Me and some friends were talking the other day about how strange it can be to see something sleeping with its eyes open.
This is something that a lot of animals, including humans, seem to do, and why it occurs is an interesting phenomenon.
Indeed, it’s even a very common aphorism among us humans—sleeping with one eye open.
This does imply we associate it with a heightened level of safety. Our assumption, then, was that prey animals must do this to heighten their awareness.
What about goats, then?
Do goats sleep with their eyes open?
No, goats don’t sleep with their eyes open. Goats sleep with both eyes closed, and though they might seem slightly open, they are closed for the most part. Goats do not keep half of their brain active while asleep as many species do. Goats sleep with their eyes closed.
Sleeping with eyes open might be a selective advantage for some species, but goats seem to have gotten along just fine without it.
Rather than keeping eyes open or their brain alert, goats are simply very light sleepers, and are easily woken by the sounds and disturbances a predator might make.
Let’s look further into this.
Will goats sleep with their eyes open?
No, they won’t.
What certainly is true is that goats will sleep very lightly.
This, on top of the nature of their herd existence, is essentially their main threat protection apparatus for the nighttime.
When asleep, goats are very easily woken.
Whether that is by another member of the herd who happened to be awake alerting them to danger, or by the predator disturbing the environment.
So, goats do not need to sleep with their eyes open.
Indeed, most species that do so do not do so in order to be able to better detect danger.
Often, it goes hand in hand with what is called unihemispheric sleep.
This means that one-half of the brain is able to remain alert during sleep.
But this is not about detecting threats.
It is reserved for things like marine mammals who need to surface for air, birds on long flights, and some reptiles.
These are generally not about threat detection, but merely about energy efficiency.
Goats do not have this problem, so they’ve no need to be able to keep half of their brain alert, and thus their eyes open or partially open.
But can they?
Can goats sleep with their eyes open?
Again, no.
Closing the eyes is a necessary part of sleep.
As I said, there are times in a goat’s life when it may appear to be sleeping with its eyes open.
Kids, for instance, often appear to be doing this.
In order to get to sleep and stay asleep, though, a goat needs to close its eyes like most mammals.
Shutting out the external stimuli is a vital step, especially for an animal like a goat with its rectangular pupils.
Those pupils are able to take in a much greater panorama than ours are.
When trying to sleep, though, this excess of visual stimuli makes it virtually impossible to fall asleep this way.
The other important point to make is about the cycles of sleep goats go through.
Do goats have REM sleep?
Yes, they do.
But before we look at this, what is REM sleep?
Mammals and other animals go through cycles of sleep during each night.
REM sleep is typically the deepest of those cycles, and stands for Rapid Eye Movement sleep.
This is because your eyes are literally dashing about rapidly beneath your eyelids.
Goats also go through these cycles, and REM sleep is necessary to get the full rest.
It is at this point that a goat, and indeed a human, may appear to be sleeping with their eyes open.
Their eyes, darting about rapidly, may shift the eyelids somewhat.
This is often seen in kids, so let’s look at stages of the goat’s life.
Do kids sleep with their eyes open?
Again, the simple answer is no.
They don’t have the capacity or reason to do so.
However, it is often at this age that they appear to be sleeping with their eyes open.
This is again due to that cycle of REM sleep.
A younger goat can often be a lot more restless in its sleep, and so its eyes may jut open more than older goats would.
However, the simple fact is that they still do not and cannot sleep with their eyes open.
Do bucks sleep with their eyes open?
Just to put to rest any final doubts, no, mature bucks do not sleep with their eyes open.
Their eyes will be closed, and that is the only way they’ll be able to get to sleep.
As they’re more mature, as I said, you will find they are very light sleepers.
You may be convinced your goat saw you and that was what woke it up, but in fact you probably just made a noise.
It doesn’t take much to wake them from their sleep.
So, as you can see, the simple answer is no, goats do not and cannot sleep with their eyes open.
At different stages of life, it may appear as though their eyes are open while they sleep.
Certainly, for kids, during particular cycles of sleep, their eyelids may be fluttering a great deal more, making it appear as though they’re sleeping with their eyes open.
In reality, though, animals needing to sleep with their eyes open, or at least with their brains active, is limited to a few fairly specific evolutionary niches.