Briefing note on Kangaroo Management - II Yorke Peninsula Natural Resource Management Group Photo: Ivan Clarke Jodie Reseigh and Geoffrey C. Bishop June 2010 Methods to assess impact of kangaroos on biodiversity and production
In order to determine the methods that are required to assess the impact of kangaroos on biodiversity and production, it is important to have an appreciation of the diet of kangaroos. Kangaroos are predominantly specialist grass eaters, but some species consume smaller amounts of other vegetation. The Red Kangaroo's diet also includes herbs and shrubs. When pasture biomass declines, Western Grey Kangaroos alter their diet to also include herbs and shrubs. The Euro diet is similar to kangaroos, with their diet consisting predominately grasses with a small component of forbs. There are various methods that enable estimations to be made of the impact of kangaroos in both biodiversity and production areas. There are a couple of steps in determining the impact of kangaroos: the first is to determine if kangaroos are grazing particular areas and the second is to determine the impact of grazing on crops, pasture or native vegetation. The presence and number of kangaroos may be determined through:
Observation of kangaroos in monitored areas; Locations of kangaroo faeces; Locations of kangaroo tracks; and surveys.
In situations where kangaroos are the dominant grazer (i.e. livestock are excluded such as in National Parks or cropped paddocks) a combination of methods including observation of animals and the locations of faeces and tracks are used to determine the grazing activity of kangaroos. Research has found that there is a direct relationship between faecal pellets and feeding activity of kangaroos and can be used as a method for estimating kangaroo densities (number of kangaroos per unit area). Tracks alone may only indicate movement of kangaroos through the landscape and may not have a direct relationship to the number of animals present in an area. Having ascertained that kangaroos are present and made an estimate of numbers, the impact of the kangaroos needs to be determined. This can be undertaken in a number of ways depending on the type of area being monitored and the parameter being monitored, i.e. crop, pasture, shrub seedlings.
Production areas (including crops and pastures) parameters
o Records of grazing damage; o Plant cover (often measured as percentage cover); o Area
o Area of tracks; and o Area of hip holes (areas where kangaroos bed down
Biodiversity areas parameters measured include:
o Recruitment of indicator species; o Survival of species; o Pasture
o Species composition of areas; o Other plant parameters such as plant height; o Grazing damage to plants.
For example, in an experiment where seedlings of Kangaroo Grass were monitored, parameters measured included seedling survival rate, signs of grazing and the species of herbivore responsible (if this could be determined from bite marks). Through the use of statistical techniques parameters such as these can be related to the grazing impact of kangaroos and other herbivores. Where there are other grazing animals present, grazing exclusion techniques may need to be used. Grazing exclusion is enabled through the use of small (or large) grazing exclosures, to differentially exclude grazers including kangaroos, livestock - sheep/cattle, rabbits and any other grazing animals that may be present. For example, in a situation where there is rabbit, sheep and kangaroo grazers, fencing combinations would include:
Areas to exclude sheep (but allow kangaroo and rabbit grazing);
Areas to exclude kangaroos (also exclude sheep); fenced with tall
Areas to exclude all grazers, sheep, kangaroos and rabbits; fenced
with tall welded wire mesh with rabbit-proof wire around the lower portion of the fence;
Control areas, all grazers, kangaroos, rabbits and sheep having
These techniques of fencing allow researchers to determine the individual impact of each grazer. These are then related to the impact of the grazing animal, as described below.
Control techniques of kangaroos
A range of techniques are available to control kangaroos. They include options available to landholders and some options which are only available with specialist help, and they include:
Controlling access to watering points Fertility control Ultrasonic devices to deter kangaroos Use of specialist fencing to exclude kangaroos Use of predator urine to deter kangaroos Predators Destruction of animals.
Controlling access to watering points The provision of watering points on farming and grazing properties has allowed kangaroos to spread over a greater area and has changed where kangaroos are distributed. Due to the reliance of kangaroos on water for their survival, controlling access to water is thought to be one method of controlling kangaroo numbers in a locality. The controlled access to watering points is aimed at encouraging kangaroos to find alternative sources of water and therefore reducing the grazing impact around the water source. Two primary methods of control at watering points are:
Turning the water off (or in the situation of dams - filling them in); or Restricting access to watering point through fencing.
Additionally, the use of watering points particularly during drought by kangaroos presents an opportunity to facilitate their destruction, as kangaroos will congregate around the water source. Turning off the water supply is easiest undertaken where there is trough water, however in many situations water is provided through dams or bores. This presents a more complicated situation and is most suited to land designated to conservation rather than land used primarily for agriculture. However, there are concerns about the closure of watering points and the likely impacts on other wildlife and also about where kangaroos would likely relocate (often other agricultural land). In effect, this may simply move the kangaroo problem from one farm to another. Kangaroo access to water can be restricted through strategically placed electric fences; one such method is termed the 'Finlayson electrified trough'. In this instance, a low lying electrical conductor is set around a watering point to selectively exclude kangaroos from water. The electrified trough may also deter sheep from grazing but this may be overcome through the use of a timer - i.e. only electrifying the wires at night when kangaroos are grazing. Results from the use of the Finlayson electrified trough, or its equivalent, have had mixed results. Electrified troughs were effective in moving kangaroos to non-electrified water sources, but in large areas (~100,000 ha) troughs were only effective for approximately two weeks, and after that time kangaroos learnt to drink at the trough without receiving an electric shock. Kangaroos learnt that if their tails were lifted clear of the electric wire while drinking or alternatively approached the trough from the side and changed the positioning of their body to be parallel to the trough and the electric wire they did not receive an electric shock as their feet and tail did not come into contact with the wire. The closure of watering points may not achieve the aims associated with vegetation recovery following the removal of grazing, as kangaroos can travel large distances between watering points and can also have the ability to go for long periods without drinking.
Fertility control Through the use of fertility control techniques, long-term control of kangaroo populations may be possible. Various methods of fertility control have been tested including the use of hormonal contraceptives and immuno- contraception - vaccinating the animal against its own eggs, sperm or reproductive hormones. The use of hormones to inhibit reproduction has generally been found to be successful. With contraceptives such as Levonorgestrel (currently used by human females), has been found to be a suitable long-term contraceptive in Eastern Grey Kangaroos. However, the chemical has been implicated in some side effects associated with the reproductive tract and some metabolic changes. Other contraceptives (e.g. Deslorelin, a non-steroidal contraceptive) have been trailed in female Tammar Wallabies and found to be effective. However, some hormones have the potential to alter social behaviour, including dominance hierarchies, which can influence access to food. The use of contraceptives is currently limited to small populations of kangaroos rather than broad-scale control. As the use of contraceptives is expensive and in some cases cannot be applied without first anaesthetizing the animal. Contraceptives such as Deslorelin will become cheaper and more easily applied if methods can be developed for darting animals from a distance. The use of the immuno-contraception fertility control method has been found to have both practical and ethical issues, and has not been advocated as a fertility control method. An alternative to hormonal or immuno-contraception is surgical sterilisation, however such methods are very expensive, invasive and have been found to be not always effective. Ultrasonic devices Ultrasonic deterrent devices have been designed to protect agricultural properties from kangaroos, however some research has found that ultrasonic devices were ineffective in altering behaviour of kangaroos. Kangaroos exposed to the ultrasonic frequencies, exhibited no changes to their behaviour e.g. vigilance or flight, nor were they deterred from areas where the device was used, which is contrary to the claimed effects of ultrasonic devices. Fencing to exclude kangaroos There are various fence and gate designs which can reduce damage to crops and pastures by excluding kangaroos. Where controlling kangaroo numbers is not the primary objective, kangaroo access gates or stiles can be included in fencing to allow the animals to come and go without causing significant damage to fences. Sloped fencing If kangaroos are unable to crawl through or under a fence, the alternative is to jump over the fence. To be able to jump over a fence kangaroos must get as close as possible to the fence and make an almost vertical jump. Sloped fencing works through angling the fence at an angle of approximately 45 degrees away from the approach of the kangaroo thereby preventing the animals from getting close enough to the top wire of the fence to jump over. Double fencing Double fencing also works on the principle of preventing kangaroos from jumping over the fence through construction of two parallel fences, thus preventing animals from jumping over them. The outside fence is usually much lower than the inner fence. Electric fencing Correctly designed electric fences have been found to exclude kangaroos. The McCutchan fence is one of many designs: the fence is constructed to include 10 wires, 1.8 m high leaning at an angle of 45 degrees away from the approach of the kangaroo with eight plain wires, alternating live and earth wires and two non-electric ('hot') wires at the top. Various other designs similar to the McCutchan fence have been trialled, and have found to be effective in controlling kangaroos, despite being expensive to construct. Predator urine to deter kangaroos Kangaroos have been found to avoid and flee areas where Dingo (Canis dingo) urine was present, where as exposure of kangaroos to Coyote urine, proved novel and kangaroos approached the source of the urine. Kangaroo's avoidance behaviour of historic predators such as the Dingo are usually inherited and then reinforced through experience. It is not known whether over time kangaroos may become accustomed to the odour of Dingo urine and therefore declines in effectiveness of the predator urine may result. Predators Dingoes The Dingo-proof fence protects most of the rangelands' sheep. There is evidence that dingo predation can limit kangaroo populations, primarily through the removal of juveniles, and delaying the recovery of kangaroo numbers after drought. However, the reintroduction of Dingoes to rangeland areas is likely to be unpopular with sheep graziers, because Dingoes often prefer to prey on sheep rather than kangaroos, because sheep are a confined, easier and more accessible prey, and are kept at relatively steady densities. Wedge-tail eagles Wedge-tail Eagles have been found to hunt together to kill adult kangaroos, but their preference is likely to be for smaller animals. Wedge-tail Eagle diets include macropods with 0-67% by the number of items collected in and around Wedge-tailed Eagle nests, but many of these items may be taken as carrion, rather than live individuals. Destruction of animals Destruction of kangaroos by shooting is carried out through a licence system, with non-commercial kangaroo culling accounting for approximately 1% of the animals culled. Commercial harvesting of kangaroos is undertaken by licensed shooters (through the Department for Environment and Natural Resources) on leasehold and freehold land used for agriculture and National Parks, State Forests or in Conservation Reserves. Commercial harvesting is undertaken in Queensland, New South Wales, South Australia and Western Australia. Shooting of kangaroos for commercial harvesting is according to a Code of Practice (developed in conjunction with the RSPCA). Shooters are required to shoot at the head and to use powerful rifles that shoot accurately, resulting in instant death. Private landowners can apply to DENR for a licence to cull a specified number of animals on their land. The kangaroos that are killed are not to be sold but left where they are shot. Kangaroo populations show a variable response to culling depending on the location of the area to be culled. Where rates of immigration of kangaroos is low, culling has been successful. However, where sites have surrounding native vegetation or are on pastoral leases, culling is less successful due to the movement of animals from neighbouring land. Amendments to culling through the targeting of females may be used to maximise success, as culling females reduces the number of new joeys that enter the population. It has been concluded that shooting is the most economical, effective and environmentally friendly means to control large numbers of kangaroos. From an animal welfare perspective shooting is acceptable, but does have potential problems and does have its critics. Bibliography
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Briefing note on Kangaroo Management - II