Economy of Harem Maintenance in the Greater Spear-Nosed Bat, Phyllostomus hastatus

Abstract

To investigate constraints on males associated with maintenance of harems, we used a time-energy approach to explore the relationship between temporal occupancy of roosts and nightly foraging activity in male and female greater spear-nosed bats, Phyllostomus hastatus. Harem males and females differed significantly in frequency and duration of nightly foraging bouts. Harem males spent less time away from their roost at night and departed and returned more frequently than did other members of the harem. Adult females and one subadult male foraged mostly during the first 2–3 h after sunset. Total time spent foraging by harem males, adult females, and a subadult male, averaged 98, 152, and 115 min per night, respectively. On average, harem males engaged in 7.2 randomly spaced foraging bouts per night, compared with 2.1 bouts for harem females and 2.0 bouts for a subadult male. Field metabolic rate, expressed on a mass-specific basis (ml CO2 g−1 h−1), averaged 3.4 ± 0.69 SD for harem males, 3.0 ± 0.85 for adult females, 1.9 ± 0.08 for a subadult male. These values varied predictably but did not differ significantly. Similarly, daily energetic expenditure, expressed on a whole-animal basis (kJ/day), averaged 168.6 ± 32.5 for harem males and 124.9 ± 38.9 for adult females but did not differ significantly. Because harem males allocate less time to nightly foraging activity compared with adult females, males should have more time and energy available for vigilance at the roost and/or the defense of females.