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In humans, individuals recognize other individuals by numerous types of independent information, such as the quality of the voice, appearance of the face, smell, gait, and posture. Humans also have integrated memories of others--that is, in response to a face or a voice the individual is recognized by name and other information about that individual is remembered. In many nonhuman species, individual recognition also occurs. Although observational studies suggest that individuals of some nonhuman species may be able to use several different cues for individual recognition, little experimental proof for this is available. Golden hamsters have at least 5 individually distinctive odors and they develop integrated, multiodor memories (concepts) of familiar individuals, as shown by across-odor habituation experiments. Little is known, however, about the conditions that are necessary to develop such integrated memories. In these experiments we investigated what kinds of experiences were necessary for male hamsters to develop multiodor memories of females. The results show that exposure to all of the odors of another individual was not sufficient to develop such multiodor memories but that physical contact between the subjects and stimulus animals was necessary. Multiodor representations were developed after interactions with anesthetized individuals, confirming the finding that physical contact was important but also showing that interaction with an awake, behaving individual was not necessary to form multiodor representations of other individuals. We are not aware of experimental proof for integrated, multicomponant memories in any other nonhuman species. Keywords: individual recognition, hamster, odors, memory, animal cognition

In this investigation, the authors used habituation techniques to explore similarities and differences in the qualities of individual odors from hamsters. In Experiment 1, male Turkish hamsters (Mesocricetus brandti) treated flank-gland odors of 2 males from I litter as similar compared with the odor of a male from another litter, whether the odor donors were familiar or unfamiliar. At the same time, the Turkish hamsters discriminated between the subtle differences in the individual odors of their familiar brothers. In Experiment 2, male Turkish and golden hamsters (Mesocricetus auratus) treated the flank-gland odors of 2 unfamiliar, unrelated conspecifics as similar compared with the flank odor of a heterospecific individual. The results suggest that similarities in individual odors are related to genetic similarity of the odor donors. These similarities could provide a basis for different types of social recognition, including kin and species recognition.

Hamsters preferentially remember or value the top scent of a scent over-mark. What cues do they use to do this? Using habituation-discrimination techniques, we exposed male golden hamsters (Mesocricetus auratus) on 3 to 4 trials to genital over-marks from 2 females and then tested subjects for their familiarity with these 2 scents compared with that of a novel female's secretion. Preferential memory for 1 of the 2 individuals' scents did not occur if the 2 marks did not overlap or did not overlap but differed in age, but it did occur if a region of overlap existed or 1 mark apparently occluded another (but did not overlap it). Thus, hamsters use regions of overlap and the spatial configuration of scents to evaluate over-marks. These phenomena constitute evidence for previously unsuspected perceptual abilities, including olfactory scene analysis, which is analogous to visual and auditory scene analysis.

Odor-elicited scent marking is common among mammals, but the proximate causes of marking are not well understood. Scent marking by female hamsters in response to 8 different male odors was investigated. Two odors (flank, mouth) increased flank marking and 2 (flank, rump) increased vaginal marking; in the latter case the effects of flank and rump odors were additive. Two odors (feces, urine) decreased flank marking but did not affect vaginal marking; other odors (foot, ear, ano-genital) had no influence on either scent-marking behavior. Results show that scent marking by females is influenced by a limited number of male odors, suggesting specific effects of particular odors. Classes of information (such as sexual identity) were not relevant causes of scent marking, as some odors containing such information were effective but others were not.

The memory of hamsters (Mesocricetus auratus) for the flank scent of other male hamsters was investigated in a series of habituation experiments. In 2 types of habituation tasks (Experiments 1 and 2), male hamsters habituated to the flank scent of 1 male and then increased their level of investigation to that of a novel male; similar results were obtained when the intervals between trials ranged from 1 s to 2 days. When the test trial was 10 or 21 days after habituation (Experiment 3), males discriminated between familiar and novel flank scents at 10 days but not at 21 days. The results demonstrate recognition of familiar and unfamiliar individual odors and excellent memory for these differences. Habituation techniques yield extremely robust results and may be useful for investigations of other aspects of individual signatures.