SEASONAL WING LOADING AND THE ONTOGENY OF FLIGHT IN PHYLLOSTOMUS-HASTATUS (CHIROPTERA, PHYLLOSTOMIDAE)

We measured postnatal changes in wing morphology and flight capability in free-ranging Phyllostomus hastatus (Chiroptera: Phyllostomidae). A rea of wing, wingspan, and aspect ratio increased until volancy, while wing loading reached its lowest values at and after weaning. Young be gan to fly in their 7th week, when wing area, aspect ratio, and wingsp an had reached 84, 95, and 89%, respectively, of values for adult fema les. Foraging time increased as young achieved volancy. Estimates of f light speed and power requirements from theoretical predictions yield flight speeds that are lowest around weaning, power requirements that increase consistently, and a cost of transport that decreases to a con stant level at weaning. Thus, wing morphology of young may function to maximize maneuverability and minimize energy requirements during the vulnerable period of first flight. Wing loading of adult females fluct uated greatly with seasonal changes in body mass. Wing loading of nonr eproductive females, a factor of their greater wing area and lower bod y mass, was significantly lower than in males. An upper limit on the a bility to accomodate increased mass may affect wing morphology in this species.