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Owls have long been a source of fascination to people: The birds were imbued with wisdom and prophesy in early Indian folktales, considered a protector of ancient Greece, and even associated with witchcraft during the Middle Ages because of their “eerie” after-dark activities.

Part of this allure comes from their huge, round, forward-facing eyes, a feature that also makes them a popular subject for wildlife photographers. Yet the same nocturnal habits that linked owls with black magic also makes them difficult to photograph. To solve this problem, some photographers use flash—but whether it’s ethical to flash an animal that relies on keen, night-adapted vision to hunt has become a source of debate.

Unfortunately, there’s little scientific research on the topic, but we do know a little something about the way bird vision works.  The eyes of owls and humans respond to light in the same way, says Ellis Loew, a professor of physiology at Cornell University College of Veterinary Medicine. When the eye is exposed to bright light—like a flash firing in the dark—photoreceptor cells can become saturated. This causes brief “functional blindness,” a glowing afterimage that affects the ability to see and recognize objects. It can take anywhere from five to 30 seconds for vision to readjust.  

Loew doesn’t believe that a single flash, or maybe even a couple, would cause physical damage to an owl. But what if there were a group of photographers, say, in a photo workshop, all shooting at once or within a short time interval? Or a birding expedition coming regularly to the same location over weeks or months?

Depending on how many flashes, the frequency, and the total amount of light absorbed by the eyes’ photoreceptors, Loew says that continuous exposure might have physiological consequences. With one flash, there’s a short recovery time. But Loew thinks that repeated flashes at night might cause “flash blindness”: The photoreceptor cells might sustain temporary damage and would not “dark adapt” to the same level of sensitivity. This could lessen the bird’s visual acuity at night, and it could take longer to recover from being flashed. 

That would be particularly problematic if the bird is flashed when flying, as it might collide with an obstacle while temporarily blinded, or when adults are feeding their young and need to be searching for prey. “It takes a while to readjust after being flashed in the dark, and if during that time, a bird had to perform some critical life function, it would be at a disadvantage," Loew says. "During that period, it could not effectively hunt.”

Some experts, such as Denver Holt, director of the Montana-based Owl Research Institute, argue that the educational value of these images can outweigh the potential risk—if the images are used for greater public awareness and conservation, for example, and the photographer works in tandem with researchers who study and understand the particular species. He allows limited use of flash photography when his team bands owls at night.

While the damage flash can have on an owl's vision is not definitively known, other photography tricks have more demonstrable ill effects, such as baiting owls and flushing them from their roosts in the quest to create dramatic images. These methods combined with environmental issues like habitat loss only increase owls' overall stress levels. In fact, many species were included on the Watch List because they are at risk of extinction without concerted efforts to mitigate various threats.

“Fifteen years ago, you could probably do these things and it wouldn’t matter,” says Gerrit Vyn, a photographer and cinematographer with the Cornell Lab of Ornithology. “But now the pressure cannot be ignored, with so many people affecting these animals day after day.” People should be aware of the impacts and make decisions accordingly, he says, always placing the bird’s best interests first.

That's the realization photographer Mia McPherson came to some years back while using flash with barred owls in Florida. When she noticed that they often startled or woke, altering their behavior, she stopped the practice. “The subject is more important than the photo,” she says.