The ontogeny of individuality in black-tailed prairie dogs, Cynomys ludovicianus
We examined the ontogeny of individual distinctiveness in time-allocation patterns of black-tailed prairie dogs (Cynomys ludovicianus). All adults and yearlings (n = 112) in the study colony were observed in 14 separate samples, beginning in early April and ending in mid-August. Pups (young of the year, n = 105) were observed in the last 11 of these samples, beginning with their first emergence above ground in late May to early June. Discriminability was determined using a Monte Carlo procedure that randomly selected data from 20 individuals; these data were then entered into a discriminant analysis and this procedure was repeated 100 times. The percent correct classification from these runs was averaged to produce a mean discriminability score. We found that (i) overall, individual pups were discriminable at levels three times higher than that expected by chance alone, (ii) pup discriminability declined significantly over the summer and yearlings had lower discriminability scores than did pups, (iii) average discriminability increased from yearlings to adults and adult values were significantly higher than those for pups, (iv) with the exception of mothers (who had the lowest discriminability values of any group tested), all sex and parental groups of older prairie dogs were significantly more discriminable than were pups, (v) distinctiveness among pups did not appear to be a result of differences between litters, and (vi) measures of behavioral bout lengths proved no better at discriminating individuals than time budgets. The results indicate that the ontogeny of individuality in prairie dog time budgets is not a simple linear function and that discriminability may be constrained by a number of contextual influences.