In Australia, rabbits have high rates of dispersal from the warren where they were born. Understanding this can help with control programs.
Young rabbits disperse to new areas throughout the breeding season. Dispersal rates peak when food becomes scarce and rabbits have to find more food.
Dispersing rabbits have been known to move 20 km or more away from their warrens, often moving from areas with a high density of rabbits to areas of low density.
After dispersal, a rabbit will take up residence in a vacant warren (if one is available) or will shelter in a surface harbour and attempt to join another social group of rabbits.
Where to start control:
For effective long-term rabbit control, efforts should concentrate on destroying source areas. These can be readily identified by the presence of rabbits even during the worst drought or after a myxomatosis or RHDV epidemic. Source areas will all have well-established warrens or ready-made structures that are cool and provide protection from predators.
A source area must also have a good supply of green feed during the cooler seasons. The reason for targeting source areas is that they are the areas where rabbits breed and the birth rate exceeds the death rate.
This leads to an increase in the rabbit population, with the excess rabbits dispersing and continually repopulating the surrounding districts—particularly in good seasons when they can flourish.
The dispersing rabbits are less of a concern than those in the source areas, however, because droughts, disease and predators routinely impact upon them to reduce numbers. It is always new rabbits from source areas that will become the next wave of dispersing rabbits in the coming months or seasons.
Coordinating control:
Rabbit control is best done as a joint exercise involving all land mangers in the district. This may not always be possible, but with landcare groups operating in most areas, and funding often available, it makes sense to talk to other land managers in the district to coordinate efforts. Cost-effective, long-term results can be achieved in rabbit control by following the methods outlined below.
Control methods:
Integrated control
Lanholders should adopt an integrated control approach, incorporating appropriate strategies from those listed below. It is important landholders understand that biological control agents such as myxomatosis and RHDV are not the complete answer to the rabbit problem. It is essential they are incorporated into a management strategy with other control techniques.
RHDV offers landholders a major opportunity to reduce rabbit numbers; however, failure to combine RHDV with other control strategies could cause rabbit immunity to develop (as occurred with myxomatosis).
Destroying a rabbit’s home (e.g. warren) is the most effective method for long-term control. DPI&F has conducted warren ripping trials in Queensland and rabbits fail to re-establish in areas where warrens were ripped properly.
Conventional control methods, such as fumigating, ripping warrens and harbour destruction, are essential for the continued long-term reduction of rabbit numbers.
Warren destruction (ripping):
In areas where rabbits live in warrens, destruction (ripping) is the most effective method of long-term control. Ripping is so successful because warrens can rarely be reopened and rabbits are unable to recolonise these areas. While some older rabbits may remain at ripped sites for a year or two, there will be no younger rabbits to replace these older rabbits once they die out.
Combined with other control methods, ripping can reduce a rabbit population to 1–2% of its original size. To get the best results it is important to chase as many of the rabbits inside the warren as possible. Dogs can be used to drive rabbits into the warren before ripping starts.
The aim of ripping is to completely destroy the warren. It involves using a tractor with a tyned (sharp-pronged) implement—one tyne or many— that rips through the warren and collapses it. Larger tractors and dozers are more appropriate for properties with many warrens as they are able to move faster and rip wider.
Obviously, ripping is not suitable for warrens located underneath buildings or on steep rocky country. In such cases, other methods (poison baiting, releasing virus or fumigating burrows) should instead be used to reduce rabbit numbers. Warrens should then be either filled in or covered to stop rabbits from re-establishing. Burrows can be blocked with small boulders or rocks (see below).
Harbour destruction:
Where there is abundant surface harbour, a high proportion of rabbits may live above ground rather than in underground warrens. Rabbits can make their homes in windrows, dense thickets of shrubs (such as blackberries and lantana) and even in old machinery.
To eliminate these above-ground breeding areas, it may be necessary to:
- burn windrows and log piles
- remove noxious weeds through chemical and physical control
- remove movable objects (such as old machinery) from paddocks.
Sometimes removing harbour can expose warrens underneath. If this happens, the warrens will need to be ripped.
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