Inertial Tail Effects during Righting of Squirrels in unexpected Falls: From Behavior to Robotics

Arboreal mammals navigate a highly three dimensional and discontinuous habitat. Among arboreal mammals, squirrels demonstrate impressive agility. In a recent ‘viral’ YouTube video, unsuspecting squirrels were mechanically catapulted off of a track, inducing an initially uncontrolled rotation of the body. Interestingly, they skillfully stabilized themselves using tail motion, which ultimately allowed the squirrels to land successfully. Here we analyze the mechanism by which the squirrels recover from large body angular rates. We analyzed from the video that squirrels first use their tail to help stabilizing their head to visually fix a landing site. Then the tail starts to rotate to help stabilizing the body, preparing themselves for landing. To analyze further the mechanism of this tail use during mid-air, we built a multibody squirrel model and showed the righting strategy based on body inertia moment changes and active angular momentum transfer between axes. To validate the hypothesized strategy, we made a squirrel-like robot and demonstrated a fall-stabilizing experiment. Our results demonstrate squirrel’s long tail, despite comprising just 3% of body mass, can inertially stabilize a rapidly rotating body. This research contributes to better understanding the importance of long tails for righting mechanisms in animals living in complex environments such as trees.

Do substrate roughness and gap distance impact gap-bridging strategies in arboreal chameleons?

Chameleons are well equipped for an arboreal lifestyle, having “zygodactylous” hands and feet as well as a fully prehensile tail. However, to what degree tail use is preferred over autopod prehension has been largely neglected. Using an indoor experimental set-up, where chameleons had to cross gaps of varying distances, we tested the effect of substrate diameter and roughness on tail use in Chamaeleo calyptratus. Our results show that when crossing greater distances, C. calyptratus is more likely to use its tail for additional stability. The animals were able to cross greater distances (up to 1.75 times the shoulder-hip length) on perches with a rougher surface. We saw that depending on the distance of the gap, chameleons would change how they use their prehensile tails when crossing. With shorter gaps the tails either do not touch, or only touch the perch without coiling around it. With larger distances the tails are fully coiled around the perch, and with the largest distances additionally they reposition the hind legs, shifting them towards the end of the perch. Males were able to cross relatively greater distances than females, likely due to their larger size and strength.

Do substrate roughness and gap distance impact gap-bridging strategies in arboreal chameleons

Chameleons are well-equipped for an arboreal lifestyle, having ‘zygodactylous’ hands and feet as well as a fully prehensile tail. However, to what degree tail use is preferred over autopod prehension has been largely neglected. Using an indoor experimental set-up, where chameleons had to cross gaps of varying distances, we tested the effect of substrate diameter and roughness on tail use in Chamaeleo calyptratus. Our results show that when crossing greater distances, C. calyptratus is more likely to use its tail for additional stability. The animals were able to cross greater distances (up to 1 75 times the shoulder-hip length) on perches with a rougher surface. We saw that depending on the distance of the gap, chameleons would change how they use their prehensile tails when crossing. With shorter gaps the tails either do not touch, or only touch the perch without coiling around it. With larger distances the tails are fully coiled around the perch, and with the largest distances additionally they reposition the hind legs, shifting them towards the end of the perch. Males were able to cross relatively greater distances than females, likely due to their larger size and strength.

Observations on the diet and behaviour of captive Monodelphis (Mygalodelphys) kunsi Pine, 1975 (Didelphimorphia: Didelphidae) from Paraguay

We report data on the feeding preferences and behaviour of the little known didelphid Monodelphis (Mygalodelphys) kunsi, based on captive observations of a sub-adult female and a presumed sub-adult male. The behaviour observed is very similar to that documented for the better-known member of the genus, Monodelphis domestica. We confirm previously suspected prehensile tail use and tentatively suggest the species is insectivorous/carnivorous.

Walking on five legs: investigating tail use during slow gait in kangaroos and wallabies

Pentapedal locomotion is the use of the tail as a fifth leg during the slow gait of kangaroos. Although previous studies have informally noted that some smaller species of macropodines do not engage in pentapedal locomotion, a systematic comparative analysis of tail use during slow gait across a wide range of species in this group has not been done. Analysis of relative movement of the pelvis, tail, and joint angles of the lower limbs during slow gait, using 2D landmark techniques on video recordings, was carried out on 16 species of Macropodinae. We also compared the relative lengthening of the tibia using crural index (CI) to test whether hindlimb morphology was associated with pentapedal locomotion. Pentapedal locomotion was characterised by three features: the presence of the ‘tail repositioning phase’, the constant height of the pelvis and the stationary placement of the distal tail on the ground during the hindlimb swing phase. The mean CI of pentapedal species was significantly greater than that of non-pentapedal species (1.71 versus 1.36; P < 0.001). This lends support to the hypothesis that the use of pentapedal locomotion is associated with the relative lengthening of the hindlimb, which in turn is associated with body size and habitat preference within the Macropodinae.