OOS 13-4 - Foraging energetics and the redistribution of nutrients by Brazilian free-tailed bats

Tuesday, August 9, 2011: 9:00 AM
16A, Austin Convention Center
Jonathan D. Reichard, Lauren E. Gonzalez, Caitlin M. Casey, Louise C. Allen and Thomas H. Kunz, Center for Ecology and Conservation Biology, Boston University, Boston, MA

Foraging behavior is influenced by energetic costs associated with locomotion and reproduction. For bats, flight is energetically costly and the fitness consequences of foraging inefficiently may be great. In North America, Brazilian free-tailed bats, Tadarida brasiliensis, form very large maternity colonies that forage over large areas. We predicted that this species transports large quantities of energy and nutrients from productive foraging grounds and redistributes energy- and nutrient-rich guano over landscapes and beneath roosts. We estimated nightly energy intake using gravimetric and egesta methods and energy budgets using radiotelemetry during nightly foraging bouts of Brazilian free-tailed bats in south-central Texas. We also quantified energy and nutrient content of guano and defecation rates to test the overall hypothesis that bats redistribute energy and nutrients to ecosystems near their roosts. Finally, we used a greenhouse study to test the effect of guano on growth of three native plant species. Thus, we investigated trade-offs associated with foraging energetics and the role of Brazilian free-tailed bats in supplying remote ecosystems with energy and nutrients by testing three main hypotheses: 1) foraging bats gain mass that increases flight costs; 2) bats redistribute energy and nutrients from foraging areas; and 3) guano deposited over landscapes alters growth of native vegetation.


Radiotagged bats using multiple bouts foraged for a total 363 ± 146 min per night. Mass gained while foraging corresponded with >15% increase in estimated flight cost and total cost of foraging exceeded one-third of a bat’s daily energy intake. Moreover, bats voided over 70% of the mass gained during evening foraging bouts within 3 h of returning to the roost. Thus, night-roosting prior to the beginning of morning feeding permitted bats to begin the second foraging bout with lower body mass and flight costs. Furthermore, Brazilian free-tailed bats at Frio cave, with an estimated colony size of 1,000,000 bats, transport ~3,600,000 kJ of energy in guano to the cave and surrounding area each day. Thus, Brazilian free-tailed bats deposit vast quantities of nutrients and energy, which fuel the subterranean ecosystem and may alter plant growth. However, our greenhouse study produced mixed results depending on the plant species tested and quantity of guano added. Consequently, excessive guano deposited over the landscape may hinder growth of native plants near large maternity colonies. Nevertheless, bats play an important role in gathering and relocating energy and nutrients in these patchy ecosystems.

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