Online repositories of photographs and videos provide insights into the evolution of skilled hindlimb movements in birds

Abstract

The ability to manipulate objects with limbs has evolved repeatedly among land tetrapods. Several selective forces have been proposed to explain the emergence of forelimb manipulation, however, work has been largely restricted to mammals, which prevents the testing of evolutionary hypotheses in a comprehensive evolutionary framework. In birds, forelimbs have gained the exclusive function of flight, with grasping transferred predominantly to the beak. In some birds, the feet are also used in manipulative tasks and appear to share some features with manual grasping and prehension in mammals, but this has not been systematically investigated. Here we use large online repositories of photographs and videos to quantify foot manipulative skills across a large sample of bird species (>1000 species). Our results show that a complex interaction between niche, diet and phylogeny drive the evolution of manipulative skills with the feet in birds. Furthermore, we provide strong support for the proposition that an arboreal niche is a key element in the evolution of manipulation in land vertebrates. Our systematic comparison of foot use in birds provides a solid base for understanding morphological and neural adaptations for foot use in birds, and for studying the convergent evolution of manipulative skills in birds and mammals.

Discrete somatotopic representation and neural response properties in hummingbird and zebra finch forebrain nuclei

“…This phenomenon of “cortical magnification” – the preferential allocation of the cortical real estate to behaviorally significant sensory receptors such as the surfaces of the hands and lips in primates reflected in primary somatosensory cortex 33 – is thought to contribute to increased sensory resolution for important areas of the body periphery. As this appears to be the case in the barn owl (to the extent that the body is no longer represented within the somatosensory Wulst), further physiological research employing falcons, hawks, and parrots 34 , all birds that have been shown to use their feet for particularly complex manipulations, could shed light on more specific granular representation of the foot surface within the Wulst. Physiological and anatomical examinations of the nucleus basorostralis in the dunlin (an avian probe-feeding specialist) 35 suggest that preferential expansion in representation of important sensory surfaces (e.g., the bill tip) might potentially be found among other birds.…”

“…This inverse relationship between receptive field surface area and absolute mechanical thresholds of sensitivity has been explored in other vertebrates, including in close avian relatives, the archosaurs 38 . Given the prominent representation of the claw in both the owl basorostralis 31 and the foot in the rostral Wulst in hummingbirds and finches, combined with recent insight into the diversity of foot usage among diverse bird lineages 34 , further investigation of tactile specialization of the avian hindlimb and its representation within the telencephalon could yield insight into general principles of sensory adaptation.…”

Patterns of integrated growth of body parts in Rook (Corvus frugilegus) ontogeny

“…Synchronization of the development of these regions is probably also a direct preparation for independent feeding and adult type of terrestrial locomotion after leaving the nest. On the other hand, synchronization of head and pelvic limb increments may also have a broader significance in that these regions are involved in a search for food in adults and the pelvic limbs have considerable multifunctionality (Gutiérrez-Ibáñez et al, 2023). Previously, coevolution of the skull and the hind limb variables was noted among definitive individuals of Fringillinae and Carduelinae (Van Den Elzen & Nemeschkal, 2008).…”

Topography of visual and somatosensory inputs to the pontine nuclei in zebra finches (Taeniopygia guttata)

“…present in chickens (Gallus gallus) (Adamo, 1967) or pigeons . Recently, Gutiérrez-Ibáñez et al (2023) showed that skilled foot-use has evolved repeatedly among birds, but almost exclusively after the emergence of Telluraves (core landbirds) about 65 million years ago (Gutiérrez-Ibáñez et al, 2023). Zebra finches, ravens, owls and parrots are all Telluraves, whereas chickens and pigeons are not.…”