And the Fastest-Moving Birds on the Planet Are ...

Shocker: They aren't hummingbirds.

Most birds’ wings are built for strength, not speed. (Two tickets to the gun show, anyone?) But some birds, such as birds-of-paradise, Ruffed Grouse, and of course, hummingbirds, make extremely rapid movements with their wings as part of their courtship displays.

Exactly how their muscles produce such quick motions has remained a mystery until now: According to a study published this month in the journal eLife, at least two tropical songbird species found in Latin America—Golden-collared Manakins and Red-capped Manakins—appear to have evolved the ability to balance lightning-fast reflexes with super strength in their humeral (inner-wing) muscles. But the most surprising finding is not that they can produce these movements, but just how rapidly their wings can move, says lead author Matthew Fuxjager, an assistant professor at Wake Forest University. “To my knowledge, we uncovered the fastest vertebrate limb muscle on record.”

Fuxjager and his colleagues used electrodes to stimulate three different wing muscles in five wild species of closely related passerine birds. All of the subjects have been known to incorporate speedy wing movements into their courtship behaviors: the Golden-collared Manakin, the Red-capped Manakin, the Blue-crowned Manakin, the Dusky Antbird, and the House Wren. The team connected a sensor on or near the birds’ muscles to determine how quickly they contracted and relaxed. This allowed the researchers to determine how quick each succession of wing movements was.

The Golden-collared Manakin's "roll-snap" in slow motion. Video: Barney Schlinger

It turns out that the Golden-collared and Red-capped manakins produce the fastest twitch in their humeral muscles. Though these muscles are crucial for flight, male manakins seem to tap their agility primarily for attracting mates. During their courtship displays—which also involve a lot of hopping and dancing (see the clip below)—Golden-collared Manakins use the muscles to "roll-snap" their wings, hitting them together above their backs to create a repetitive snapping sound. Similarly, Red-capped Manakins hop, dance, and clap their wings against the sides of their bodies.

The speedy movements in manakin muscles may be mimicked in human muscles, Fuxjager says. “Given that we're working to uncover how birds' muscles achieve super-fast contractile speeds, our findings might provide insight into possible therapies for muscle-wasting disorders,” he says. This goal may be much further down the road, so until then we can sit back and be amazed by the manakins' superpowers.

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