Terrestrial locomotion imposes high metabolic requirements on bats

SummaryThe evolution of powered flight involved major morphological changes in Chiroptera. Nevertheless, all bats are also capable of crawling on the ground and some are even skilled sprinters. We asked if a highly derived morphology adapted for flapping flight imposes high metabolic requirements on bats when moving on the ground. We measured the metabolic rate during terrestrial locomotion in mastiff bats, Molossus currentium; a species that is both, a fast-flying aerial-hawking bat and an agile crawler on the ground. Metabolic rates of bats averaged 8.0 ± 4.0 ml CO2 min-1 during a one minute period of sprinting at 1.3 ± 0.6 km h-1. With rising average speed, mean metabolic rates increased, reaching peak values that were similar to those of flying conspecifics. Metabolic rates of M. currentium were higher than those of similar-sized rodents under steady-state conditions that sprinted at similar velocities. When M. currentium sprinted at peak velocities its aerobic metabolic rate was 3-5 times higher than those of rodent species running continuously in steady-state condition. Costs of transport (J kg-1 m-1) were more than ten times higher for running than for flying bats. We conclude that at the same speed bats experience higher metabolic rates during short sprints than quadruped mammals during steady-state terrestrial locomotion, yet running bats achieve higher maximal mass-specific aerobic metabolic rates than non-volant mammals such as rodents.