Macaws are renowned for processing dry, mechanically resistant fruits, yet the species-level anatomical and functional correlates of this performance remain incompletely resolved. We examined the feeding apparatus of the Blue-and-yellow Macaw (Ara ararauna) using an integrated approach that combines osteology, myology, and bite-force estimates derived from physiological cross-sectional area (PCSA). The skull is highly pseudokinetic, allowing a wide gape and comparatively strong beak-opening capacity (65 N), which likely facilitates handling of large food items. PCSA-based modeling yielded an estimated total bite force of 232.74 N, with ~98% contributed by the m. adductor mandibulae externus (82.52 N), m. pterygoideus (101.06 N), and m. ethmomandibularis (43.43 N). These principal adductor muscles show largely near-perpendicular lines of action, a configuration consistent with increased PCSA and elevated force output. Generated forces are transmitted to a robust mandible, enhancing compressive efficiency at the rostral bite point, and act in concert with an enlarged, curved, tapered maxilla to form a pincer-like functional unit. A thick rhamphotheca bearing aligned ridges and tubercles likely increases contact stability and promotes fracture of resistant foods. The maxillary tip also functions as a lever and, together with cervical musculature, may assist shell cracking via dorsal head movements. Skeletal reinforcement-including a well-developed arcus jugalis and palatinum, a robust arcus suborbitalis articulating with the lacrimalis, and a deeply congruent quadrato-mandibular joint-improves joint stability and resistance to feeding-induced stresses. Collectively, these features provide a structural basis for transmitting high bite forces in the Blue-and-yellow Macaw during hard-fruit exploitation.
Posso et al. (2026) studied this question.