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HWC FACT SHEET – CONTROL OF RABBITS AT THE HUNTER WETLANDS CENTRE Introduction Hunter Wetlands Centre Australia (HWC) is an internationally recognised Ramsar wetland. In order to protect our fauna and flora we have a pest control program, which recently saw rabbits start to enter the property again after many years of absence. With assistance from the Hunter-Central Rivers Catchment Management Authority (CMA), HWC was able to look at setting up a monitoring and control program to prevent the establishment of the rabbit pest on the site. This fact sheet provides an insight into this program and pest problem. History The European rabbit (Oryctolagus cuniculus) is native to north-western Africa, Spain and Portugal. The first successful introduction of rabbits to the Australian mainland is thought to have originated from a shipment of wild rabbits in 1859 to ‘Barwon Park’, near Geelong. The spread north and west was rapid, by 1886 they had reached the Queensland border. European rabbit Oryctolagus cuniculus Impacts The rabbit is considered to be Australia’s most damaging vertebrate pest and has adverse effects on pastoral and crop industries, as well as native fauna and flora. Native fauna suffer from direct competition with rabbits for food and shelter. Grazing, browsing and ringbarking of native flora have caused declines in native species and facilitated the invasion of exotic species. Rabbits are commonly believed to cause damage only when they occur in higher numbers, but in areas of low productivity, densities as low as one rabbit per hectare can prevent native plant regeneration. Erosion caused by rabbits in a gully in South Australia Distribution Rabbits now inhabit approximately 4 million sq. km of Australia, mostly south of the tropic of Capricorn. They have become established in environments ranging from sub-alpine areas to stony deserts, and from sub-tropical grasslands to wet coastal plains; but particularly in areas with Mediterranean climates. Habitat Rabbits prefer short grass areas (naturally semi-arid areas or heavily grazed pastures), with harbour (e.g. warrens, blackberries, fallen logs, native vegetation) nearby. In suitable habitats, most rabbits live above ground and need burrows only for breeding. Diet Rabbits are herbivorous and eat a wide variety of plants, including crops, roots, pastures, young trees and young vines. as calculated from maintenance requirements, approximately nine rabbits are equivalent to one DSE (dry sheep equivalent). Rabbits can graze plants to ground level and prefer soft, short and succulent plants rather than woody or stalky taller species. Grazing generally continues throughout the night for 2.5 to 6 hours. Reproduction Rabbits can breed at any time, provided there is feed. Both males and females reach sexual maturity between 3 and 4 months of age. The gestation period for rabbits is 28 to 30 days. Under very favourable conditions an adult female can produce seven or eight litters in a year, but more commonly three to five. Mortality Two of the most devastating diseases to rabbits are myxomatosis and rabbit haemorrhagic disease (RHD), commonly known as rabbit calicivirus disease (RCD). This can commonly cause 70% mortality. These diseases require vectors, close contact, mosquitoes or rabbit fleas to be present and active. This should not be relied on as primary control methods. Besides the fox, dingo, cat and dog, there are a number of avian species that prey on the rabbit in Australia. Movements and home range Rabbits are most active from late afternoon until early morning. Daily movements are generally within 150 to 200 m of the warren, but this distance can increase during drought (up to 1500 m has been observed), or decrease during the breeding season. 1 Rabbits at a waterhole within the myxomatosis trial site on Wardang Island, South Australia in 1938 MONITORING RABBITS AT THE HUNTER WETLANDS A very elusive rabbit at the HWC photographed out grazing late in the afternoon. Different methods can be used to monitor rabbit abundance on site, HWC uses: Spotlighting Night-time counting, using spotlights, either on foot or from vehicles, has been used for many years to survey animal species such as the rabbit, Oryctolagus cuniculus. This is mainly because spotlighting is easy to do and can cover large areas in a relatively short time. Warren counts and harbours Estimation of rabbit abundance from warren counts has been used in Australia since the1970s, when changes in the use of burrows were found useful for estimating changes in the number of rabbits using the burrows. Warren counts can be as simple as counting the number of active or inactive burrow entrances and using it as an index of rabbit abundance. Dung counts The dung (faecal pellets) of many species is more conspicuous than the animals themselves, especially during the day in the case of predominantly nocturnal species such as the rabbit. Counting the dung of rabbits offers a relatively easy way of monitoring rabbits during daylight hours. Dung counting can be as simple as walking a transect and recording the number of pellets via a 1 to 10 scale of density. Other Rabbit Signs Other signs of rabbits can be used to monitor rabbit activity and abundance. These signs include tracks, bait station visitation and diggings. Counting tracks can be passive (animal behaviour is not altered by detection; e.g. by placing sand plots across a road or track) or active (animals are attracted by a lure, e.g. by using scent and bait stations). Track counts are used predominantly for elusive animals or those found in low densities, such as foxes and wild dogs. Track counts using sand plots that are swept clean each day have been used successfully for rabbits where other more commonly used monitoring techniques were not feasible and may be useful in areas where vegetation or terrain make other counting methods difficult. Bait stations can be used to monitor rabbit abundance by using free-feeding or toxic bait. Using free-feed stations can indicate where ‘hotspots’ of rabbit activity are, whereas monitoring toxic bait station activity will measure the efficacy of Monitoring Technique Advantages Disadvantages Walked Spotlight Counts Counts can be highly unreliable Sightability can be effected by vegetation unreliable method in wet and windy conditions Warren Counts reliable measure indicates long-term rabbit-proneness and May require specialist help warrens may be difficult to detect in sand-dune areas can estimate total rabbit abundance per land type warren ripping costs can be estimated drought impractical in areas where rabbits use few or no warrens can be done in areas where rabbits do not use cannot be used for some time after rain rate of dung production varies with season and quality of Dung Counts Sand Plots Quick & simple Can be done by one person Suitable for small areas Helps locate rabbit feeding grounds for poisoning infestation during warrens limited effect of wind, temperature, vegetation or terrain flexible timing of sampling and can be done during the day flexible timing of sampling and can be done diet not an accurate measure of absolute numbers but good for assessing relative numbers sign may be destroyed by weather or human and vary during the day seasonally not an accurate measure long set-up time not always appropriate for use with rabbits Non-toxic Bait Stations flexible timing of sampling and can be done Diggings quick and simple flexible timing of sampling and can be done sign may be destroyed by weather or human and vary during the day seasonally not an accurate measure long set-up time sign may be destroyed by weather or human and vary seasonally not an accurate measure during the day 2 control programs. Bait stations are portable and can be moved from one site to another as needed. However, a drawback to using bait stations is that relatively large proportions of rabbit populations are reluctant to enter bait stations. Counting the number of rabbit diggings or scratchings along a standardised walk transect will also give an idea of abundance. Monitoring methods, eg.: Sand plots; Non-toxic bait stations; Diggings; Live trapping; Warren trapping of live rabbits, see table page 2. RABBIT CONTROL Integrated rabbit management Optimum control of rabbits is best achieved by integrating more than one control method. Reliance on a single control method will most likely lead to ongoing problems. HWC needs to understand the rabbit problem on their grounds, and then develop an integrated control strategy to give an economic and sustainable control of this pest. The best returns from rabbit control mainly come from a regional approach involving neighbours working together. Warren and harbour destruction The best way to control rabbits long-term, is to destroy their warrens and hiding places. This means that they cannot survive the hot summers, and cannot rear their young successfully. Rabbit populations usually take many years to recover from a thorough warren destruction program. Recovery will even take longer if the ripped warrens are regularly checked and follow-up work done when needed. Successful warren destruction programs rely on working out the extent of the rabbit problem by surveying the area for signs of rabbits, e.g. active rabbit warrens, with holes that are obviously being used, especially the doe’s strenuous hole cleaning just before she gives birth. This leaves a streak of dirt which is often visible for some distance. Other signs are fresh rabbit droppings, and chisel-shaped teeth marks on food plants. Before taking to the area with a tractor and ripper, proper planning can save time and effort. Marking all of the warrens will save valuable time. Obviously this part of the job is very labour intensive. GPS technology is an invaluable aid to planning the most efficient way to cover all warrens in an area. Usually the best time of year to destroy rabbit warrens is in the late summer, when rabbit numbers are already low and the soil is dry and will collapse more easily. Effective ripping of warrens relies on deep ripping with close ripping lines and the ripping extending past the warren. Ideally, the ripper tines should be to a depth of 900mm, at a spacing of 500mm. After ripping one way it should be repeated at 90°, this process is known as cross-ripping. Particular equipment may be useful for particular jobs. To protect native vegetation, a single ripper tine on a front end loader or a backhoe can do the trick. Blade ploughs may be adequate for light or loamy soils, and disc cultivators may be successful in cultivated areas where rabbit numbers are low. Poisoning 1080 The most commonly used poison to control rabbits is sodium monofluoracetate, commonly known as 1080. 1080 must only be used under the supervision of a qualified operator. Interestingly, many native plants, have naturally high levels of 1080, and some native animal and bird species have a resistance to 1080. Pindone© Is a anticoagulant compound which acts in a similar way to common rat poisons. Pindone© can be used where 1080 cannot be used. Pindone© also has an effective antidote, which is not the case for 1080. These poisons are not to be used lightly. If they are used incorrectly, native mammals and birds, livestock, pets and even humans can be at risk. In addition, careless use can lead to the poison being ineffective, particularly through rabbits developing resistance to the poison, or even becoming shy about eating the bait - bait-shyness. Both the effectiveness and selectivity of poisoning rabbits are enhanced by pre-baiting with non-poisoned bait and ensuring that only rabbits are taking the bait; using bait that is most attractive to rabbits; use minimum concentration of poison sufficient to kill rabbits; placing the bait in the prime feeding areas of the rabbits; and collecting the carcasses of poisoned rabbits to prevent secondary poisoning of non-target species. Fumigation Fumigation is used if warrens have been re-opened after ripping, or in areas which cannot be ripped. Static fumigation uses tablets which produce phosphine gas when damp. Predators, parasites and diseases One major rabbit predator, the European fox, and cats have also become feral in Australia, however, they cause problems of its own amongst native animals and livestock. Many native raptors, such as eagles, now have rabbits as a 3 large part of their diet. Generally, predation may help slow the rate of increase of the numbers of rabbits, but is not enough in itself to make much difference. Biological controls are very useful, even spectacular at times, but they are not enough by themselves. There is a need to integrate conventional control methods with biological control, especially when rabbit numbers are low, to maximise the benefit of the biological control agents. HUNTER WETLANDS CENTRE SITE PLAN 0 50 100 150m Predator proof fences Fences can be used to prevent re-infestation of high-value areas, eg. farm, bush regeneration area or a wildlife sanctuary. The Hunter Wetlands Centre is predator fenced on all sides except the natural Iron Bark Creek boundary that connects us to broader environments such as Hexham Swamp... Whether rabbits are controlled by disease, poisoning, warren destruction, exclusion or a combination of these methods, the point is not how many rabbits are killed, but how many are left behind. An 80% level of control sounds great, but given an average year, the remaining 20% of rabbits only need one year to build up to their previous levels. A level of at least 90 to 95% control is needed to have any long-term effect. And, of course, an even more important point to remember is that though killing rabbits may sound inhumane, wild rabbits are affecting the survival of native Australian plants and animals. It is our responsibility to control them. We brought the European rabbit here in the first place - they are an invasive pest. Competition and grazing by the feral European Rabbit Ocryctolagus cuniculus was listed as a Key Threatening Process on Schedule 3 of the Threatened Species Act 1995. Grazing and burrowing by rabbits can cause massive erosion problems, reduce recruitment and survival of native plants, and alter landscapes. Rabbits threaten the survival of a number of native animal species by altering habitat, reducing native food sources, displacing small animals from burrows and attracting introduced predators such as foxes. At the Hunter Wetlands Centre it has been observed that the reduction in the number of foxes has led to an increase in the number of rabbits, which in turn has altered the habitat for several species of birds and animals. For example through grazing competition rabbits compete for food with the native Bandicoot. There has been extensive revegetation of the site over many years, and recently it has been noticed that new plantings of nursery propagated plants are ideal food for rabbits, who do major damage to new plantings which have to be replaced, which is a costly exercise for the HWC. Volunteers interested in participating in this project please contact the site manager Paul Trute in person at the Hunter Wetlands Centre office or email: [email protected] References: NSW Dept. of Primary Industries, Monitoring Techniques for Vertebrate Pests Rabbits Bruce Mitchell & Suzanne Balogh. Hunter Wetland Centre Off the roundabout, Sandgate Road, Shortland NSW 2307 Photos: Wikipedia & HWC PO Box 292, Wallsend NSW 2287 Ph: 4951 6466 Fax: 4950 1875 Email: [email protected] This project was made possible with the assistance of the Hunter-Central Rivers Catchment Management Authority using funding from the Australian Government's Caring for our Country Web: www.wetlands.org.au Open 9am to 4pm - 7 Days Spoonbill Cafe: [email protected] 4