Ability of wild rabbit, Oryctolagus cuniculus, to lactate successfully in hot environments explains continued spread in Australia’s monsoonal north

Context: European rabbits evolved in Spain and Portugal and are adapted to winter-rainfall Mediterranean habitats. On introduction into Australia in 1859, wild rabbits quickly colonised similar habitats across the southern two-thirds of the continent. However, over the past 40 years, they have spread further into monsoonal savanna habitats in northern Queensland.Aims: To explain this, we considered adaptive responses of wild rabbits to hot conditions, particularly potential mechanisms for reducing the heat load of lactation, which has been identified as a likely limiting factor.Methods: We analysed data from captive wild rabbits to identify mechanisms that could potentially reduce lactational heat load, and obtained data from shot samples of wild rabbits from northern Queensland to determine which of these might be most important in the field.Key results: Rabbits spread food intake evenly across the 20-day lactation period and under hot conditions, captive wild individuals used body reserves to meet energy requirements for lactation, which is more energy efficient than converting digestible foods to milk.Conclusions: This strategy reduces the heat load of lactation, enabling rabbits to suckle young successfully under hot conditions, but it comes at a cost. Rabbits need extra body reserves before breeding and need to regain those reserves between litters.Implications: The slow spread of rabbits into Australia’s monsoonal savannas is likely to continue, given the rabbit’s reproductive flexibility and further natural selection for breeding in this environment