Initial effects of rabbit haemorrhagic disease on free-living rabbit (Oryctolagus cuniculus) populations in central-western New South Wales

Quarterly spotlight counts of rabbits were conducted at three sites in cent ral-western New South Wales. These counts commenced two years before the ar rival of rabbit haemorrhagic disease (RHD) in the winter of 1996. The exist ing data on quarterly rates of change in rabbit abundance for the three pop ulations provided a unique opportunity to study the effects of RHD on rabbi t demography. Prior to the arrival of RHD, all three populations underwent phases of sequential increase and decrease in each year. On the basis of th ese patterns, RHD had a variable influence on the demography of the three r abbit populations. In 1996-97, the density of two populations declined over an expected period of increase, while at the third site the density increa sed as expected from pre-RHD patterns. Twelve months after their failure to generate expected positive rates of increase the two affected populations had returned to the normal sequence of increases and decreases in density a lthough still at comparatively low numbers.