Cranial adaptations of the Night Parrot (Psittaculidae: Pezoporus occidentalis), a cryptic nocturnal bird

ABSTRACT The Night Parrot Pezoporus occidentalis is a critically endangered, elusive, nocturnal bird that is difficult to study in the field. Much is unknown about its biology, including how it navigates at night. A previous investigation of the eye and brain revealed that it likely has poor nocturnal vision, but its other sensory abilities, and overall skull anatomy, have not yet been investigated. This osteological study, based on micro-CT-scans of the holotype, describes and compares the anatomy of the Night Parrot skull, and identifies its possible ecological adaptations. Specialised ear anatomy suggests that the Night Parrot has enhanced acoustic abilities, in contrast with its diurnal congener P. wallicus and the only other nocturnal parrot, the Kakapo Strigops habroptila. The Night Parrot’s uniquely enlarged exoccipital bones may amplify sound, and bilateral ear asymmetry, not identified in any other parrot species, likely enhances its directional hearing, as in many species of owl. Enlarged exoccipitals displace the zygomatic processes and constrain orbit size, suggesting an evolutionary trade-off between hearing and vision. The auditory abilities of the species require deeper investigation, but our anatomical observations indicate that the potential impacts of noise disturbance may warrant consideration in Night Parrot conservation strategies as a precaution.