Under good conditions, rabbits can breed all year round but breeding may be limited by two main factors:
- Female rabbits require a diet of at least 14% protein to trigger breeding. (Short fresh green grass and herbage usually has a high protein content.)
- Lactating female rabbits need a warren temperature under 28 °C. (A higher temperature lowers the milk output of the lactating female so the young have less chance of survival.)
Rabbits mostly breed during the cooler months of the year but this depends on seasonal conditions. In a good season, five to six litters are possible; breeding may stop completely in dry conditions.
In areas where warren temperatures are above 27 °C and rain falls predominantly in summer, pasture quality may be poor and heat stress can reduce the milk output of lactating females so their young may have less chance of survival.
This may help to explain why rabbits have not spread in large numbers into the northern parts of Queensland. Rabbits reach sexual maturity at three to four months of age. The gestation period is 28–30 days, and the female is able to mate again within hours of giving birth.
Depending on the amount and quality of food available, a female can produce an average of 11 young per year in marginal areas and as many as 25 or more in favourable areas. Once mature, a young rabbit can travel long distances (up to 20 km) to find a new home.
In newly colonised areas, they will live in a shallow hollow within long vegetation or under fallen timber such as windrows and log piles.
The rabbit warren:
Rabbits prefer to live in warrens for protection from predators and extremes of temperature. However, they will survive in above-ground harbours such as logs, windrows and dense thickets of scrub, such as blackberry and lantana. In newly colonised areas without warrens rabbits tend to live in what is called a ‘scrape’ (or ‘squat’) under fallen timber and in long grass.
Without protection from the elements, rabbits are not able to breed successfully. The newborn rabbit has little or no hair, making it very susceptible to temperature extremes. With warren protection, rabbits are able to produce up to 10 kittens per litter compared with only four per litter when forced to breed in above-ground harbours.
If a warren is available, the number of litters produced per year will also be more than if the rabbit is breeding above ground. Rabbits do not find it easy to dig new warrens. They prefer to take over the burrows of native animals such as burrowing bettongs and bilbies.
The native animals are eff ectively excluded from their burrows and the rabbits subsequently form their own warren. This ready-made underground breeding area proved to be a great resource for rabbits when they colonised Queensland.
The size of a warren depends on the soil type. Typically, warrens can be around two metres deep, although warrens in sandy soils are more likely to be smaller and have fewer underground interconnections than warrens in hard soils.
This is because it is easier for rabbits to start a new warren in sandy soil but in harder, clay-type soils it is easier to extend an existing warren. On average, one warren will have 3 to 15 entrances, with each active entrance likely to house two adult rabbits.
Most rabbits will remain within 300 m of their warren, though this will vary depending on the season and the availability of water. In severe drought, rabbits have been recorded moving 1.5 km to drink. Rabbits will generally spend most of the night above ground feeding and remain in the safety of the warren during the day.
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