Fred Ruhe
Well-known member
John G. L. Morris and Jesse J. Parsons, 2023
The Various Ways in Which Birds Blink
Animals 13(23): 3656
doi: https://doi.org/10.3390/ani13233656
https://www.mdpi.com/2076-2615/13/23/3656
Simple Summary
While our blink simply involves lowering the upper eyelid, with little involvement of the lower lid, birds have various ways of blinking depending on the species and the circumstances. Like us, they have upper and lower eyelids, though the upper lid only moves down in parrots, owls, pigeons, and a few others. The lower lid rises with drowsiness and when the bird is preening. Birds blink when they turn their heads using a ‘third eyelid’, the nictitating membrane which moves horizontally from the inner part to the outer part of the eye. The closest cousins of birds, crocodiles, blink with their lower lids and nictitating membranes but not their upper lids. As crocodiles have changed very little since they first appeared, it seems likely that their way of blinking is similar to that of the common ancestor of birds and crocodiles, the archosaur. So, upper lid blinking in birds probably came later than lower eyelid and nictitating membrane blinking. The orders of bird which have upper lid blinking are not closely related, so this type of blink is likely to be an example of convergent evolution where distantly related species evolve similar traits to adapt to similar needs. Blinking evolved as a way of keeping the cornea moist when fish first left the sea and is an as yet neglected marker of vertebrate evolution.
Enjoy,
Fred
The Various Ways in Which Birds Blink
Animals 13(23): 3656
doi: https://doi.org/10.3390/ani13233656
https://www.mdpi.com/2076-2615/13/23/3656
Simple Summary
While our blink simply involves lowering the upper eyelid, with little involvement of the lower lid, birds have various ways of blinking depending on the species and the circumstances. Like us, they have upper and lower eyelids, though the upper lid only moves down in parrots, owls, pigeons, and a few others. The lower lid rises with drowsiness and when the bird is preening. Birds blink when they turn their heads using a ‘third eyelid’, the nictitating membrane which moves horizontally from the inner part to the outer part of the eye. The closest cousins of birds, crocodiles, blink with their lower lids and nictitating membranes but not their upper lids. As crocodiles have changed very little since they first appeared, it seems likely that their way of blinking is similar to that of the common ancestor of birds and crocodiles, the archosaur. So, upper lid blinking in birds probably came later than lower eyelid and nictitating membrane blinking. The orders of bird which have upper lid blinking are not closely related, so this type of blink is likely to be an example of convergent evolution where distantly related species evolve similar traits to adapt to similar needs. Blinking evolved as a way of keeping the cornea moist when fish first left the sea and is an as yet neglected marker of vertebrate evolution.
Enjoy,
Fred
