Robab Mehdizadeh, Hojjat Eghbali, and Mozafar Sharifi (2018) We simultaneously monitored postnatal growth and vocalization development in a free living population of the long-fingered bat, Myotis capaccinii, in a maternity colony in the Mahidasht cave, western Iran. Length of forearm and body mass of 1-day-old neonates averaged 19.59 ± 1.23 mm and 3.59 ± 0.23 g and followed linear pattern of growth at mean growth rates of 0.74 mm/day and 0.15 g/day until 28 days of age, after which is increased slowly. A similar nonlinear growth pattern was found for ten wing characteristics (wingspan, wing area, handwing length, handwing area, armwing length, armwing area, aspect ratio, wing loading, tip length ratio, and tip area ratio). However, postnatal growth followed a two phase linear pattern of increase-decrease for the epiphyseal-phalangeal gap and decrease- increase for wing loading. At birth, infant bats produced low, short frequency sonar and oral calls in isolation before they could open their eyes. Isolation calls obtained at age 1-4 days old from M. capaccinii pups were frequency modulated shallow calls with longer duration (7.54 ± 1.83 ms) and lower peak frequency (20.07 ± 0.89 kHz) compared to adult female calls (2.35 ± 0.75 ms and 54.02 ± 4.34 kHz). During days 12-16, calls began to resemble adult echolocation calls. Duration of calls increased slightly before 7 days old and then gradually decreased. The peak, start and end frequencies of spontaneous calls increased with age. When the juvenile bats started foraging outside the cave, they only omitted nasal FM calls with 1-2 harmonics. Comparing postnatal changes in body and wing characteristics with those of vocalization, we found that the most positive correlation was between body (forearm length and body mass) and wing features (wing area, wingspan, handwing area, armwing area and aspect ratio) and call parameters (peak, start and end frequency), while wing loading had a significant negative correlation with the call parameters.