Changing incidence of parasites in a declining rabbit population

[First paragraph(s)...]
The present paper is a progress report on work undertaken in Hawke's Bav to determine the extent to which changes in the population density of the wild rabbit, Oryctolagus cuniculus (L), are accompanied by changes in the abundance of certain endoparasites. The results are of interest in relation to the suggestion of Whittle (1955) that a host-parasite interaction is the underlying cause of the fluctuations in rabbit abundance which seem to have occurred fairly regularly, with periodicities of 11.5 and 14 years, since at least the year 1900.
Rabbits at Gwavas Forest, some 30 miles south-west of Napier, increased greatly during and immediately after the war, reaching peak numbers about 1948-49. A vigorous control programme was then instituted and the number of rabbits gradually declined, from 1954 onwards the rabbit population was light except for occasional pockets of medium density. Some idea of the magnitude of the decline may be obtained from the fact that 43,000 rabbits were killed m 1948 but only 1,720 in 1955. Samples of rabbits for parasitological examination were collected in the Gwavas district everv month from March, 1950, to March, 1952, and at irregular intervals thereafter. The abundance of the protozoan parasite Eimeria stiedae was assessed on the frequency and severity of lesions in the liver, and E. perforans (an intestinal species) on the number of oocysts recovered from rectal faeces; the size of nematode infestation was determined by counting the worms in aliquot samples of stomach or intestinal contents. Some 5,000 rabbits were examined for E. stiedae and about 1,000 for each of the other parasites.