Research from the New York Institute of Technology College of Osteopathic Medicine reveals that parrots use their heads as a third propulsive limb. No vertebrate, including fish, mammals, birds, reptiles, or amphibians, has ever displayed an odd total number of limbs. Yet, some animals seem to borrow other body parts as a third or fifth limb to move from one place to another.
For instance, although parrots cannot grasp with their wings, they climb by extending their heads and gripping branches or surfaces with their beaks. It remains unclear whether the head acts as a true third limb that drives movement or whether the beak primarily provides self balancing by anchoring the body for support. Although parrots are widely admired for their remarkable intelligence, there is a notable gap in studies focused on their locomotor behavior.
A study published in the Proceedings of the Royal Society analyzed the climbing steps of pink-faced parakeets, a small parrot species known as Agapornis roseicollis. Researchers designed a series of experiments where parrots climbed a man-made vertical path set at angles from zero to 90 degrees. Two high-speed cameras captured the movement while a small force plate mounted on the back of the track measured the forces generated by the beak, hind legs, and tail as each body part contacted the surface.
Agapornis, the species used in the experiment
The parrots first touched the runway with their beaks at a 45-degree angle, and at a 90-degree incline, the beak produced forces comparable to those generated by the hind legs. In fact, beak forces matched or exceeded the forces known to be produced by human limbs or other large primates during climbing. By contrast, the tail generated minimal force, indicating it served mainly for balance and support rather than acting as an additional limb.
Representative findings highlight that parrot anatomy has evolved over many years to support these inventive climbing behaviors. The researchers observed that neck flexors and neural circuitry in the spine appear to have adapted to provide increased strength, enabling the beak to function as a potent propulsive element during ascent.
The only animal that does this
Although many birds climb vertically, parrots stand out as the only known avian group to employ the head as a third limb. This behavior seems to reflect neuromuscular changes over time, with anatomical adaptations that enhance neck control and coordination. These developments appear to confer a notable climbing advantage for parrots and may set them apart from other species in the animal kingdom, according to the researchers.
Experts in the evolution of animal movement suggest that parrots innovative climbing behavior could mark a distinctive feature in this lineage. The findings point to a remarkable convergence of anatomy and neuromuscular function that enables unique locomotion strategies not observed in other birds.
While young pandas are observed moving their heads laterally when ascending vertical surfaces, their movements do not involve contact with the surface in the same way. The use of the head as a propulsive limb represents an evolutionary step forward, a capability that, as far as current knowledge goes, appears exclusive to parrots.
This project represents the initial phase of a broader research program focused on avian locomotion. Parrots constitute an ancient tree-dwelling lineage that shares several anatomical and behavioral parallels with living primates, making them a compelling subject for comparative studies of movement and biomechanics.
In the coming years, researchers will continue to investigate the anatomical and neuromuscular underpinnings of this unusual climbing behavior and explore potential bio-inspired robotic applications. The aim is to simulate this movement in machines and to better understand how such locomotion could inform the design of advanced grasping and climbing systems.
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