The American Dipper is the only songbird in North America that can swim. Bob Armstrong had long wanted to capture the bird's underwater prowess on video, and in November 2014, in Juneau, Alaska, he got his wish.

He and a friend went to a stream frequented by the birds. "This is the result of many, many days of work," he says. "We sat and watched them, to see what they were doing and where they were going." When they found a spot where Dippers congregated, they tied a GoPro camera to a two-pound fishing weight and dropped it into the water. They left the area so as not to disturb the birds.

The Dipper's skill underwater is the result of its unique anatomy. The stocky grey bird's powerful wings allow it to swim against the current, while its strong toes help it to hunt aquatic insects and fish eggs hiding beneath stones and wood. A thick coat of waterproof feathers insulates the dipper from chilly waters, and the bird's blood carries extra oxygen, which helps it stay submerged during underwater forays.

Later that day, Armstrong downloaded the footage to his computer, and leaned back in his desk chair. About 45 minutes later, he saw it—a dipper plunging to the bottom of the stream. "It's extremely exciting" he says. "For most of the tape you don't see anything, and then 'Wham!' there it is."

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