A Comparison of Acquisition Rates for Symbols Used in Relative Numerosity Judgments by Bottlenose Dolphins (Tursiops truncatus): The Visual Modality Versus the Combined Echoic and Visual Modalities


Marie Trone

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Stan Kuczaj

Advisor Department



The numerical competence of human infants and non-human species spans a continuum that includes mathematical operations, counting, number discriminations and numerosity discriminations. Numerosity discriminations occur when different responses are made to nonadjacent quantities of items. Spontaneous numerosity discriminations have been evidenced by human infants, chimpanzees, rhesus monkeys, cotton-top tamarins, lions, crows and meadow voles. Trained numerosity discriminations have been demonstrated by dolphins, orangutans, chimpanzees, rhesus monkeys, squirrel monkeys, cotton-top tamarins, rats, raccoons, crows, pigeons and an African grey parrot. It has been suggested that numerical competence is more robust when elicited through more than one sensory modality. Therefore, two dolphins were trained to discriminate three-dimensional symbols that represented 0, 1, and 5 fish. One dolphin was presented with the symbols underwater such that she could perceive the symbols with echolocation and vision. The other dolphin only had access to the identical symbols in air, such that he should only have been able to perceive the symbols visually. Following training, the dolphins were tested on the 0 vs. 1, 0 vs. 5, and 1 vs. 5 combinations. Neither dolphin had experienced the 1 vs. 5 combination during training. Both dolphins significantly selected the symbol that resulted in receiving the largest quantity over the smallest quantity of fish. Moreover, both dolphins were able to make ordinality judgments on the novel pairing of 1 vs. 5. There was no difference in the rate of symbol acquisition between the two dolphins, despite the fact that one dolphin should have had a perceptual advantage over the other dolphin.