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Science. Communication. Community.

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Photo credit: Marcel Burkhard

Photo credit: Marcel Burkhard via Wikimedia Commons

Long before DC’s beloved snowy owl got hit by a bus, one resident said she saw calamity coming. Was she just a pessimist? Or do we know enough about owls (and buses) to do the math? 

By Rebecca Widiss

We thought we were lucky, here in DC, when a snowy owl took up residence in Dupont Circle. Even after learning that Boston has the “largest number of snowy owls ever recorded” we were happy with our lone star. Day after day, office workers flocked to see the owl in person. But then, our fledgling romance with nature took a nosedive. A bus hit the owl in mid-flight, a benevolent police chase ensued, and the owl wound up at the vet, recuperating from head trauma.

While romantics like me sat in shock, Ellen Paul, executive director of the Ornithological Council told the Washington Post it was bound to happen.

“I was pretty sure this bird was going to end up being hit by a vehicle because what happens when they focus on prey, they literally lock on it like a heat seeking missile,” she said. “And they’re going to go diving directly onto it and not even notice what else is around them.”

This got me to thinking. How do we really know what owls can see and what they focus on? Luckily, biologists have been chipping away at these two questions for years. Like Salinger offering his reader a bouquet of parentheses, I offer you the fruits of an evening spent Googling owl vision: two experiments and a wacky theory.

1. Getting to 3D

Documenting 3D vision takes a pretty nifty contraption. You fit polarized goggles—the glasses with one red filter and one green filter—on your owl-subject. Then you have it view random dot displays, which more are more than just ordinary images, they are stereograms. In these stereograms, each eye views an array of dots that is identical, except in the central region, where the dots seen by the left eye are slightly shifted, relative to those seen by the right eye. The effect of these shifts (for humans) is the perception of depth. The shifted dots might appear to form a rectangle hovering in front of the surrounding dots, or in back of them — or, as in the experiment illustrated below, a corrugated surface might appear. But what do owls see?

An owl at the movies. Image from a paper by Wolf Harmening and Hermann Wagner

An owl at the movies. Image credit: Harmening and Wagner, 2011, doi: 10.1007/s00359-011-0664-3

Here, as always, food comes in handy. In an experiment that involved hovering rectangles, biophysicist Robert van der Willigen taught two owls to peck response bars – one representing “in back”, the other “in front.” During training sessions, the right answer led to a treat. During testing sessions, owls were rewarded for every response, so as not to cause any frustration if the owls missed a question.

2. Attention

I wasn’t quite as lucky in my quest to find experiments on attention. They exist, of course, but most that I ran across focus out how owls find prey in the first place. Mount a tiny “owl cam” on your subject, for example, and put it in a roomful of bright objects, one of whom is edible. Even without being given a particular task, owls will look “significantly longer, more often, and earlier at the target.” According to the researchers involved, this visual search strategy has been previously shown only in primates.

Screen Shot 2014-02-12 at 7.25.53 AM

Image credit: Harmening, Orlowskia, Ben-Shaharb, and Wagner, 2011, doi: 10.1073/pnas.1101582108

Ironically, a trendy new hypothesis suggests that that owls’ spectacular vision may be an evolutionary afterthought. As owl ears became ever larger and more sensitive—a key asset for night hunting—very little space remained for large eyes. The result: owl eyes were effectively “packed into” their current, front-facing position. (Fun fact: these two organs are so closely located, you can see the back of an owl’s eye by peering into an owl’s ear.) This set the stage “for neurons that are binocularly driven” to evolve.

So maybe our poor snowy owl would have had a better chance, if the bus had just used its horn!

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This entry was posted on February 13, 2014 by in Nature, Uncategorized.
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