Whether it’s drumming a steady beat against a tree to attract a mate, weaving an intricate nest or just lifting food to their beaks, some birds engage in some truly fancy footwork.
Now researchers say the evolution of such dexterity may have been driven by the creatures taking up residence in trees.
“Our research shows that foot use is very rare outside of land birds,” said Cristián Gutiérrez-Ibáñez, an author of the research who is based at the University of Alberta. Land birds, also known as Telluraves, are defined by their ability to live in trees.
Writing in the journal Communications Biology, Gutiérrez-Ibáñez and colleagues report how they analysed 3,725 images and videos of birds using their feet, encompassing 1,054 bird species –about 10% of all bird species – and 64 different bird families. Out of the 64 families that use their feet, 60 are Telluraves.
The team recorded 10 foot behaviours, ranging from basic foot use – where a bird could use its claw to hold or grasp an object – to the ability to lift its foot to its beak.
While the former was fairly common across the species studied, with most birds able to hold down objects, the latter was rarer.
The team added that while parrots were able to manipulate objects with their feet the most, other species also showed skills. Among them, the palm cockatoo uses its feet to hold a stick to drum on trees to attract females, while the burrowing owl can use its feet to secure prey. Both birds are Telluraves.
The team also tested different evolutionary models made to explain the development of foot use. The results support the idea that the evolution of foot use and foot-based skills in birds would have been facilitated by a transition to strictly living in trees.
“Our best-supported models suggest that in order to evolve foot use, birds first had to evolve some other character, an unknown precursor,” Gutiérrez-Ibáñez said. “Our model shows that this precursor character evolved only once at the base of Telluraves.”
Gutiérrez-Ibáñez said living in trees resulted in a series of adaptations of the foot to be able to grasp branches. These included long toes, long claws and a stronger grip. Once they had these adaptations to grasp branches, birds could evolve the ability to hold objects with their feet.
“It has been suggested that living in trees for mammals is also important to evolve this ability to manipulate objects. Our study draws a parallel with that,” Gutiérrez-Ibáñez said. “It shows that in birds, a similar thing happened when moving into the trees. It’s an important step in the evolution of this skilful [foot] manipulation.”
Dr Joseph Tobias, a researcher at Imperial College London, who was not associated with the research, said other factors could also be at play.
“These findings also suggest that skilled use of the feet by birds is not just related to adaptations for perching on branches but also cognitive and behavioural changes that seem to have appeared in conjunction with the ability to grip and manipulate objects with the foot,” he said.