Data on wild giraffe herds have often been interpreted as a random association of individuals, but the extent to which giraffe have a more complex social structure may have been overlooked. The focus of this dissertation is to investigate patterns of social relationships among individual giraffe. Social interaction and association (proximity and nearest neighbor) distributions among 6 female Rothschild's giraffe in a captive herd at the San Diego Wild Animal Park were analyzed to identify and describe patterns of social behavior. The use of a captive herd of giraffe eliminates variance in group membership and allows examination of the distribution of social behavior among individual giraffe of known age, relatedness and life histories. Chi-square tests revealed all three measures were non-randomly distributed, indicating female giraffe had social preferences. These distribution matrices were significantly correlated across four time periods separated by social changes, indicating that preferences may be maintained long-term. Mother-daughter dyads and dyads with large age differences between members interacted and associated the most, a pattern consistent with data from field studies of giraffe and similar to other ungulate species. No dominance relationships were evident among female giraffe; egalitarian social structures of this type are common when groups are based on kinship. Older, multiparous females were significantly more likely to lead groups of giraffe in voluntary movement. These data are consistent with a model of giraffe nursery groups composed of a single mother and her daughters, with siblings dispersing following the death of their mother but remaining in the same home range. The social relationships of giraffe might be mediated by the use of vocalizations below the range of human hearing, allowing the potential for communication over long distances. This study included the first experimental evaluation of the response of a mixed-sex herd of Rothschild's giraffe to playbacks of an infrasonic vocalization. No behavioral changes were observed following playback of the vocalization or of a control signal. Though this lack of response could indicate that giraffe do not communicate using infrasound, it is more likely that high levels of ambient noise or characteristics of the signal or signaler used for playback resulted in the absence of response. Two factors suggest investigation of giraffe infrasound should continue: the subjects produced infrasound as part of social interactions, and responses of giraffe coinciding with mechanical signals suggest giraffe may be able to detect infrasound. While there is no reason to suspect that the patterns of social behavior revealed in this study are artifacts of captivity, field studies designed specifically to examine relationships among individual giraffe are needed to verify these relationships. Genetic studies of wild giraffe could validate the hypothesized social system, and experimental studies of perception and individual recognition could clarify how social relationships are maintained. To keep preferred social partners together, captive animal managers should maintain mother-daughter based groups, moving males among institutions to preserve genetic diversity. In the wild, translocations of giraffe should involve mother-daughter groups, as these groups may be more likely to stay together and remain in the new area.
