Abstract
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.
Highlights
Title Responses to Familiar and Unfamiliar Humans by Belugas (Delphinapterus leucas), Bottlenose Dolphins (Tursiops truncatus), & Pacific White-Sided Dolphins (Lagenorhynchus obliquidens): A Replication and Extension
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
When overall gaze durations were averaged across all three conditions and examined for species differences in attention, it appeared that bottlenose dolphins gazed the longest at stimuli (M = 9.6 s, SD = 2.3 s) followed by belugas (M = 8.1 s, SD = 5.4 s) and lags with the shortest overall gaze duration (M = 1.3 s, SD = 0.6 s)
Summary
Title Responses to Familiar and Unfamiliar Humans by Belugas (Delphinapterus leucas), Bottlenose Dolphins (Tursiops truncatus), & Pacific White-Sided Dolphins (Lagenorhynchus obliquidens): A Replication and Extension. Responses to Familiar and Unfamiliar Humans by Belugas (Delphinapterus leucas), Bottlenose Dolphins (Tursiops truncatus), & Pacific White-Sided Dolphins (Lagenorhynchus obliquidens): A Replication and Extension. 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 indicated that the cetaceans discriminated between unfamiliar and familiar humans and preferred active humans. When human faces were presented in the left-eye field of vision, participants responded more rapidly than when compared to the right-eye field of vision (Ellis, Shepherd, & Davies, 1979) This example of lateralized visual processing suggests that the ability to recognize conspecifics during social interactions may be hemispheric-specific. A broad range of taxa have demonstrated such hemispheric lateralization, including domesticated birds, fish (reviewed by Bisazza et al, 1998; Johnsson, 1997), crustaceans (Karavanich & Atema, 1998), amphibians (reviewed by Bisazza et al, 1998), reptiles (reviewed by Bisazza et al, 1998), birds (Wilkinson, Specht, & Huber, 2010), and mammals (Kendrick, Atkins, Hinton, Heavens, & Keverne, 1996; Rosa Salva, Regolin, Mascalzoni, & Vallortigara, 2012; Tibbetts & Dale, 2007)
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