Case study: Feral pig management in tropical rainforests of Queensland

The rainforests of Queensland’s Wet Tropics World Heritage Area (WTWHA) cover approximately 900,000 ha and are important habitats for numerous endemic, threatened and endangered plant and animal species. The unique rainforests are a focus for biodiversity conservation and nature-based tourism.

Feral pigs (Sus scrofa) are regarded as a major vertebrate pest in the WTWHA due to their negative environmental and economic impacts. The rooting behaviour displayed by foraging pigs causes soil disturbance, which impacts on soil structure, soil invertebrate (eg earthworms) populations, nutrient and water cycles, and plant species regeneration. The economic impacts of pigs include damage to agricultural production, the costs of control and the transmission of diseases such as leptospirosis. To reduce these negative impacts, various management methods have been applied by the government and private landholders, including trapping, hunting (using dogs and/or rifles), fencing and poison baiting. Although potentially the most effective and efficient method5, use of poison baiting in the rainforests has been discouraged because it can potentially kill native fauna species that have similar foraging habits and preferences to pigs. Consequently, the WTWHA management authority encourages trapping.

This study was based around the Daintree bioregion, located in the northern section of the WTWHA. The Daintree rainforests are of the greatest conservation value in the WTWHA because they have the highest numbers of endangered regional or ‘of concern’ ecosystems. It is a conservation priority to understand the magnitude of the ecological impacts of pigs and explore the potential use of target-specific poison baiting. Understanding the social-human dimensions of pig management is also key to successful management. This is because various stakeholder groups exist in the WTWHA, including farmers, pig hunters, tourism operators, tourists and Aboriginal communities, and each group may have different perceptions of pigs and interests in pig management.

Aims

This project aimed to:

  • increase the understanding of the ecological impacts of feral pigs in rainforest ecosystems
  • assess different methods for baiting pigs that minimise the impacts on native species in the WTWHA
  • investigate novel frameworks for cooperative management of pigs in the WTWHA, and
  • determine the perceived socio-economic and ecological costs and benefits of pigs and their management implications in the WTWHA.

Partners and management

The project was undertaken in partnership with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), the University of Queensland (UQ), James Cook University (JCU), the Wet Tropics Management Authority (WTMA), Queensland Government, Australian Wildlife Conservancy, Animal Control Technologies Australia (ACTA) Pty Ltd and the former Douglas Shire Council (now Cairns Regional Council). The project was funded by the Invasive Animals Cooperative Research Centre (IA CRC).

Process

The ecological impacts of feral pigs on rainforest dynamics were measured in terms of a range of earthworm, soil, litter and plant characteristics. The impacts were assessed by comparing two types of plots: fenced areas where pigs were excluded for two and 14 years, and unfenced areas at continual risk of pig damage in both the wet and dry seasons.

To determine the target specificity of poison bait, non-toxic manufactured PIGOUT® bait was exposed to both pigs and non-target species. Target specificity of the bait was tested based on the fact that feral pigs are omnivorous, fossorial/digging and nocturnal. Three types of bait presentation or composition were looked at: 1. Omnivore (fish flavoured) vs vegetarian (non-fish flavoured) composition of the bait 2. Surface-laid omnivore bait vs buried omnivore bait (at 10 cm), and 3. Restriction of bait availability to nocturnal hours (30 min after sunset until 30 min before sunrise). Seasonal variation in bait take was examined by presenting omnivore bait on the ground surface during each of nine bi-monthly sampling periods.

Stakeholders’ attitudes toward feral pigs and pig management methods were explored through interviews and/or surveys. Aboriginal rangers were interviewed on behalf of members of their communities.

Features of the study

This case study comprised four important features, investigating both ecological and human dimensions of the management of feral pigs:

  • Ecological impact assessment: Evaluating the short-term and long-term effects of pigs on the rainforest using pig exclosures.
  • Product risk assessment delivery: Testing target-specificity of feral pig baits in omnivore-rich communities where non-target species share similar dietary preferences to pigs.
  • Anthropology of feral pig management: Exploring the conflicts in feral pig management particularly with regards to use of hunting as a control technique.
  • Socio-economic implications of pigs and pig management methods: Assessing the perceived socio-economic and ecological values of feral pigs for different stakeholder groups and their views on pig management methods.

Results

Ecological Impact Assessment

  • Feral pigs did not have a strong impact on any of the measured aspects of rainforest dynamics (eg earthworm biomass, soil moisture, soil compaction, litter biomass, litter moisture, plant seedlings, plant saplings and trees).
  • Seasons had a greater impact on rainforest dynamics than feral pigs in both the fenced and unfenced plots.
  • The findings above contradict the obvious visual difference between the fenced and unfenced plots. The results could have been influenced by edge effects produced by small plot size.

Product risk assessment delivery

  • Manufactured baits PIGOUT® were rarely taken by feral pigs in the Daintree but were highly acceptable to dingoes. This was likely because the diet of pigs in the rainforests was more fruit-driven, but dingoes mainly took the baits in their breeding season.
  • There were no seasonal patterns in bait consumption by non-target species.
  • Nocturnal bait distribution effectively prevented diurnal omnivores (eg the yellow-spotted monitor) from encountering and consuming bait. But given their low bait consumption, nocturnal baiting would not be worthwhile.
  • In contrast to nocturnal bait distribution, burial was easy to implement and substantially reduced the number of non-target native omnivores that consumed bait, but burial did not reduce bait-take by dingoes.
  • Follow-up studies examined whether non-target small mammals could be deterred by factors that increased their predation risks. The results were:
    • Illumination at bait sites using LED lights reduced bait consumption by small mammals without inhibiting bait-take by pigs.
    • Broadcasting pre-recorded calls (vocalisations) of feral pigs or dingoes at bait sites did not deter non-target small mammals from feeding on bait.
  • Follow-up studies also found that:
    • Unprocessed starch-rich bait reduced dingoes’ bait consumption.
    • Bait-take by small non-target omnivores was reduced by use of a physical barrier to baits (eg a plastic box covering baits) with small portions of an alternative decoy food source around the bait sites.

Anthropology of feral pig management

  • Control techniques such as trapping and hunting, are significant to some communities because of social relationships formed by trappers and hunters. Recognition of this can benefit pig management and lead to more socially supportive control of pigs in the local area.
  • Pest control technologies may be subject to resistance not because of opposition to features of a technology but because of how its implementation ‘threatens’ activities important to certain hunters and their identities.

Socio-economic implications of pigs and pig management methods

  • Almost unanimously, the environmental costs of pigs were perceived to be significant, as their impacts did not match stakeholders’ perception of ‘good forest health’.
  • Significant agricultural damage was limited to a minority of farmers, and feral pigs had negligible economic implications for rainforest tourism in the WTWHA.
  • Social benefits were attributed to feral pig control as it is a recreational activity for pig hunters and a customary activity for Aboriginal people in remote areas. The meat obtained from hunting was also valued as a food source for those Aboriginal people.
  • Overall pig management was regarded as the responsibility of the government.
  • The restrictions posed on the ability of locals to manage pigs in national parks and stakeholders’ higher expectations of management outcomes (eg eradication), both resulted in their dissatisfaction with the current pig management.
  • Trapping was the most accepted method while there was general antipathy toward 1080 poison baiting because of stakeholders’ concerns about target specificity. Social acceptability of poisoning, however, may become higher once humaneness issues are overcome (eg baits using sodium nitrite) and baits are excluded from non-target animals through the use of self-resetting hoppers (HogHopper™).

What worked and why

  • In assisting fieldwork, numerous networks were developed with government agencies, researchers and industry groups.
  • Throughout the baiting trials, camera trap sampling was a useful tool for monitoring changes in pig population abundance over time, particularly in response to management actions.
  • Contextualising issues of feral pig management within its broader social and historical contexts highlighted how disagreements over feral pig management, including resistance to pig control technologies, could be socially and historically determined.
  • A one-page, concise tourist survey format encouraged higher response rates. Aboriginal rangers, who worked in the public domain, were easily approachable.

What didn’t work and why

  • The start of fieldwork was delayed due to the process of obtaining an Aboriginal Research Council approval from Traditional Owners which highlights the need to seek this and other approvals as early as possible.
  • Seasonal variation in bait acceptability by pigs could not be tested because there were few independent instances of bait encounter or consumption by pigs in the field.
  • Communication difficulties arose with ecologists due to the differences in the nature of quantitative ecological data and qualitative social research data.
  • Tourists travelling the Daintree by bus were hard to survey owing to their tight schedules.
  • Perceptions of members of Aboriginal communities were not explored because of the anticipated lengthy human ethics application.

Conclusion

The ecological impacts of feral pigs may need to be investigated further. Poison baiting has the potential to be an effective management tool if non-target issues are resolved with an aid of HogHopper™. Nonetheless, other management tools such as trapping and hunting could be simultaneously utilised for socially beneficial and acceptable control of pigs.

Author Invasive Animals CRC
Year 2014
Publisher Invasive Animals CRC
Pages 4
ISBN/ISSN PestSmart code: FPCS2
Control method Integrated Pest Management
Region QLD
Documents PestSmart Case study: Feral pig management in tropical rainforests in Qld   [660kb PDF]
Links PestSmart Toolkit for Feral Pigs: www.pestsmart.org.au/pest-animal-species/feral-pig/