Postnatal growth and age estimation in the Indian pygmy bat Pipistrellus mimus

Abstract

The Indian pygmy bat Pipistrellus mimus produced two young per litter, which were altricial at birth. Empirical growth curves were derived by measuring length of forearm, body mass, and length of the total gap of the fourth metacarpal-phalangeal joint. Length of forearm and body mass followed a linear pattern of growth until day 20 and subsequently reached stability. The length of the total gap of the metacarpal-phalangeal joint showed a linear increase up to 20 days, followed by a linear decrease until ca. 80 days when it closed. A quantitative method of estimation of age was derived from values of length of forearm and length of the total gap of the fourth metacarpal-phalangeal joint during the preflight (first 20 days) and postflight stages, respectively. Width of the 95% confidence level was ±0.6 days at a mean length of forearm of 15.1 mm, and it was ±0.9 days at a mean length of the total gap of the fourth metacarpal-phalangeal joint of 2.0 mm. Initiation of flight occurred 21 days after birth. At 33 days of age, young were able to forage on their own. Females experienced their first parturition at the mean age of 112 days. Females of P. mimus apparently attains sexual maturity within 2 months after birth, which may be the youngest age for sexual maturity in a bat.