Abstract
I determined the age of sexual maturity in Japanese giant flying squirrels, Petaurista leucogenys. The degree of testicular development was estimated in 25 males 224 times during eight years. The scrotum began to extend at the age of 7.5-8.5 months, and was slightly swollen in males 8-13 months old. Testes of 1⁄2-3⁄4 size were observed in males from 14 months onward. By the mating season when they were 21-22 months old, the proportion with full-sized testes was 57% of the males. All five males of 27-28 months of age had full-sized testes. One 22 month-old male and one 27 month-old were observed copulating. Summer-born males had slightly faster developing testes than spring-born males. None of 19 young females were observed in estrus. The attainment of sexual maturity in males at 21-22 months of age seems very late as the intermediate-sized rodents. It is suggested that mothers allow their young to remain with them for 1-1.5 years until they become sexually mature in order to increase the survival rate of their young, thereby compensating for their small litter sizes of one or two.
