Blinking is something we humans do constantly without even thinking about it. But have you ever wondered if other animals like alligators blink? Many people are curious if those unblinking alligator eyes are really as motionless as they seem.
If you want a quick answer: Yes, alligators do blink, but not as frequently or completely as humans.
In this comprehensive article, we’ll take a close look at alligator eyes to understand how blinking works in these reptiles. We’ll compare alligator blinking to human blinking, and explain why these ancient creatures don’t need to blink as often as we do.
Anatomy of Alligator Eyes
Eyelids
Alligators have movable upper and lower eyelids that protect their eyes and help keep them moist. The upper eyelid has a transparent nictitating membrane that can slide horizontally across the eye to protect it.
When underwater, the nictitating membrane acts like goggles, allowing the alligator to see while also keeping debris out of the eye.
Interestingly, alligators cannot completely close their eyes since their lower eyelids lack muscles. Their eyes remain slightly open even when asleep. This allows them to still monitor their surroundings for possible danger.
However, alligators have a protective bony ridge over their eyes that shields them when closed.
Nictitating Membrane
The nictitating membrane is a transparent or translucent third eyelid found in reptiles, birds, and some mammals. In alligators, it is located under the upper eyelid and slides horizontally across the eye from the inner corner to the outer corner.
This membrane helps protect and moisten the alligator’s eyes while allowing it to see underwater. When swimming, the alligator can close its outer eyelids while the nictitating membrane acts like built-in goggles, giving underwater vision. It also clears away debris and spreads tears across the eye.
Tear Ducts
Alligators have tear ducts that produce tears to lubricate and clean their eyes. Tears contain salts, mucus, antibodies, and oils that help prevent eye infections and remove irritants like dust or dirt.
On land, gravity pulls the alligator’s tears down the tear ducts and out openings at the corners of the eyes. Underwater, the nictitating membrane spreads the tears across the eye’s surface. Alligators produce more tears when out of water to keep their eyes from drying out.
How Often Do Alligators Blink?
Blink Rate Compared to Humans
Alligators blink at a much slower rate compared to humans. On average, humans blink around 15-20 times per minute. However, alligators only blink 4-5 times per minute. Their blink rate is around 4 times slower than the average person.
There are a few key reasons for this slower blink rate in alligators:
- As ambush predators that spend a lot of time floating in water perfectly still, alligators need to keep their eyes open for long periods to spot potential prey.
- With protective transparent third eyelids called nictitating membranes, alligators can keep their eyes moist while remaining open for extended times.
- Their eyes have adapted over evolution to require less frequent blinking.
Factors That Influence Blinking
While alligators generally have a lethargic blink rate, some factors can influence how often they blink:
| Factor | Effect on Blink Rate |
|---|---|
| Air exposure | More frequent blinking when on land due to eyes drying out faster |
| Hunting activity | Reduced blinking when eyeing and stalking prey in water |
| Illness or injury | Increased blinking which may indicate infection or irritation |
| Shedding skin | Extra eyelid protective membrane sheds with old skin, causing more blinking |
So while alligators naturally have an exceptionally slow blink rate, certain environmental and biological factors can lead to some fluctuation.
To learn more, visit this informative site on alligator facts.
Functions of Blinking in Alligators
Keeping the Eyes Moist
Like humans, alligators blink to distribute tears across and remove debris from the surface of their eyes to keep them moist (1). An alligator’s eyes are protected by three eyelids, including a very thin bottom lid called the nictitating membrane.
This thin membrane allows an alligator to see while underwater even when its eyes are closed. When an alligator blinks, the nictitating membrane sweeps across the eye to keep it clean and moist while the upper and lower lids wipe debris away (2).
Without blinking and the coating of tears across the eye, the surface would dry out.
Protecting the Eyes
Blinking also serves to temporarily protect an alligator’s eyes from injury. When attacking prey, alligators close their eyes just before their mouths clamp down to shield them from claws and sharp bones (3).
Blinking can also guard the eyes against foreign objects or irritants like dirt, dust, or even rain falling into them. Slow blinking movements prevent excess tear production that can blur their vision (4).
Interestingly, alligators can voluntarily submerge their eyes under their eyelids while exposing the rest of the eyeballs. This protects their vision when attacking prey underwater or dealing with opponents during fights.
This is possible due to special muscles designed to retract the eyeball down into the socket (5).
Here’s a comparison of blinking functions in humans versus alligators:
| Function | Humans | Alligators |
|---|---|---|
| Moisten eyes | Yes | Yes |
| Remove debris | Yes | Yes |
| Protect from irritants | Yes | Yes |
| Shield eyes while attacking | No | Yes |
| Retract eyeball for protection | No | Yes |
As we can see, alligators utilize blinking in some unique ways that help them thrive in their environments. From keeping their eyes healthy to temporarily shielding their vision during hunting and fighting, blinking serves multiple important functions for these incredible reptiles.
References:
- https://www.floridamuseum.ufl.edu/discover-fish/sharks/vision/
- https://animals.mom.com/purpose-third-eyelid-reptiles-birds-10749.html
- https://www.bbc.co.uk/bitesize/topics/zx882hv/articles/zc2ydk7
- https://umm.edu/health/medical/ency/articles/corneal-abrasion
- https://animals.howstuffworks.com/reptiles/alligator-eyes1.htm
Other Interesting Facts About Alligator Eyes
Excellent Vision
Alligators have phenomenal vision both during the day and at night. Their eyes are specially adapted to thrive in aquatic environments. The eyes are positioned high up on the head, allowing alligators to see above the waterline when mostly submerged.
In addition, a transparent third eyelid helps protect the eyes when underwater. The pupils can constrict to pinholes in bright light or dilate widely in darkness. At night, a tapeetum lucidum behind the retina reflects visible light back through the rods, improving vision in low light.
This adaptation causes eyeshine, making alligator eyes glow red at night.
During the day, alligators have excellent color vision and visual clarity underwater. Their daytime vision is superior to a human’s, with at least 2 to 4 times greater spatial resolution. This allows alligators to spot small prey items from far away.
Under ideal conditions, an alligator can detect prey movement up to 30 meters away based on studies done at the St. Augustine Alligator Farm Zoological Park in Florida.
Third Eyelid
Alligators, crocodiles, and birds all possess a third eyelid called a nictitating membrane. This protective membrane sits inside the lower corner of the eye and sweeps horizontally across the surface to moisten and clean it.
Alligators can keep their eyes open underwater because the nictitating membrane covers and protects the eye like a built-in pair of goggles.
When an alligator attacks prey, the nictitating membrane also serves to shield the eyes from splashing water and debris. Similarly, if an alligator is dragged from the water, the membrane will cover the eye to prevent damage.
While the membrane provides protection, it does slightly impair vision in that eye while swept across.
Sleeping with Eyes Open
Along with keeping their eyes open underwater, alligators can also sleep with their eyes open! They frequently rest in the water with just their eyes, nostrils, and the top of their head exposed. This allows them to quickly react to the presence of prey or predators nearby.
Should a potential meal swim by, they can instantly strike. But if a threat approaches, they can dive below the water for safety.
Even on land, alligators tend to sleep with their eyes at least partially open. This is another defensive behavior to stay alert for predators. If conditions are extremely safe, an alligator may close its eyes fully to sleep. But usually their eyes remain open to some degree.
Conclusion
As we’ve explored, alligators do blink, but only at around a tenth the rate of humans. Their nictitating membranes allow them to moisten and protect their eyes while keeping them open to hunt prey. While alligator eyes appear unmoving, they are complex organs adapted for these reptiles’ aquatic lifestyle.
The next time you see an alligator’s eyes peering above the water, you’ll know there is some blinking going on behind the scenes! Understanding the unique aspects of alligator eyes sheds light on how these creatures have evolved for 200 million years.
