population growth relative to density and prevailing rainfall. We also estimated cost-effectiveness models for control employing shooting teams, aerially distributed 1080 baits, and 1080 gel applied to foliage. We then explored the cost-effectiveness of alternative strategies for wallaby control by combining the models predicting wallaby population growth with those predicting variation in the cost-effectiveness of available techniques. The implications of this study for ongoing wallaby control for mitigation of agricultural and conservation impacts are discussed