Prolonged decline in the abundance of wild European rabbits Oryctolagus cuniculus and high immunity level over three years following the arrival of rabbit haemorrhagic disease

A free-living population of European rabbits Oryctolagus cuniculus was moni tored over three years, from 1996 to 1998, following the arrival of rabbit haemorrhagic disease (RHD) in 1995. The survey was based on nocturnal obser vations of individually marked rabbits to determine population size and on blood collection to determine whether rabbits carried RHD antibodies. We di rectly confirmed RHD outbreaks by examination of dead rabbits and detection of RHD virus (RHDV). Only one further recurrence of RHD was detected by th is method, in 1996. Contrary to the initial outbreak, this second occurrenc e did not result in a major decrease in population size. No direct evidence of other outbreaks was detected in 1997 and 1998. However, the sparse data did not enable us to conclude that RHD was absent. Indeed, seroconversions in individual rabbits were noticed throughout the three years and the leve l of population immunity remained high, proving that either RHDV or PHD-lik e viruses were present in the population. The influence of age, year and qu arter on the serological status of the rabbits were analysed using a log-li near model. The selected model showed that the proportion of rabbits with R HD antibodies varied with year and period of the year. Three years after th e first occurrence of RHD, the population had not recovered to its level pr ior to the first outbreak. We assumed that predation by red foxes could be partly responsible for keeping the population low.