===================================================================== Body length Condylo-basilar Weight minus tail length Age --------------------------------------------------------------------- Six males 32.67 gms. 106.16 mm. 23.78 mm. 9.67 wks. (30-36) (96-116) (23.2-24.4) (8-12) Four females 29.0 gms. 100.25 mm. 23.45 mm. 10.5 wks. (28-30) (98-102) (23.5-23.8) (8-12) Ten voles 31.2 gms. 103.8 mm. 23.73 mm. 10.0 wks. (28-36) (96-116) (23.2-24.4) (8-12) --------------------------------------------------------------------- The mean age of the ten voles molting was ten weeks (8-12). Six males averaged 9.67 weeks, almost a week younger than four females, who averaged 10.5 weeks. The difference in age at time of molting between the sexes was not significant. Differences between the sexes in other characteristics to be described also lacked significance. Mean weights at the time of molting were: males, 32.67 gms. (30-36); females, 29.0 gms. (28-30); and all individuals, 31.2 gms. (28-36). Because a piece of the tail of each vole had been removed in marking, the total length of the voles could not be determined. Body length, excluding tail, was used. Howell (1924:986) found this measurement subject to less individual variation than total length and thought body length was probably a better indicator of age. Mean body length at the time of molting was 103.8 mm. (96-116). Males averaged longer than females and were also more variable. The mean body length of males was 106.16 mm. (96-116) and that of females was 100.25 mm. (98-102). Of the subadults showing no signs of molting, none was above the mean age of molting. Twenty-five per cent of them were longer and heavier than the mean length and weight of those that were molting. Of the 20 adults in the series, one was below the mean weight of molting and one was shorter than the mean length of molting. When Howell (_op. cit._:1014) studied skulls of _Microtus montanus_ he found that the condylobasilar length was the most satisfactory means for arranging his series of specimens according to their age. When the skulls of my series were arranged according to their age (as determined from trapping records) the graph of the condylobasilar lengths showed a clear, though not perfect, relationship to age (Fig. 13). No separation of sexes was made because the sample did not permit it. In Fig. 13 graphs of weight, as determined in the field, and of length (excluding tail) also were included because they are the most easily measured characters of live voles. The graphs indicate individual variation in these characters which limits their usefulness in determining age.