Summary
1. As part of an overall study of the social behavior of the little brown bat, Myotis lucifugus, we compiled the vocal repertoire of this gregarious species in its natural habitat. Ten vocalizations were identified and associated with certain behavioral contexts.
2. Echolocation pulses, although primarily used for orientation, are also available as interindividual communication signals and modified forms are used in several situations such as during near-collisions in flight and the first flights of newly volant young.
3. Nonecholocation calls are used in three main contexts. Agonistic vocalizations appear to take the place of physical aggression and may be used to protect an individual's position within a roost. Two vocalizations emitted in maternal-infant situations appear to contain vocal signatures which are important for individual recognition. During mating, a distinct copulation call given by males likely conveys a male's sexual motivation to a female in the absence of precopulatory displays.
4. The size of the vocal repertoire is comparable to those of some solitary mammals. Behavioral observations indicate that despite the gregarious nature of the species, a simple social system exists and the small repertoire is therefore not surprising.
Methodology
Field work was conducted at two main sites from September to November 1976 and April through October 1977. We observed the behavior of bats during swarming, mating, and hibernation at an abandoned mine in Renfrew County, Ontario, a site used as a hibernaculum by 10,000 to 20,000 M. lucifugus (see Fenton, 1970, for details). Several locations around the Queen's University Biology Station (QUBS) on Lake Opinicon, Leeds County, Ontario, were used during the spring and summer months. Bats using feeding sites over the lake, a nursery colony in an abandoned silo, and three night roosts in two barns were observed and some were also brought into the lab at QUBS to record vocalizations from known individuals, a situation not always possible in the field. We observed the bats through either a Zoomar night vision scope or a GBC 'Total Darkness' television camera using existing light or with the aid of a GE red-ruby 60-W light bulb (wavelength 580-740 nm). In the mine, light filtered through a Kodak Wratten 29 gelatin filter ( > 600 nm) was also used. The TV camera allowed us to make remote observations and at other times we kept as far from the bats as possible in order to minimize disturbance. The use of colored plastic bands (A.C. Hughes, England) attached to the bats' forearms allowed quick identification of the sex-age class of a portion of the population in the mine.