Behavior and communication modes were studied in captive <u>Monodelphis domestica</u>, a small solitary, nocturnal, omnivorous marsupial in the family Didelphidae. The social biology was examined to evaluate the importance of visual, olfactory, auditory, and tactile communication. Social contexts were compared in 124 encounters of 30 min each. An ethogram was developed containing 74 behaviors which sorted into 9 major behavioral categories: grooming and resting, exploration, attention, scent marking, vocalizations, social contact, aggression, retreat, and sexual. Solitary <u>Monodelphis</u> explored, groomed, and scent marked. Familiar male-female pairs displayed less aggression than unfamiliar male-female pairs. Non-estrous females aggressively repelled males and exhibited much dominance related behavior, but male-male pairs were the most agonistic. Seven scent marking modes were identified which functioned to communicate individual identity and sexual advertisement. Males could distinguish sex and estrous condition of conspecific urine donors by olfaction. Dig perineal dragging, lateral side rubbing, and hip rubbing were unique to <u>Monodelphis</u>. Tongue protrusion was observed and may be related to vomeronasal organ function. Four principal agonistic vocalizations were used while one, clicking, was observed only in male sexual behavior and submissive contexts by both sexes. A chittering vocalization is described. Social contact behaviors included approaches and directed sniffs. Males sniffed female cloacal regions who in turn sniffed the ma1es’ sides and abdomens. Dominance-subordinance relationships were characterized. Behavior of close relatives <u>Didelphis</u> and <u>Marmosa</u> was similar, but some behaviors were unique to <u>Monodelphis</u>. / Master of Science / incomplete_metadata