Anatomical specializations for nocturnality in a critically endangered parrot, the Kakapo (Strigops habroptilus)
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Date
2011
Authors
Corfield, Jeremy R.
Gsell, Anna C.
Brunton, Dianne
Heesy, Christopher P.
Hall, Margaret I.
Acosta, Monica L.
Iwaniuk, Andrew N.
Journal Title
Journal ISSN
Volume Title
Publisher
Public Library of Science
Abstract
The shift from a diurnal to nocturnal lifestyle in vertebrates is generally associated with either enhanced visual sensitivity or
a decreased reliance on vision. Within birds, most studies have focused on differences in the visual system across all birds
with respect to nocturnality-diurnality. The critically endangered Kakapo (Strigops habroptilus), a parrot endemic to New
Zealand, is an example of a species that has evolved a nocturnal lifestyle in an otherwise diurnal lineage, but nothing is
known about its’ visual system. Here, we provide a detailed morphological analysis of the orbits, brain, eye, and retina of the
Kakapo and comparisons with other birds. Morphometric analyses revealed that the Kakapo’s orbits are significantly more
convergent than other parrots, suggesting an increased binocular overlap in the visual field. The Kakapo exhibits an eye
shape that is consistent with other nocturnal birds, including owls and nightjars, but is also within the range of the diurnal
parrots. With respect to the brain, the Kakapo has a significantly smaller optic nerve and tectofugal visual pathway.
Specifically, the optic tectum, nucleus rotundus and entopallium were significantly reduced in relative size compared to
other parrots. There was no apparent reduction to the thalamofugal visual pathway. Finally, the retinal morphology of the
Kakapo is similar to that of both diurnal and nocturnal birds, suggesting a retina that is specialised for a crepuscular niche.
Overall, this suggests that the Kakapo has enhanced light sensitivity, poor visual acuity and a larger binocular field than
other parrots. We conclude that the Kakapo possesses a visual system unlike that of either strictly nocturnal or diurnal birds
and therefore does not adhere to the traditional view of the evolution of nocturnality in birds.
Description
Sherpa Romeo green journal: open access
Keywords
Kakapo , Strigops habroptilus , Nocturnal , Diurnal , Visual system , Visual pathway , Morphological analysis
Citation
Corfield, J. R., Gsell, A. C., Brunton, D., Heesy, C. P., Hall, M. I., Acosta, M. L., & Iwaniuk, A. N. (2011). Anatomical specializations for nocturnality in a critically endangered parrot, the Kakapo (Strigops habroptilus). PLoS ONE, 6(8), e22945. doi:10.1371/journal.pone.0022945