Visual Ecology of Prey Capture in Bearded Dragons

The bearded dragon, Pogona vitticeps is an Australian lizard that is popular in the pet trade in the U.S. and is regularly bred in captivity. They prey upon small fast moving prey. After detecting prey visually they approach rapidly to within a few centimeters and capture it with a rapid launch of the tongue. We filmed prey capture in various situations by a captive bearded dragon in order to assess how they track and judge distance prior to capture. When the lizard was stationary it would initiate prey capture at an average distance of 4.05 centimeters, and then shoot the tongue forward. When attempting to capture the prey while moving, the lunge forward would begin at an average of around 7.32 centimeters and the tongue length when making contact with prey was significantly longer as well. The fact that the distance of the lunge is not always the same implies that they possess a capacity for gauging distance. This lengthening of strike distance and tongue length could also be a signifier of lower confidence due to the movement of the prey. Bearded dragon eye visual fields are largely non-overlapping, but they possess a small region of binocular overlap of the visual field directly in front of them. In order to test for the role of binocular vision in prey capture, we carried out prey-capture trials with one eye covered. In this case both parameters in stationary and moving prey were lengthened considerably and accompanied by a lower success rate in capture attempts. This indicates that binocularity is used in tracking of prey and that distance judgement for capture relies on binocularity too. It must be noted however that prey capture was still possible and relatively successful with one eye covered. This suggests that the lizards are also able to use the extent of focus to judge distance to prey in addition to binocular distance cues.