An investigation into the ecology and management of feral pigs (Sus scrofa) in the Macquarie Marshes, New South Wales

  • Jason Wishart

    Student thesis: Master's Thesis

    Abstract

    The Macquarie Marshes are one of the largest remaining inland semi-permanent wetlands in south-eastern Australia. They contain diverse flora and fauna, and provide important habitat for many colonial and migratory waterbirds. As a consequence, large areas of the Macquarie Marshes are listed as a Ramsar Wetland; a wetland of international importance. Feral pigs (Sus scrofa) are believed to be a key threatening process to the ecological integrity of this area. They are also believed to be a potential disease hazard and a significant impediment to surrounding agriculture. Despite considerable management efforts, feral pigs are abundant and widespread in the Macquarie Marshes. This project aims to provide a greater understanding of feral pig ecology and the effects of various management options on their abundance and damage to help refine future feral pig management in the region. Diet: This study was undertaken to identify which wildlife species are being consumed by feral pigs in the Macquarie Marshes, and to determine whether collection date, collection site or feral pig demographics influence predation levels. Stomach contents were analysed from 58 feral pigs that were shot during a routine aerial shooting campaign in the Macquarie Marshes during May 2011, September 2011 and March 2012. Feral pigs were largely herbivorous, with plant material occurring in 100% of stomachs and making up 94% of the food material that was consumed. In contrast, animal material occurred in 31% of stomachs and made up the remaining 6%. Of the animal material that was consumed, vertebrate prey occurred most frequently and in largest quantities. Reptiles and amphibians, particularly frogs, were the most common. No threatened reptile and amphibian species were recorded, and neither were any colonial or migratory bird species, or their eggs. It is possible however that some food items such as soft bodied invertebrates (gastropods, annelids or larvae) and/or eggs of ground nesting species may be underrepresented in the diet, because they may digest more rapidly in the stomach compared to other food items such as grasses, roots and vertebrates. Notwithstanding, collection date was the only factor that significantly influenced wildlife predation levels, with vertebrate wildlife prey occurring more frequently and in larger quantities during September 2011 and May 2012, which were also the warmest months. Further investigations are required to determine the relationship between feral pig density and the damage to reptiles and amphibians, so that appropriate management and monitoring actions can be developed. Stomach contents of feral pigs should also be analysed from additional months to more identify seasonal diet shifts. Unfortunately, this was not possible due to time and funding constraints. Activity patterns: This study was implemented to assess whether season and/or management option influenced feral pig activity patterns in the Macquarie Marshes, using remote camera technology. During the study, 34 remote cameras were positioned at permanent monitoring stations, on four different properties (four different experimental treatments) in four different seasons (summer, autumn, winter, spring). A total of 287 feral pig passes were recorded, 72.1% of which were nocturnal (night), 21.6% were crepuscular (dawn or dusk) and 6.3% diurnal (day). Feral pigs were most active between 05:00pm and 07:00am. Very few feral pigs were recorded on camera during daylight hours and none were recorded between 12:00 noon and 04:00pm. The study confirmed that feral pigs in the Macquarie Marshes were primarily nocturnal irrespective of season or the local management approach. Evidence of bimodal activity patterns was also apparent, with the first peak in activity occurring at approximately ~09:00pm and the second lower peak in activity occurring at ~06:00am. Results should however be interpreted with caution as feral pig activity patterns may have already been influenced by historical management, general farming practices and/or illegal hunting activity. Nevertheless, the study indicates that remote camera technology may be useful for monitoring daily feral pig activity patterns in relatively inaccessible areas, as the results obtained in this study were consistent with numerous other national and international studies. A potential shortfall with remote camera technology is that unlike radio telemetry, little information is provided on distances travelled by feral pigs. Bait attractants: This study was undertaken to assess the effectiveness of various bait attractants for their ability to enhance bait station visitation and bait-take by feral pigs in the Macquarie Marshes. During the trial, several different bait attractants including Carasweet®, meat meal, fish meal, vanilla and molasses (dry barley carrier), two common substrates (PIGOUT® and fermented barley) and a non-treatment (barley) bait were assessed. These bait attractants and bait types were trialled on four different properties, during two different seasons (summer and winter). The results demonstrate that none of the attractants tested (Carasweet®, meat meal, fish meal, vanilla or molasses) or commonly used bait substrates (PIGOUT® and fermented barley) were able to significantly outperform the non-treatment bait (dry barley). Despite this, Carasweet®, molasses, vanilla and fermented grain were consumed when they were discovered by feral pigs. All other attractants and the non-treatment received situations where feral pigs visited and did not eat. In addition, Carasweet® (4.3 ± 2.2 SE), molasses (3.33 ± 2.2 SE) fermented barley (2.10 ± 1.2 SE), meat meal (1.44 ± 0.09 SE) bait stations received a mean of ≥1 feral pig per station created, unlike the non-treatment which received a mean of 0.29 ± 0.20 SE feral pigs, per station. Non-significant results in the present study may have occurred because alternate foods were abundant during both trial periods and because the number of treatment replicates was relatively low. Hence, it is possible that the results are worst case scenario. Further investigations should be undertaken when conditions are drier and more suitable for baiting and trapping and a minimum of 32 replicates should be created for each attractant (Krebs 1999). Management The purpose of this study was to determine the relationship between index of feral pig abundance (number of feral pig passes per camera per night per site) and damage (ground rooting m2), and to assess the efficacy of various management options for managing feral pigs in the Macquarie Marshes. Four agricultural properties were used as study sites, each site was assigned a different feral pig management option and the study was undertaken over two years. The management options were aerial shooting and toxic baiting (treatment 1 site), aerial shooting only (treatment 2 site), toxic baiting only (treatment 3 site) and no management (non-treatment site). Index of feral pig abundance (IOA) and damage were monitored using remote camera stations and permanent 500 metre line intercept transects, respectively. The results indicate that feral pig IOA and damage were significantly positively related (r=0.46, n=15, p=0.04) in the Macquarie Marshes, with higher mean number of feral pig passes, per camera, per night, per site equating to a higher mean level of ground rooting per site. It was also evident that aerial shooting was useful for rapid initial population reductions when feral pig IOA was already high. None of the management options tested were able to significantly reduce feral pig damage within each study site. However, the damage results may have been affected by site flooding, as some line intercept transects were inundated during some monitoring events. The mean cost per kill for poison baiting was $420.44 ± $145.56 (SE), and the mean cost per kill for aerial shooting was $56.42 ± $23.13 (SE). Both aerial shooting and poison baiting were likely to be affected by feral pig IOA, and poison baiting was also likely to be influenced by season. The greatest removal rate of feral pigs from poison bait stations (75 ± 15% SE) occurred in January 2012 (summer). During future studies, each treatment should be simultaneously replicated on two or more properties that contain similar (high) levels of feral pig abundance. In addition, a minimum of sixteen permanent 500 metre line intercept transects should be created per site (Krebs 1999), and at least one round of poison baiting should be undertaken during hot and dry conditions. Unfortunately, this was not possible during the present study due to restricted site access, time and funding constraints, varying feral pig abundance throughout the region and above average rainfall. In summary, this project was able to provide valuable results in regards to the ecology and management of feral pigs in the Macquarie Marshes, New South Wales. The knowledge gained will assist in the development of future feral pig management strategies. It will also provide a platform for future research in this complex system.
    Date of Award2013
    Original languageEnglish
    SupervisorJim Hone (Supervisor), Steven Lapidge (Supervisor), Mike Braysher (Supervisor) & Stephen Sarre (Supervisor)

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