Aerial Shooting Research Articles

Method-Specific Costs of Feral Swine Removal in a Large Metapopulation: The Texas Experience

Author(s): Bodenchuk, Michael J. | Abstract: The methods used to remove feral swine include aerial shooting, trapping in large “corral” traps, drop nets, snaring, shooting in the daylight hours, and night shooting with specialized equipment. Each method has its utility as well as limitations. In areas with large connected populations, method selection may be based on the amount of land available for control, attitudes of neighbors towards control, time necessary to successfully implement control, and access to the habitat. Costs of control may be a secondary consideration. However, recognizing the relative cost of control in a metapopulation may assist managers when deciding between two or more equally appropriate methods. Texas Wildlife Services data were examined to determine the success rates and cost per animal removed by the various methods. Utility of each method and implementation strategies are also discussed.

Marine turtle nest depredation by feral pigs (Sus scrofa) on the Western Cape York Peninsula, Australia: implications for management

Context The west coast of the Cape York Peninsula (CYP) is a major nesting ground for three species of threatened marine turtle, namely, the flatback (Natator depressus), olive ridley (Lepidochelys olivacea) and hawksbill (Eretemochelys imbricata). Marine turtle nests in this area experience high rates of depredation and unpublished data from numerous studies have suggested that feral pigs are responsible for most nest losses. Aims The aim of the present study was to identify the relative magnitude of nest mortality associated with physical processes versus depredation and to distinguishing between two possible pig depredation scenarios. Methods We documented laying and mortality patterns on Pennefarther Beach (CYP) over a 49-day period in 2007. We partitioned mortality into components attributable to beach erosion, inundation and depredation and also assessed the relative magnitude of depredation associated with different nest predators. We used these data to test whether the temporal and spatial pattern of pig depredation was random with respect to patterns of nest availability. Key results The overall level of nest mortality was 40.2%. Depredation was responsible for 93% of nest losses. Pig predation was high, accounting for 89.6% of all mortality. Depredation occurred equally across nests of all three turtle species. Although nests were laid uniformly in both time and space, pig depredation was significantly clustered. Conclusions Depredation by feral pigs was the principal cause of turtle nest mortality in the present study. The pattern of nest destruction was consistent with the occurrence of pig depredation by single individuals in discrete feeding areas. Implications Current feral pig management involves aerial shooting. This is effective at removing large numbers of animals over large areas. However, aerial shooting is also expensive. Our results suggest that targeted monitoring and eradication of locally active individuals depredating nests may better manage pig impacts, specifically those on turtle nests.

Controlling disease outbreaks in wildlife using limited culling: modelling classical swine fever incursions in wild pigs in Australia.

Disease modelling is one approach for providing new insights into wildlife disease epidemiology. This paper describes a spatio-temporal, stochastic, susceptible- exposed-infected-recovered process model that simulates the potential spread of classical swine fever through a documented, large and free living wild pig population following a simulated incursion. The study area (300 000 km2) was in northern Australia. Published data on wild pig ecology from Australia, and international Classical Swine Fever data was used to parameterise the model. Sensitivity analyses revealed that herd density (best estimate 1-3 pigs km-2), daily herd movement distances (best estimate approximately 1 km), probability of infection transmission between herds (best estimate 0.75) and disease related herd mortality (best estimate 42%) were highly influential on epidemic size but that extraordinary movements of pigs and the yearly home range size of a pig herd were not. CSF generally established (98% of simulations) following a single point introduction. CSF spread at approximately 9 km2 per day with low incidence rates (< 2 herds per day) in an epidemic wave along contiguous habitat for several years, before dying out (when the epidemic arrived at the end of a contiguous sub-population or at a low density wild pig area). The low incidence rate indicates that surveillance for wildlife disease epidemics caused by short lived infections will be most efficient when surveillance is based on detection and investigation of clinical events, although this may not always be practical. Epidemics could be contained and eradicated with culling (aerial shooting) or vaccination when these were adequately implemented. It was apparent that the spatial structure, ecology and behaviour of wild populations must be accounted for during disease management in wildlife. An important finding was that it may only be necessary to cull or vaccinate relatively small proportions of a population to successfully contain and eradicate some wildlife disease epidemics.

The 2008 - 2009 Aerial Feral Pig and Feral Goat Shooting Program: A Case Study in Northern New South Wales, Australia

The 2008-2009 Aerial Feral Pig and Feral Goat Shooting Program aimed to reduce feral mammal infestations in the Barnard/Hunter River catchment areas, northern New South Wales (NSW), Australia, over a 2-year period, as well as to provide skills to landholders to manage vertebrate pests. By accomplishing these reductions in pest animal densities, it endeavoured to reduce impacts of feral mammals on soil and water resources and on native flora and fauna, thereby protecting ecosystems and giving benefits to the wider community. The NSW Department of Industries and Energy identified the control area, including the Barnard and Hunter River catchment areas, as having one of the highest populations of feral pigs in northern NSW. The area contains diverse and vulnerable ecosystems of woodlands, remnant rainforest, escarpment, and open grazing areas. Projects were designed to use best practice pest animal management methods, including aerial shooting, followed by a trapping campaign and ground shooting. Stakeholders included NSW National Parks and Wildlife Service, Armidale and Hunter Rural Lands Protection Boards, and up to 336 private landowners. Aerial shooting was undertaken in July, because winter is the most opportune season for this method. In 2008, a total of 913 feral pigs, 650 feral goats, 18 deer, and 4 wild dogs were destroyed. In 2009, 1,338 feral pigs, 900 feral goats, and 336 deer were destroyed, all of which were primary target animals. Trapping and poisoning were used to control feral pigs and an extensive ground-shooting program was put in place to control feral goats and the emerging deer problem. Monitoring of residual populations, through New England Livestock Health and Pest Authority property inspections, and assessment of damage caused by feral animals were undertaken at the conclusion of both projects. Ground trapping continues over a 4-month period, and ground shooting is ongoing and opportunistic.

The sociogenetic structure of a controlled feral pig population

In Australia, the feral pig (Sus scrofa) is a significant vertebrate pest that has an impact on agricultural production, public health and ecosystem integrity. Although feral pigs are controlled throughout much of their range, little is known about the impact that these control programs have had on the social biology, structure and the dispersal of pigs. To begin to address this, we collected demographic data and genetic samples from 123 feral pigs culled during a regional aerial shooting program over 33 pastoral properties in the semi-arid rangelands of southern Queensland, Australia. Sampling was carried out after two years of extensive control efforts (aerial 1080-baiting) and the samples therefore represented a controlled, persecuted population with a bias towards young animals. The analysis of 13 microsatellite loci suggested that females will accept multiple matings, females form loose mobs that appear to be highly dynamic social groups, and males will travel large distances between mobs. These data indicate that feral pigs in this population had a high level of social contact and form a single open population with no evidence of genetic (population) structuring. Such information may be important to integrate into management strategies, particularly the development of contingency plans regarding the spread of wildlife diseases.

Controlling feral goats by shooting from a helicopter with and without the assistance of ground-based spotters

The success of aerial shooting to control feral goats in arid and semi-arid environments has lead to its widespread use in rugged and more densely vegetated terrain elsewhere in Australia. In this experiment, the method’s effectiveness with and without the aid of ground spotters to assist in locating goats was evaluated in such terrain in the Chandler River Gorge near Armidale, New South Wales. The abundance of goats was estimated by applying a correction factor (1.45) to indices of abundance made by ground survey. Ground observers monitored success during the cull. Overall, only 31% of an estimated 462 goats were culled, at an average cost of $61 per goat. In all, 50% of the goats were in herds never seen by the helicopter crew, while the remaining 19% were individuals that escaped (17% unseen from the air) from herds that were shot at. Inconsistent culling success, combined with marked differences in the behaviour of goats in different experimental blocks, suggested that variable prior exposure to aerial shooting had a significant and confounding effect on the experimental outcome. Where goats had no prior experience of aerial shooting, culling success was 40% without spotter assistance and 59% with spotter assistance. Where there had been a history of aerial shooting the ground observers reported a marked increase in evasive behaviour, and the cull was only 21% even with spotter assistance. These results show that aerial shooting is not as successful in this type of terrain as has been assumed and suggest that its repeated or exclusive use will result in declining effectiveness as goats learn to evade the helicopter.

Feral goats in Australia: Impacts and cost of control

Feral goats are both a pest and a resource in Australia. They are thought to compete with domestic livestock for food and water and endanger the survival of native flora and fauna. However, there is little quantitative information on the impact of feral goats on agricultural production or conservation values. Their presence on agricultural land is partly tolerated since they can be commercially harvested by mustering or trapping at water points. Where commercial harvesting is not possible, other control techniques must be used. Aerial shooting is the most commonly used technique to remove goats in inaccessible areas, but it is expensive. This paper reviews the status and impacts of feral goats in Australia. It then outlines some cost of control models that predict the cost of controlling goats at different densities using aerial shooting in inaccessible terrain in the semi-arid rangelands of Australia.