Two Thumbs Up – Meet the Alula

Hovering as she hunted for flying insects at a Montana pond, this female Red-winged Blackbird was able to keep from “stalling out” by redirecting air flow over her wings with her alulae, the tufts sticking up on the fore edge of her wings.

It’s easy to find oneself marveling at the ease and grace with which a raptor or songbird flies – the seamless changes of direction, the steep climbs, the ability to hover, the smooth landings. Aiding in these intricate maneuvers is a small tuft of tiny feathers that the bird can manipulate to create a pocket of whirling air – a vortex – which helps it finesse some of its most amazing moves.

It appears that the alula evolved approximately 130 million years ago during the Cretaceous Period, first in genus Protopteryx and a few million years later in Eoalulavis, or Dawn Bird. Earlier species such as the bird-like dinosaur Archaeopteryx, Old Wing, lacked alulae, indicating that while they probably were capable of gliding, they most likely did not fly in the sense that modern birds fly.

 

Bearing 3 to 5 small, asymmetrical flight feathers, the alula is found on modern bird species as well as on some pre-avian dinosaurs that were capable of flight. It’s the bird’s first digit, analogous to the human thumb. Illustrations courtesy of: Muriel Gottrop – https://commons.wikimedia.org/wiki/File:BirdWingFeatherSketch.png