Abstract:Modern tree sloths are one of few mammalian taxa for which quadrupedal suspension is obligatory. Sloth limb musculature is specialized for slow velocity, large force contractions that stabilize their body below branches and conserves energy during locomotion. However, it is unknown if two and three-toed sloths converge in their use of limb biomechanics and whether these patterns are comparable to how primates perform arboreal suspensory locomotion. This study addresses this need by collecting limb loading data… Show more
“…All comparative data were drawn from literature values [ 64 , 65 ]. Figure 5 ( a ) Representative fore–aft plane force traces of a parrot ( Agapornis roseicollis ) compared with a representative brachiator (gibbon; Hylobates moloch [ 64 ]) and a representative inverted quadrupedal walker (sloth; Bradypus vareigatus [ 50 , 51 ]). The filled solid line represents the beak (parrot), forelimb (sloth) or left forelimb (gibbon); unfilled dashed line represents the hindlimb (parrot and sloth) or right forelimb (gibbon).…”
Section: Resultsmentioning
confidence: 99%
“…Here, we present the first biomechanical analysis of below-branch locomotion within parrots using a model species ( Agapornis roseicollis) , and contextualize the mechanics of this gait against other specialized suspensory tetrapods [ 48 , 50 , 51 , 63 , 67 ]. We demonstrate that parrots employ a distinct form of locomotion we coin beakiation, in which the beak initially secures a grip on the support followed by the simultaneous release of both hindlimbs.…”
Section: Discussionmentioning
confidence: 99%
“…130% BW) [ 64 , 66 ], and spider monkeys (125% BW) [ 64 ]. Similarly, in the fore–aft plane, parrots generate propulsive and braking forces that exceed 50% BW ( figure 5 ), greater than the equivalent forces seen in the forelimbs of both brachiating primates and non-specialized inverted quadrupeds ( figure 5 ; [ 48 , 50 , 51 , 63 , 64 , 67 ]). Thus, beakiation represents a true beak-driven mode of locomotion, in which the craniocervical system assumes a critical role in both supporting the body and generating propulsive movements.…”
Section: Discussionmentioning
confidence: 99%
“…Single limb forces were collected using a modified version of this apparatus following [48][49][50][51], in which the length of the support was reduced to 49.5 cm (comprising two uninstrumented 22.5 cm sections flanking a single instrumented 4.5 cm section). A smaller instrumented section was used for this second experiment to isolate the contact of a single hindlimb or beak without interference from other points of contact.…”
Section: Experimental Designmentioning
confidence: 99%
“…Filled bars represent beak or forelimb forces, unfilled bars represent hindlimb forces. All comparative data were drawn from literature values[35,[48][49][50][51][63][64][65][66].…”
Occupation of arboreal habitats poses myriad locomotor challenges, driving both anatomical and behavioural innovations across various tetrapod lineages. Here, we report and biomechanically assess a novel, beak-driven locomotor mode—‘beakiation’—by which parrots advance along the underside of narrow arboreal substrates. Using high-speed videography and kinetic analyses, we describe the limb loading patterns and pendular mechanics of beakiation, and compare the biomechanical characteristics of this gait with other suspensory behaviours (namely, forelimb-driven brachiation and inverted quadrupedal walking). We report that the parrot beak experiences comparable force magnitudes (approx. 150% body weight in the normal plane; approx. 50% body weight in the fore–aft plane) to the forelimbs of brachiating primates. Parrot beakiation is also characterized by longer-than-expected pendular periods, similar to observations of gibbon brachiation. However, in terms of mechanical energy recovery, beakiation is typified by lower levels of energetic recovery than brachiating specialists: a product of its slower, more careful nature. The observation of this novel behaviour—which adds to a growing base of literature regarding beak-assisted locomotor strategies in birds—highlights the extraordinary behavioural plasticity of birds, the functional versatility of the avian beak, and the difficulties in reconstructing an animal's locomotor repertoire from morphological characteristics alone.
“…All comparative data were drawn from literature values [ 64 , 65 ]. Figure 5 ( a ) Representative fore–aft plane force traces of a parrot ( Agapornis roseicollis ) compared with a representative brachiator (gibbon; Hylobates moloch [ 64 ]) and a representative inverted quadrupedal walker (sloth; Bradypus vareigatus [ 50 , 51 ]). The filled solid line represents the beak (parrot), forelimb (sloth) or left forelimb (gibbon); unfilled dashed line represents the hindlimb (parrot and sloth) or right forelimb (gibbon).…”
Section: Resultsmentioning
confidence: 99%
“…Here, we present the first biomechanical analysis of below-branch locomotion within parrots using a model species ( Agapornis roseicollis) , and contextualize the mechanics of this gait against other specialized suspensory tetrapods [ 48 , 50 , 51 , 63 , 67 ]. We demonstrate that parrots employ a distinct form of locomotion we coin beakiation, in which the beak initially secures a grip on the support followed by the simultaneous release of both hindlimbs.…”
Section: Discussionmentioning
confidence: 99%
“…130% BW) [ 64 , 66 ], and spider monkeys (125% BW) [ 64 ]. Similarly, in the fore–aft plane, parrots generate propulsive and braking forces that exceed 50% BW ( figure 5 ), greater than the equivalent forces seen in the forelimbs of both brachiating primates and non-specialized inverted quadrupeds ( figure 5 ; [ 48 , 50 , 51 , 63 , 64 , 67 ]). Thus, beakiation represents a true beak-driven mode of locomotion, in which the craniocervical system assumes a critical role in both supporting the body and generating propulsive movements.…”
Section: Discussionmentioning
confidence: 99%
“…Single limb forces were collected using a modified version of this apparatus following [48][49][50][51], in which the length of the support was reduced to 49.5 cm (comprising two uninstrumented 22.5 cm sections flanking a single instrumented 4.5 cm section). A smaller instrumented section was used for this second experiment to isolate the contact of a single hindlimb or beak without interference from other points of contact.…”
Section: Experimental Designmentioning
confidence: 99%
“…Filled bars represent beak or forelimb forces, unfilled bars represent hindlimb forces. All comparative data were drawn from literature values[35,[48][49][50][51][63][64][65][66].…”
Occupation of arboreal habitats poses myriad locomotor challenges, driving both anatomical and behavioural innovations across various tetrapod lineages. Here, we report and biomechanically assess a novel, beak-driven locomotor mode—‘beakiation’—by which parrots advance along the underside of narrow arboreal substrates. Using high-speed videography and kinetic analyses, we describe the limb loading patterns and pendular mechanics of beakiation, and compare the biomechanical characteristics of this gait with other suspensory behaviours (namely, forelimb-driven brachiation and inverted quadrupedal walking). We report that the parrot beak experiences comparable force magnitudes (approx. 150% body weight in the normal plane; approx. 50% body weight in the fore–aft plane) to the forelimbs of brachiating primates. Parrot beakiation is also characterized by longer-than-expected pendular periods, similar to observations of gibbon brachiation. However, in terms of mechanical energy recovery, beakiation is typified by lower levels of energetic recovery than brachiating specialists: a product of its slower, more careful nature. The observation of this novel behaviour—which adds to a growing base of literature regarding beak-assisted locomotor strategies in birds—highlights the extraordinary behavioural plasticity of birds, the functional versatility of the avian beak, and the difficulties in reconstructing an animal's locomotor repertoire from morphological characteristics alone.
Tree sloths evolved below‐branch locomotion making them one of few mammalian taxa beyond primates for which suspension is nearly obligatory. Suspension requires strong limb flexor muscles that provide both propulsion and braking/support, and available locomotor kinetics data indicate that these roles differ between fore‐ and hindlimb pairs. Muscle structure in the pelvic limb is hypothesized to be a key anatomical correlate of function in braking/support during suspensory walking and propulsion and/or support during vertical climbing. This expectation was tested by quantifying architecture properties in the hindlimb limb musculature of brown‐throated three‐toed sloths (Bradypus variegatus: N = 7) to distinguish the roles of the flexor/extensor functional muscle groups at each joint. Measurements of muscle moment arm (rm), mass, belly length, fascicle length, pennation angle, and physiological cross‐sectional area (PCSA) were taken from n = 45 muscles. Overall, most muscles studied show properties for contractile excursion and fast joint rotational velocity. However, the flexor musculature is more massive (p = 0.048) and has larger PCSA (p = 0.003) than the extensors, especially at the knee joint and digits where well‐developed and strong flexors are capable of applying large joint torque. Moreover, selected hip flexors/extensors and knee flexors have modified long rm that can amplify applied joint torque in muscles with otherwise long, parallel fascicles, and one muscle (m. iliopsoas) was capable of moderately high power in B. variegatus. The architectural properties observed in the hip flexors and extensors match well with roles in suspensory braking and vertical propulsion, respectively, whereas strong knee flexors and digital flexors appear to be the main muscles providing suspensory support in the pelvic limb. With aid in support by the forelimbs and the use of adaptive slow locomotion and slow muscle fiber recruitment patterns, structure–function in the tensile limb systems of sloths appears to collectively represent an additional mechanism for energy conservation.
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