Looking where others are allocating attention can facilitate social interactions by providing information about objects or locations of interest. We asked whether European starlings follow the orientation behaviour of conspecifics owing to their highly gregarious behaviour. Starlings reoriented their attention to follow that of a robot around a barrier more often than when the robot's attention was directed elsewhere. This is the first empirical evidence of reorienting in response to conspecific attention in a songbird. Starlings may use this behaviour to obtain fine-tuned spatial information from conspecifics (e.g. direction of predator approach, spatial location of food patches), enhancing group cohesion.
Summary1. Animals use vision to gather information about their environment and then use that information to make behavioural decisions that affect fitness. They will often move their heads or eyes to inspect areas of interest with their centres of acute vision, such as foveae, to gather high resolution information about potential mates, predation risks, or other aspects of the environment. Few studies to date have been able to accurately determine where laterally eyed animals direct their visual attention and how they use their eyes to gather information. 2. We present a non-invasive 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 eye-tracking experiment with European starlings (Sturnus vulgaris) to test the eye-tracking system, calibration methods and highlight relevant aspects of experimental design. 3. We were able to accurately track the gaze of European starlings with <5 degrees of error. We also found that starlings are more likely to fixate on biologically relevant visual stimuli (e.g. predators and active prey) than simple stimuli (e.g. a dot) in video playbacks. 4. The method presented here can be used to address ecological and evolutionary questions about where animals direct their attention and how they visually inspect mates, food and predators, as well as address management questions about how animals inspect man-made objects. This method can also be used to answer fundamental questions about vision, such as how laterally eyed vertebrates coordinate the use of their eyes laterally and binocularly.
Many bird species are capable of large saccadic eye movements that can result in substantial shifts in gaze direction and complex changes to their visual field orientation. In the absence of visual stimuli, birds make spontaneous saccades that follow an endogenous oculomotor strategy. We used new eye-tracking technology specialized for small birds to study the oculomotor behavior of an open-habitat, groundforaging songbird, the European starling (Sturnus vulgaris). We found that starlings primarily move their eyes along a tilted axis 13.46 deg downwards anteriorly and upwards posteriorly, which differs from the axis parallel to the horizon employed by other species. This tilted axis could enhance foraging and anti-predator strategies while starlings are head-down looking for food, allowing them to direct vision between the open mandibles to visually inspect food items, and above and behind the head to scan areas where predators are more likely to attack. We also found that starlings have neither fully conjugate saccades (as in humans, for example) nor independent saccades (as in chameleons, for example). Rather, they exhibit weakly yoked saccades where the left and right eyes move at the same time but not at the same magnitude. Functionally, weakly yoked saccades may be similar to independent saccades in that they allow the two eyes to concomitantly perform different tasks. The differences between the oculomotor strategies of studied species suggest eye movements play variable but important roles across bird species with different ecological niches.
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