International Journal of Comparative Psychology

Previous research has documented that cetaceans can discriminate between humans, but the process used to categorize humans still remains unclear.  The goal of the present study was to replicate and extend previous work on the discrimination between familiar and unfamiliar humans by three species of cetaceans.  The current study manipulated the familiarity and activity level of humans presented to 12 belugas ( Delphinapterus leucas ) housed between two facilities, five bottlenose dolphins ( Tursiops truncatus ), and six Pacific white-sided dolphins ( Lagenorhynchus obliquidens ) during free-swim conditions.  Two measures of discrimination were coded from video recordings of each trial: lateralized visual processing and gaze duration.  No clear lateralization effects emerged at the species level, primarily due to extensive individual variability.  The results also indicated that activity level influenced gaze durations across species, and for some individuals, the interaction between human familiarity and activity level influenced gaze durations and eye preferences.  Unexpectedly, bottlenose dolphins had longer gaze durations for familiar humans whereas belugas and Pacific white-sided dolphins had longer gaze durations for unfamiliar humans.  All three groups displayed longer gaze durations for active humans as compared to neutral humans, and belugas and bottlenose dolphins had significantly longer gaze durations than Pacific white-sided dolphins.  These results indicate that the cetaceans can discriminate between unfamiliar and familiar humans and preferred active humans.  However, discrimination of humans via lateralized visual processing did not appear at the group level, but rather at the individual level which countered previous research.  This study is discussed within the contexts of attention and individual differences across animals of different species.