A Comparison of three Methods for Determining the Age of Black-Tailed Jackrabbits

As part of a 5½-year ecological study, 47 jackrabbits of known ages were reared in the laboratory and killed at different intervals to establish a growth curve based on the dried weights of the lenses. The base point of the curve was established from weights of lenses taken from hares removed from females during caesarian sections and designated as zero days old. Lenses increased in weight with the age of the animal, and the ages of hares could be accurately determined up to 650 days, the age of the oldest animal killed. The epiphyseal-closure technique for determining ages was used on 2,605 humeri from hares taken in monthly kill samples. The hares were separated into 3 age-classes on the basis of the degree of closure. Weekly measurements on the hind feet and ears were taken, and the age of young hares to 12 and 14 weeks could be accurately determined on the bases of the lengths of hind feet and ears.