The Various Ways in Which Birds Blink.

Area of Science:

• Ornithology
• Comparative Zoology
• Animal Behavior

Background:

• No prior systematic study existed on the diverse mechanisms of avian blinking.
• Understanding blinking is crucial for avian eye health and function.

Purpose of the Study:

• To systematically document and categorize the different types of blinks observed in bird species.
• To compare avian blinking mechanisms with those of related species, such as crocodiles.

Main Methods:

• Digital video recordings of 524 bird species in zoos and the wild.
• Analysis of internet videos from an additional 106 bird species.
• Video recordings of 15 crocodile species for comparative analysis.

Main Results:

• Identified three distinct types of blinks in birds: nictitating membrane (phasic), upper eyelid, and lower eyelid (tonic).
• Observed nictitating membrane and lower eyelid blinks in crocodiles, but not upper eyelid blinks.
• Noted globe retraction in crocodiles, absent in birds; phasic blinks aid corneal oxygenation, tonic blinks offer protection.

Conclusions:

• Avian blinking exhibits diverse forms, including rapid phasic and slow tonic blinks, with upper eyelid blinking likely arising from convergent evolution.
• The observed differences in blinking mechanisms between birds and crocodiles suggest distinct evolutionary paths for ocular protection and function.
• Phasic blinks are vital for corneal health by removing debris and moistening, while tonic blinks serve a primarily protective role.