Seasonal wing loading and the ontogeny of flight in Phyllostomus hastatus (Chiroptera: Phyllostomidae)

Abstract

We measured postnatal changes in wing morphology and flight capability in free-ranging Phyllostomus hastatus (Chiroptera: Phyllostomidae). Area of wing, wingspan, and aspect ratio increased until volancy, while wing loading reached its lowest values at and after weaning. Young began to fly in their 7th week, when wing area, aspect ratio, and wingspan had reached 84, 95, and 89%, respectively, of values for adult females. Foraging time increased as young achieved volancy. Estimates of flight 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 constant level at weaning. Thus, wing morphology of young may function to maximize maneuver-ability and minimize energy requirements during the vulnerable period of first flight. Wing loading of adult females fluctuated greatly with seasonal changes in body mass. Wing loading of nonreproductive females, a factor of their greater wing area and lower body mass, was significantly lower than in males. An upper limit on the ability to accomodate increased mass may affect wing morphology in this species.