My own studies of live weasels in nature indicate that in the season when females are attending young which are half grown, or larger, the adult male weasels live singly in dens of their own, separate and apart from the females and their young (Hamilton, 1933:328, records adult males living with the female and her young, but possibly this was when the young were less than half grown). Perhaps these males at that time travel no farther than is necessary to obtain food for themselves. Females, at this time, forage not only to meet their own needs, but for food to supply their young as well. At this time, in May and June, as may be seen from table no. 2, almost as many adult females as adult males _are_ caught. The reason why only relatively more females than in other months, instead of actually more females than males, are caught at this time probably is that the adult males also are extraordinarily active at this time because they are in breeding condition. Perhaps the explanation in part is to be found in the lesser weight of the female (approximately half of the male's weight) which, as indicated above, permits her to step on the pan of a steel trap without springing it whereas the heavier male does spring the trap and as a consequence is caught. Hamilton (1933:299-300), who mentions this selective factor, found an equal number of males and females in the three newly born litters that came under his observation. TABLE 2 Specimens of _Mustela frenata_ (north of the range of _M. f. frenata_) arranged by sex and under each sex by age KEY: A: adult [M] B: [M] ad., % of total adults C: subadult [M] D: young [M] E: juvenal [M] F: total number of [M] G: [M] % of total H: adult [F] I: [F] ad., % of total adults J: subadult [F] K: young [F] L: juvenal [F] M: total number of [F] N: [F], % of total O: total number of [M] and [F] P: total number of adults, [M] and [F]