Meeting Abstract
Animals use vision to gather information about their environment, and then use that information to make behavioral decisions that affect fitness. They will often move their heads or eyes to inspect areas of interest with their centers of acute vision, such as foveae, to gather high-resolution information about potential mates and predation risks. But, few studies to date accurately determine where laterally eyed animals direct their visual attention and how they use their eyes to gather information. Therefore, we developed an eye-tracking system that can simultaneously track the gaze of two eyes. This is particularly useful for studying animals with laterally placed eyes (most vertebrates) where the two eyes are viewing different images. This system can also accommodate comparative studies using animals of varying size, including small animals that are not frequently used in eye-tracking studies due to constraints of existing eye-tracking systems. We conducted an experiment to test the accuracy of the system and to define eye movement patterns in European starlings (Sturnus vulgaris). We were able to accurately track the gaze of starlings with less than 5º of error. Starlings primarily moved their eyes along an axis 17.8º (± 2.9º) off horizontal, such that they look forward and down, as well as up and back. This axis could aid the ground foraging starling in finding food on the ground and in detecting aerial predators approaching from behind. Starlings exhibited a spectrum of yoked and non-yoked eye movements, including the ability to fully converge their eyes forward, but could not simultaneously diverge their eyes to the extent predicted by the movements of a single eye. Therefore, starlings have a more limited ability to reduce the blind area behind the head than previously thought.
