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Feral animal impacts


 
Feral pigs
 
Feral pigs have been present in Australia since early settlement. While they occur in all states and territories, they are most abundant in New South Wales and Queensland and are absent from large areas of the arid interior. Pigs are a very successful feral species; they are highly fertile, tolerant to a range of environmental conditions and have an opportunistic omnivorous diet. Males are typically longer, taller and heavier than females. While size can vary significantly, males usually range up to 115 kg and females up to 75 kg. Animals tend to live for less than five years. Sows make nests of vegetation, usually within 2 km of water. Females can breed by one year of age and litters usually comprise 5-6 Piglets, which are weaned after 2-3 months. If adequate food and water is available, pigs may breed throughout the year. 
 
Image source: Peter Fleming
 
Feral Pigs are opportunistic omnivores, meaning that their diet varies according to the seasonal availability of resources. Plant matter comprises the majority of their diet but they show a preference for succulent green vegetation, although they will eat fruit and seeds, foliage and stems, rhizomes, bulbs, tubers and fungi. They also eat a wide range of animal material including invertebrates, fish, frogs, reptiles, birds, eggs, mice, young rabbits, lambs and other small mammals and dead carrion. 

Feral pigs occur in a wide range of habitats and are considered habitat generalists. Key factors that influence their presence however are their limited tolerance to heat, and associated need for daily water and dense vegetation. They are restricted largely to our watercourses and floodplains in inland or seasonally dry parts of Australia. They prefer moist areas with reliable and sufficient food supplies, water, shelter and protection from high daily temperatures. Our regional wetlands and wet places are obvious locations where pigs can pose a major threat to their long term survival. 
 

Record observations of feral pigs to help protect to our wetlands - www.feralpigscan.org.au

 
 
Image source: John Tracey

Impacts on wetlands 

 
Given the preference of pigs to live in moist areas and dense vegetation, our regional wetlands are particularly vulnerable to damage by pigs They have been observed to impact many types of wetlands including marshes, swamps, creeks, floodplain wetlands and drainage lines. When wetlands begin to dry out, pigs can become concentrated around the water source, thus focussing the damage within an even smaller area. Those native wetland species and communities are likely to be particularly vulnerable damage by pigs. 

Feral pigs have been identified as a threat to about 40 threatened species listed under the Environment Protection and Biodiversity Conservation Act 1999. Ground dwelling, such as frogs and turtles, are particularly vulnerable to damage caused by digging pigs. There are examples of feral pigs preying upon both freshwater turtles. As examples: pigs were responsible for a loss of 96% of Northern Longneck Turtles at a freshwater ephemeral wetland in northern Australia; during the flooding that occurred in the Gwydir Wetlands in the season 2011/2012, feral pigs were responsible for eating young ibis chicks while adults were nesting in the flooded wetllands. In this case a helicopter shoot was successful in removing this threat to allow the Ibis to complete their nesting. Apart from direct impacts, competition for food resources between pigs and some native wetlands species has also been suggested as a potential issue i.e. Brolgas and Magpie Geese (wetlands tubers and bulbs). 
 
 
Image source: Peter West
 
Feral Pigs can also change the structure and composition of vegetation communities, reduce plant species diversity, reduce recruitment and survival through rooting and trampling and selective feeding, spread weeds and pathogens, and change nutrient cycles. The rooting behaviour of feral Pigs alters soil structure and processes, Feral pigs can foul dams and waterholes through their wallowing and defecation. Feral Pigs are carriers, either as hosts or vectors, of over 45 different parasites and diseases that may threaten stock, pets, native wildlife and humans. People may acquire diseases through consumption of pork, or via consumption of water or produce contaminated by feral pigs.

Feral pigs are therefore listed as a key threatening process and a Threat Abatement Plan has been prepared. 

Visit Feral Pig Threat Abatement Plan:
http://www.environment.gov.au/biodiversity/threatened/publications/tap/feral-pig-2017
 
 

Red Fox 

 
The red fox poses a serious conservation problem in Australia. Current estimates indicate that there are more than 6.2 million red fox and growing with a range extending throughout most of the continental mainland. The species became established in Australia through successive introductions by settlers in 1830s. Their spread across our region has coincided with the spread of rabbits, another invasive species also introduced in the 19th century that is a key prey of the red fox. Due to its rapid spread and ecological impact it has classified as one of our most damaging invasive and feral species. 
 
The red fox is a small to medium sized, burnished rusty red colour. Closely related to domestic dogs, the adult red fox weighs about 5 to 9 kg with males generally heavier than females. As is normal for feral species, they are very effective breeders with females coming into season for 2 to 3 days over 2 to 3 weeks in winter. Males are fertile throughout winter and early spring. Gestation lasts 51 to 53 days and a litter of 3-5 blue-grey cubs and weaning occurs at 4 to 6 weeks. The young appear from the den in late spring, at about 6 weeks of age. The cubs leave the den at about 10 to 12 weeks and by 6 months of age, are independent. Both sexes reach sexual maturity in their first year. Once foxes are independent they begin to move out of the family group to find, establish and mark new territories. The inherent ability of the red fox to rapidly establish new territories makes them a perfect feral species, for they adapt to compensate for any decline in food resources or changes in habitats.
 

Record observations of foxes to help protect to our wetlands - www.foxscan.org.au 

 
 
Image source: Bethan Lloyd via Feral Photos competitions 2016 (Invasive Animals CRC)
 
 
Image source: Mary Anne Addington, via Feral Photos Competition 2016 (Invasive Animals CRC)
 
By day, the red fox usually rests in a hide, this may be a hollow log, tree, an enlarged rabbit burrow or dense undergrowth. By night they hunt and patrol their territory. The red fox is best described as an opportunistic predator and scavenger. Largely carnivorous, foxes eat a diet of 300 g to 450 g/day of small prey in the weight range of 5 to 15 kg, including native animals, birds, rabbits, house mice and carrion. They readily eat fruits such as wild blackberry and insects such as scarab or 'Christmas' beetles. When food is abundant, foxes will often bury or 'cache' excess food. When food is limited in winter, cached food may be recovered.

Fox predation is recognised as having a serious impact on many native animals, and is considered to be a major contributor to extinction of some species. Species impacted include: brush tailed and yellow footed rock wallabies, bettongs, numbats, mallee fowl, pied oyster catcher, little tern, plains wanderer, bush stone curlew and the Murray River turtle. The species has been directly implicated in the extinction and decline of populations of Potoroo’s including the extinction of the Desert re-kangaroo. The spread of the red fox population also corresponds with declines in the distribution of several medium-sized ground-dwelling mammals, including brush-tailed bettongs, burrowing bettongs, rufous bettongs, bilbies, numbats, bridled tailed wallabies and quokkas.  Most of these species now only live in limited areas (such as islands) where red foxes are absent or rare. In 2016 researchers documented that some red foxes in Australia had learned to climb trees to look for baby koalas and other unsuspecting creatures such as gliders, dispelling the long-held belief that tree-dwelling creatures were safe from them. 
The wetlands and wet places of our region provides good habitat for foxes, places with heavy vegetation cover and abundant small prey. It is therefore important that fox control measures are regularly conducted in and at the margins of these wet areas so that the impacts from this feral pest can be reduced. Over time, it is hoped that regional fox control measures are successful in bringing their impacts on our native species down to negligible. 
 
Fox predation is therefore listed as a key threatening process and a Threat Abatement Plan has been prepared. 

Feral cats  

 
The origin of the feral cat in Australia is most likely dumped or neglected domesticated pet cats. 'Feral cats' are defined as those that live and reproduce in the wild (e.g. forests, woodlands, grasslands, wetlands etc) and survive solely by hunting or scavenging. They are predominantly solitary and nocturnal, spending most of the day in the safety of a shelter. Rabbits have aided their spread by providing food and burrows for shelter. There is typically one feral cat for every one to two kilometre square but this may be larger if food supplies are scarce. Feral cats are carnivores and can survive with limited access to water, as they use moisture from their prey. From the age of about one year, feral cats can breed in any season. They have up to two litters of about four kittens each year, but few of the young survive. Feral cats can fall prey to dingos, foxes and wedge-tailed eagles. Feral cats can carry infectious diseases, which can be transmitted to native animals, domestic livestock and humans. If rabies were to be accidentally introduced into Australia, there is a high risk that feral cats would act as carriers of the disease. They generally eat small mammals, but also catch birds, reptiles, amphibians, fish and insects - taking prey up to the size of a brush-tail possum. In pastoral regions, they feed largely on young rabbits, but in other areas like our wet areas of our region, feral cats prey mainly on native animals.
 

Record observations of foxes to help protect to our wetlands - www.feralcatscan.org.au 

 
Image source: Tim Doherty
 
We have lost 28 mammals already to feral cats and another 120 native animals are at direct risk from this invasive species. They have caused the extinction of some ground-dwelling birds and small to medium-sized mammals. They are a major cause of decline for many land-based endangered animals such as the bilby, bandicoot, bettong and numbat.  Feral cats can carry infectious diseases which can be transmitted to native animals, domestic livestock and humans. Research shows that the predators such as cats and foxes, have contributed to up to 60% of bird, mammal and reptile extinctions worldwide. Feral cats threaten the most species overall (430), including 63 that have become extinct. This equates to one-quarter of all bird, mammal and reptile extinctions – making the feral cat arguably the most damaging invasive species for animal biodiversity worldwide. Cats are believed to have also been a factor in the extinction of the only mainland bird species to be lost since European settlement, the paradise parrot. Many native animals that are found in our regions wetlands, are already struggling to survive due to other threats like habitat loss, so by reducing the number killed by this introduced and highly effective predator will allow their populations to survive.   

Predation by Feral Cat is therefore listed as a key threatening process and a Threat Abatement Plan has been prepared. 
 
 
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