The development of flight, foraging, and echolocation in the little brown bat (Myotis lucifugus)

Abstract

1. Two colonies of little brown bats,Myotis lucifugus (Vespertilionidae), were studied for two summers. The young could not perform practice flights within the buildings where they roosted. Young of estimated relative ages and adults were light-tagged, released, and tracked to determine the development of flying skills and foraging behavior. Orientation sounds were observed and tape-recorded. 2. The earliest flights at ca. 19–20 days of age were usually relatively brief (a few tens of seconds or less) but still remarkable considering the absence of practice. The young at first emerged after adults had left to forage, avoided entering acoustically complex habitats, flew slowly within about 50 m of the roost, and made frequent, awkward landings. They avoided other flying bats and did not pursue insects. More time was spent in rest than flight. 3. Slightly older young, beginning at ca. 22–23 days, gradually increased their flight distance and duration (Table 1) and began to hunt insects in clearings or at the forest edge. Some adopted a ‘flycatcher’ hunting style at this time. They still avoided flying conspecifics. 4. The final phase of development began at about days 24–27 and may last 2 weeks or more. It involved virtually continual flight, insect pursuits, and maneuvers that became indistinguishable from those of adults, and also gradual integration with the adults during emergence, flight along traditional routes, and foraging. 5. The echolocation sounds of young of known and estimated relative ages were recorded in the field, a flight cage, or large room. Again, development was rapid. Landing buzzes always occurred, even in the first flight, although the progressive changes in frequency were sometimes not as uniform as in adults. 6. The pulses during all phases of early flight were of lower frequency than in adults. Those emitted during cruise and approach phases were frequently paired. There is possible ontogenetic and phylogenetic significance to this pairing. Within a few days, the pairing disappeared and within ca. 1 week all echolocation parameters became similar to those of adults (Fig. 1; Table 2).