Identification
The typical European rabbit is grey-brown with a pale belly. Black or ginger forms are not uncommon, though they represent a small proportion of the population; white rabbits are rarely seen in the wild. In WA adult wild rabbits weigh from around 1200-2250g.
Behaviour
Rabbits are largely nocturnal animals, emerging from shelter in the late afternoon and retreating early in the morning. They avoid high temperatures and predators by living in burrows or in the shelter of dense scrub or fallen timber.
During the winter breeding season, rabbits live in small social groups that tend to break down in summer when breeding ceases. A large warren may contain several groups. Each social group has its own territory, which it actively defends against intruders. Members mark their territory on logs, grass or other objects with faeces, urine and secretions from a gland beneath their chins. Dominant males (bucks) will also use dung piles to mark their territories. Within each group there is a strict social hierarchy. High-ranking females (does) breed more successfully than lower ranking animals. Dominant males father more offspring than subordinate animals.
Why rabbits have succeeded in Western Australia
Rabbits evolved in the western Mediterranean region, which has a cool wet winter and hot dry summer. This is similar to the climate of the south-west of the state. Rabbits can produce relatively large numbers of offspring, which allows them to take advantage of favourable conditions and to colonise or recolonise areas quickly.
Rabbits are best suited to districts with a long winter, which allows a lengthy breeding season. The biggest populations occur where areas of uncleared scrub, or other suitable cover, are interspersed with improved pastures. These conditions combine the advantages of both high quality refuge areas and food resources. Remnant vegetation in the south-west of WA offers considerable complexity and protection so that rabbits from these areas have less reliance on warrens than in other parts of Australia. Warrens and/or short breeding burrows (stops) are still required for successful reproduction.
Reproduction
The main breeding season of rabbits in the south-west extends from about May to November depending on availability of suitable green feed. It is usually shorter in other areas of the State. The percentage of adult females that are pregnant rises steadily through the breeding season to nearly 100% in July and August. Later, the pregnancy rate falls, as does the average litter size. While breeding virtually ceases when pastures dry off, in the south-west, a small proportion of females can be pregnant in most months. Where favourable conditions for breeding persist, a single doe may produce up to 30 kittens in six or seven litters a year.
Female rabbits usually conceive their first litters shortly after the first autumn rain, thus ensuring the maximum numbers of litters are born while green feed is available. Gestation lasts about 30 days.
In many rabbit populations, the high reproductive rate can be offset by a 60-70% death rate amongst kittens up to a month old. The mortality of kittens born late in the year may rise to nearly 100%, due mainly to lack of suitable feed. Climatic factors, predators and diseases are the main causes of natural mortality. As kittens become older, their survival rate improves. Once they reach adult weight their chances of survival are good. Adult rabbits have an average life expectancy of two to five years.
Damage
Rabbits compete directly with livestock and many native animals for food. It has been estimated that eight rabbits eat as much as one sheep. However, unlike sheep, which graze over the entire paddock, rabbit grazing tends to be concentrated near refuge areas. This can result in very severe localised degradation of both pasture and bush reserves, and significant soil erosion.
Rabbits graze plants closer to the ground than livestock, often killing germinating clover seedlings, preventing good clover establishment. Rabbits may overgraze perennial grasses during summer, even eliminating them from a paddock. The pasture is then more likely to be invaded by weeds, and can become more prone to erosion.
Rabbits do considerable harm to the natural environment and the detrimental impact of rabbits on the regeneration of native plants is well recognised. In many rangeland areas, as few as four rabbits per hectare can prevent the regeneration of native plants, for example, some Acacia species. During drought rabbits can strip bark from shrubs and trees. This increased grazing pressure often results in the loss of vegetation cover, leading to soil erosion. The digging by rabbits to make warrens may also cause soil erosion and tree losses.