The influence of host age in parasitism of wild rabbits

[First paragraph(s)...]
Host age has an important influence on the incidence of rabbit parasites, but the nature of the relationship is different for each parasite. This is shown in the figure, where the paunched weight is used as an index of host age. Smaller weight groups have been used for full-grown rabbits than for young ones, and two different scales have been employed, that for the young rabbits being the smaller. This has been done in order to make the horizontal scale more representative of time by minimising the effect of the more rapid increment of weight in the young rabbits.
Paunched weight provides a reliable indication of age in young rabbits up to a limit of approximately four months, but recent work by the Animal Ecology Section on the sequence of fusion of the epiphyses of the bones allows age determination to be extended beyond this limit. These techniques were not available when the present material was collected, but the recent work is relevant in that it suggests that paunched weight may be used as a means of dividing a sample of full-grown rabbits into groups of increasing mean age, although it is of no value in assessing the age of an individual rabbit.