Barn owls have a pretty tough job: in near-darkness, they need to catch at least two little critters a day to feed themselves, and about 20 a day if they have offspring. Since the stakes are so high, the selective pressure acting on these birds' vision is quite intense. Last week's PNAS reports that owls exhibit some of the same visual recognition patterns that humans do, despite very different visual systems.

Primates use "orientation saliency" to quickly pick out items in our surroundings that are new, dangerous, or just don't belong. Simply put, if several objects in your visual field are oriented in one direction, your eye will be drawn to the one object that goes the opposite way. Because this process might be useful for predatory owls, researchers wondered if barn owls would exhibit orientation saliency as well.

To answer this question, the scientists attached "the OwlCam," a tiny wireless camera weighing just 5.5 grams, to the heads of two barn owls. Since barn owls don’t move their eyes much, instead relying on head motion to change their gaze, researchers watching the footage could get a good idea of what, exactly, the owl was focusing on in its field of view.

Each owl was outfitted with the OwlCam and placed on a perch in a room. The room also contained 25 colored bars on the floor, with 24 of them oriented on the same direction. Across 97 experimental trials lasting 120 minutes, the owls' gazes were overwhelmingly drawn to the bar oriented differently from the rest. The owls looked at that bar more quickly, more often, and for longer periods of time than the other bars.

Orientation saliency is a common thread between barn owls and primates, despite large physiological and organizational differences between these animals' visual systems (interestingly, archerfish also exhibit orientation saliency). It remains to be seen whether a similar process drives this ability across groups, or whether these animals have found very different solutions. What is clear is that orientation saliency probably contributes greatly to barn owls' effectiveness in finding prey.

PNAS, 2011. DOI: 10.1073/pnas.1101582108 (About DOIs).