Behaviour 2019
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The Visual Field of the Bottlenose Dolphin (Tursiops truncatus)
Tabitha S. Gunnars1, Rebecca Milner2, Meghan Barnes2, Krysta Walker2, Charles Abramson1, Jason N. Bruck3. 1Oklahoma State University, Stillwater, OK, United States; 2Dolphin Quest, Sandys Parish, MA 01, Bermuda; 3Stephen F. Austin State University, Nacogdoches, Texas, United States

The field of vision (FOV) of an organism predicts the detection of threats and the localization of resources. In converse, an expansive blind spot, while usually associated with greater binocular vision, can leave animals vulnerable. In whales, we have the unique phenomenon of a predator species with a prey-like eye arrangement. This makes the estimation of the dolphin blind spot difficult from purely anatomical studies and necessitates a psychophysical approach to determine a dynamic FOV. We tested claims that blind spots would occur along the dorsal fin based on boat injuries and that dolphins could not see in the frontal area of their rostrum under what we termed the echolocation replacement hypothesis (ERH) for dolphin vision. Using LED lights attached to a sphere around their heads, where dolphins were trained to vocalize as a light turns on, we mapped the dynamic FOV. We discuss the possibility of the ERH for dolphin anterior vision, as well as the window of posterior vulnerability to ship strikes. Our results have direct implications for researchers working by boat in close proximity to animals as well as researchers developing close approach drones for conservation.