Why Birds Can Sleep on Branches and Not Fall Off - Alexis C. Madrigal - The Atlantic: "You ever see a bird clutching onto a branch high in a tree and wonder, "What happens if it falls asleep? How could it hold on?"
The avian talon works through a "pulley system of tendons," according to the animal morphology blog Ars Anatomica, and it can lock into place.
"The bird's foot closes and grasps automatically as the ankle and knee joints are bent," we read. "This grasp cannot be released until the limb is straightened again." "
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