What does climbing mean exactly? Assessing spatiotemporal gait characteristics of inclined locomotion in parrots

At what inclination does climbing begin? In this paper, we investigate the transition from walking to climbing in two species of parrot (Agapornis roseicollis and Nymphicus hollandicus) that are known to incorporate both their tail and their craniocervical system into the gait cycle during vertical climbing. Locomotor behaviors ranging in inclination were observed at angles between 0° and 90° for A. roseicollis, and 45°-85° degrees for N. hollandicus. Use of the tail in both species was observed at 45° inclination, and was joined at higher inclinations (> 65°) by use of the craniocervical system. Additionally, as inclination approached (but remained below) 90°, locomotor speeds were reduced while gaits were characterized by higher duty factors and lower stride frequency. These gait changes are consistent with those thought to increase stability. At 90°, A. roseicollis significantly increased its stride length, resulting in higher overall locomotor speed. Collectively these data demonstrate that the transition between horizontal walking and vertical climbing is gradual, incrementally altering several components of gait as inclinations increase. Such data underscore the need for further investigation into how exactly "climbing" is defined and the specific locomotor characteristics that differentiate this behavior from level walking.

Positional Behavior of Introduced Monk Parakeets (Myiopsitta monachus) in an Urban Landscape

Simple Summary

Positional behaviors comprise the entirety of animals’ locomotion and posture. Often, these positional behaviors are paired with information about sußbstrate characteristics (e.g., orientation, diameter, texture, height) and frequency to gain an ecological perspective of when and why an animal utilizes a particular behavior. Thus far, quantitative studies of positional behavior have been limited to mammals, leaving a major gap in our understanding of how animals utilize their environment. In this study, we present the first quantitative report of positional behavior within Aves, presenting scan sampling data from an established colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Parrots exhibited a strong preference for small and terminal branches when perching arboreally. Such a pattern is consistent with arboreal primates. We also observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the potential importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species and underscores the need for further studies exploring positional behaviors among urban wildlife.

Abstract

Positional behaviors have been broadly quantified across the Order Primates, and in several other mammalian lineages, to contextualize adaptations to, and evolution within, an arboreal environment. Outside of Mammalia, however, such data are yet to be reported. In this study, we present the first quantitative report of positional behavior within Aves, presenting 11,246 observations of scan sampling data from a colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Each scan recorded locomotor and postural behavior and information about weather condition, temperature, and substrate properties (e.g., type, size, orientation). A distinction was also recorded between natural and artificial substrates. Parrots exhibited a strong preference for small and terminal branches, a selection which may reflect targeted foraging of new fruit growth and leaf-buds. We further observed that the gait transition from walking to sidling appears primarily driven by substrate size, with the former preferred on the ground and on large, broad substrates and the latter used to navigate smaller branches. Finally, we observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species.

Mudskippers modulate their locomotor kinematics when moving on deformable and inclined substrates

Many ecological factors influence animal movement, including properties of the media that they move on or through. Animals moving in terrestrial environments encounter conditions that can be challenging for generating propulsion and maintaining stability, such as inclines and deformable substrates that can cause slipping and sinking. In response, tetrapods tend to adopt a more crouched posture and lower their center of mass on inclines and increase the surface area of contact on deformable substrates, such as sand. Many amphibious fishes encounter the same challenges when moving on land, but how these finned animals modulate their locomotion with respect to different environmental conditions and how these modifications compare with those seen within tetrapods is relatively understudied. Mudskippers (Gobiidae: Oxudercinae) are a particularly noteworthy group of amphibious fishes in this context given that they navigate a wide range of environmental conditions, from flat mud to inclined mangrove trees. They use a unique form of terrestrial locomotion called 'crutching', where their pectoral fins synchronously lift and vault the front half of the body forward before landing on their pelvic fins while the lower half of the body and tail are kept straight. However, recent work has shown that mudskippers modify some aspects of their locomotion when crutching on deformable surfaces, particularly those at an incline. For example, on inclined dry sand, mudskippers bent their bodies laterally and curled and extended their tails to potentially act as a secondary propulsor and/or anti-slip device. In order to gain a more comprehensive understanding of the functional diversity and context-dependency of mudskipper crutching, we compared their kinematics on different combinations of substrate types (solid, mud, dry sand) and inclines (0°, 10°, 20°). In addition to increasing lateral bending on deformable and inclined substrates, we found that mudskippers increased the relative contact time and contact area of their paired fins while becoming more crouched, responses comparable to those seen in tetrapods and other amphibious fishes. Mudskippers on these substrates also exhibited previously undocumented behaviors, such as extending and adpressing the distal portions of their pectoral fins more anteriorly, dorsoventrally bending their trunk, "belly-flopping" on sand, and "gripping" the mud substrate with their pectoral fin rays. Our study highlights potential compensatory mechanisms shared among vertebrates in terrestrial environments while also illustrating that locomotor flexibility and even novelty can emerge when animals are challenged with environmental variation.