Post-natal growth and breeding biology of the hoary bat (Lasiurus cinereus)

Little information is available on growth rates and reproductive effort in microchiropteran bats that breed in temperate areas, are not colonial, and do not hibernate. We measured growth in individual young of the hoary bat, Lasiurus cinereus, a solitary, foliage-roosting, migratory species, and ass essed growth rate using changes in forearm length. We tested the prediction that growth is slower in this than in other species because of the less st able thermal environment that adults and juveniles experience, Forearm leng th and mass of 1-day-old young ((X) over bar + SE) were 19.11 +/- 0.30 mm a nd 4.73 +/- 0.20 g, respectively. Over 3 years, growth rate of young differ ed, with young growing slowest (1.14 mm/day) during the coldest year and fa stest(1.45 mm/day) during the warmest year. Young were not weaned until 7 w eeks of age and nearly 3 weeks after hedging and continued to gain mass ove r winter. Unlike other species, lactating females did not lose mass through the breeding season. Based on a Levenberg-Marquardt algorithm for nonlinea r regression, the growth constant of young hoary bats (0.083 in females) is less than that documented for most other species breeding in temperate Nor th America. Migratory habits of L cinereus allow adults and young of the ye ar to forage throughout winter and may be associated with slow growth in th is species and production of relatively large litters in species of Lasiuru s in general.