Abstract
The Night Parrot (Pezoporus occidentalis) is a rare, nocturnal parrot species that has largely escaped scientific investigation due to its behaviour and habitat preferences. Recent field studies have revealed some insights into Night Parrot behaviour, but nothing is known of its sensory abilities. Here, we used μCT scans of an intact Night Parrot specimen to determine if its visual system shares similarities with other nocturnal species. The endocast of the Night Parrot revealed relatively small optic lobes and optic foramina, especially compared with closely related grass parakeets, but no apparent differences in orbit dimensions. Our data suggests that the Night Parrot likely has lower visual acuity than most other parrots, including its congener, the Eastern Ground Parrot (P. wallicus). We propose that the visual system of the Night Parrot might represent a compromise between the need to see under low light conditions and the visual acuity required to detect predators, forage, and fly. Based on the endocast and optic foramen measurements, the Night Parrot fits into a common pattern of decreased retinal input to the optic lobes in birds that should be explored more thoroughly in extant and extinct species.
Highlights
The Night Parrot (Pezoporus occidentalis) is considered to be one of the world’s most elusive birds[1]
The endocast had a volume of 2,478.07 mm[2], which relative to body mass is typical of other small parrots (Fig. 1c) and similar to that of the Eastern Ground Parrot (Pezoporus wallicus)
The optic lobes of the Night Parrot falls outside of the 95% interval of our phylogenetically informed posterior probability distributions. It exceeds the 99% interval, indicating that the surface area of the Night Parrot’s optic lobes is far below that predicted by its total endocast surface area
Summary
The Night Parrot (Pezoporus occidentalis) is considered to be one of the world’s most elusive birds[1] It is a small (100 g), highly cryptic, nocturnal parrot that lives only in the arid interior of Australia. The shrinkage of the Kakapo optic tectum coincides with a decrease in size of the optic foramen, which houses the optic nerve, as well as fewer retinal ganglion cells[16]. These anatomical changes result in the Kakapo possessing a visual system with a greater ability to capture photons under low light (higher sensitivity), but a relatively poor ability to discriminate among visual stimuli (lower acuity) compared to diurnal parrots[17]. We expected a reduction of lesser magnitude than what was found in the Kakapo because Night Parrots fly considerable distances between roosting and feeding areas[6], probably making them more dependent on vision[27]
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