(Uploaded by Plazi for the Bat Literature Project) We analyzed infrared video recordings from a maternity roost in southwestern Arizona to determine social behavior and time and activity budgets of adult Leptonycteris curasoae (Chiroptera: Phyllostomidae) for 2 weeks late in the nursing period. Between 2000 and 0330 h, females nursed their young an average of two times for a total of ca. 52 min. Females nursed only their own babies; they occasionally interacted with other young and adults. most frequently by touching noses. Adults returned to and left their young independently of each other, not in synchronized fashion. Between 0500 and 1900 h, adults seldom interacted, although they were clustered tightly. Young were in a nursing position, presumably nursing, ca. 50% of the time. Adults never appeared to sleep and spent 74% of the day quietly alert and 24% grooming themselves. We observed no cooperative behavior such as allogrooming, communal nursing, or sharing of food at any time. We suggest that absence of stable associations of adults caused by long-:-distance migration and occasional changes in roosting sites has prevented evolution of overtly cooperative behavior in dayroosts of L. curasoae.