Meeting Abstract
As visual predators, day herons face several challenges while hunting across the air-water interface. One potential challenge is that sun glint off of a reflective water surface, which can cause the visual phenomenon we refer to as glare, may reduce visibility of a terrestrial predator’s aquatic prey. Therefore, we might expect that day herons have evolved behavioral, morphological, and/or physiological adaptations to reduce the likelihood of experiencing glare. One possible behavioral mechanism for reducing the amount of sun glint in a visual field is by orienting away from the sun while foraging. However, at an orientation of 180 degrees to the sun, the heron will cast a shadow directly over its strike zone, and risk alerting the target prey. Thus, we expected to see evidence of herons trading off their own visual needs against the problem of being detected by their prey. We tested the hypothesis that foraging herons orient themselves to the sun in a manner that maximally reduces sun glint while minimizing their own shadow in their strike zone. We recorded body orientations of free-living, foraging Great Blue Herons and Great Egrets (Ardea herodias and Ardea alba) in southern Florida, as well as sun position and sun visibility. Our results indicate that herons are orienting randomly with respect to the sun at all solar elevations, including the lowest ones, when the most sunlight is being reflected at the sea surface. These findings suggest that herons are not compensating for glare behaviorally, and other heron behaviors that are thought to be compensatory for glare may need to be reconsidered.
