Most male Richardson's ground squirrels do not survive their first year, and those that do have less than a 50% chance of surviving each succeeding year. Thus, reaching three years of age is very rare for males. Females have higher survival and, therefore, greater longevity, with many living three or four years and a few surviving as much as five or six years. data
This difference in life span reflects
the different life-history strategies adopted by the two sexes. Males
opt for the high-risk strategy of dispersing, whereas females are more
conservative and remain near their natal home range. (see Dispersal)
Males also undergo more extreme pressures during the mating season due
to intrasexual competition for access to females. (see Reproductive
Behaviour) This difference in mortality results in a skewed sex
ratio among adults, with 3 to 5 times as many adult females as adult males.
(see Reproductive Physiology)