Capturing Wildlife With An Infrared Trigger

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In the neotropics, nocturnal bats fill many of the niches occupied by birds by day. But where birds use their superb sense of sight, bats exploit their specialized sense of hearing to find prey. They produce high-frequency clicking sounds and listen with finely tuned ears for the echoes—then strike. Besides insects, bulldog bats have another food source: They hunt for fish over open water just after dusk, echolocating through their open mouths to pinpoint the position of fish near the water surface.

At a research station along the Panama Canal, I teamed up with a biologist to photograph bulldog bat behavior. After observing bats for several nights in a backwater lagoon, I made a move. I rigged up a camera system with strobes triggered by an infrared sensor. All the components were clamped onto PVC tubes pushed into the mud along a shoreline where we had seen bats coming and going. I wanted to capture an eye-level view of a bat swooping over the water, which required the camera and the sensor to be mounted just inches above the water surface. The position and the output of each of the six strobes—two for the front, two for the sides and two for backlighting—had to be determined separately and then integrated for the final deployment. Working with camera traps to document animal behavior is always a feat involving solutions to both high-tech systems requirements and improvised responses to natural challenges, but in this situation, the Panama Canal raised the stakes even higher. Large ships passing by in the distance caused surges in the water level, and several times, my system was nearly swamped.

But after several nights of trial and error, I was able to fine-tune the setup to produce some revealing images. And in this frame you can actually see a bat at the instant it broke the infrared beam, aiming its clicks toward me—just as my camera clicked back.

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