AGING BLACK-TAILED PRAIRIE DOGS BY WEIGHT OF EYE LENSES

Eye lenses were collected from black-tailed prairie dogs (Cynomys ludo vicianus) in Billings Co., North Dakota, in 1977, and fixed in 5% form alin. Lenses were dried at 95 degrees C for ca. 96 h to a constant wei ght and weighed to the nearest 0.2 mg. Eye-lens weight of young increa sed rapidly during their 1st summer of life, but increases in weight t apered off in older age classes. Young were readily discernible from y earlings, and yearlings from 2-year-olds. Two-year-olds were sometimes difficult to distinguish from older animals. Mean weight of eye lense s for males was slightly heavier than that for females in all age clas ses, but significantly so only in yearlings. Using weight of eye lense s was a reliable technique for aging young during their 1st summer of life and for separating young, yearlings, and 2-year-olds. For older p rairie dogs, we suggest using other aging methods in conjunction with weight of eye lenses.