Age determination in the red fox (Vulpes vulpes L.) from tooth cementum lines.

Abstract

The use of incremental lines in tooth cementum as an indicator of animal age was evaluated for red foxes (Vulpes vulpes). We compared cementum line counts with the known age or known minimum age of 23 individuals from southern central England (1985-1987) and central Wales (1973-1980). Age estimates made from decalcified stained sections were correct for 6 out of 9 foxes of known age tagged as cubs, and equal to or above the known minimum age for 20 out of 23 foxes. Two incorrect estimates were one year below actual known age. Against a background of similar analyses by other authors, we conclude that this is a satisfactory basis for general age estimation.
Age estimates made from undecalcified sections viewed under polarised light were less reliable: of 19 sections examined, 10 led to age estimates lower than the known age or known minimum age by up to 3 years. This is clearly either a less reliable or a less readily learned technique.
To determine when cementum lines are first formed in young foxes, we used cementum lines to estimate the age of 121 foxes from two rural sites in southern England. To distinguish young-of-the-year from yearlings born the previous year, we used the lower jaw length and the degree of occlusion of the canine pulp cavity: lower jaw growth was complete at 7 to 11 months and pulp cavity occlusion reached asymptotic levels at 15 to 18 months. By comparing foxes from these two age classes (and which therefore showed 0 or 1 cementum line), it was shown that the first dark-staining cementum line appeared in tooth cementum during January to March of the year following birth. In foxes at this latitude this coincides with the mating season. We discuss the possibilities that reproduction causes cementum line formation in foxes, and that exceptions may therefore be of importance in population studies.
The age structures of the samples from two rural fox populations are presented (n = 40 for Dorset, n = 81 for Salisbury Plain). Although these differ significantly, with a higher representation of older adults in the less intensively controlled population (60 % of adult foxes from the Dorset site were more than 2 years old, compared with 15 % from Salisbury Plain), we are cautious in attributing the difference solely to differences in management.