The behaviour of wild European rabbits, Oryctolagus cuniculus, in response to predatory and non-predatory mammals and birds was studied in experimental and natural encounters by direct observation and radio-telemetry of free-living individuals and individuals in enclosures. At the primary study site, with heterogenous habitat, rabbits were less gregarious in high than in low cover, were not territorial, had large, overlapping home ranges, and most adults seldom used the available warrens to rest in and as refuges against predators. Predation and myxomatosis caused 92% of all mortality and young rabbits suffered the highest mortality. Adults in groups were more often alert and more likely to detect the observer, but fed less, than lone adults. Rabbits could signal danger to conspecifics, but did not do so when the risk was high to themselves. Flight, screams, and thumping usually alerted rabbits to danger and adults distinguished between warning calls and songs of birds. Rabbits detecting other species responded with 'no response', orientation, crouching, and flight. The degree of response varied with the detection distance, species, suddenness of appearence, speed, altitude, and the direction of approach, location within home range, habitat, experience and/or age of the rabbit, and the behaviour of the other species. Younger rabbits were more likely to flee into warrens than were adults. Covert flight, crouching, and thumping were behaviours of greater selective advantage when shown in scrub than low cover habitats. The flight response appeared to be innate, but was adjusted by direct experience. Learning occurred through direct observation of encounters of conspecifics with other species. There was no cooperation amongst rabbits in groups in the defense against predation. Individuals in groups benefitted from aggregating in numbers through increased detection distances. Females established warrens for the use of young fleeing from danger. This study showed that rabbit groups are of a less social and more aggregative nature than thought and that the defense against predation of this species probably has evolved in scrub habitat.