Can horses only see sideways?

Because some people seem to think this: No.

Horses do see a much wider range than we do and have only a relatively small area of binocular vision, but they can see where they are going well enough to be able to, you know, jump.

How quickly do a horse's eyes adjust?

This came up in a Youtube video I was watching. Horses have considerably better night vision than humans. They can see in what we would consider pitch darkness, and I've misjudged things on the trail before and had to let my horse find the way home.

The price horses pay is that their eyes do not adjust well to sudden changes of light. The modern horse is a plains animal for much more of its evolution than we are. We still have a lot of features of a diurnal forest dweller, so our eyes are designed to handle light changes very quickly. That 30 to 60 seconds it takes for your eyes to adjust to a rapid light change is pretty quick.

A horse's eyes don't adjust nearly that quickly. In fact, a horse's eyes can take anything from 15 to 30 minutes to adjust. As plains dwellers, they aren't naturally adapted to patterns of light and shade the way we are. Their much better night vision also requires more time.

For writing purposes?

Horses will tend to spook when going from light to dark and vice versa. To a horse, a dimly lit barn door is a black cavern and even if they go in and out of that barn all the time...they will at the least hesitate, especially if they don't properly trust their rider or handler. Cross country course designers often intentionally put fences in the shade as a test of trust between horse and rider. Riding home after dark tests this trust in the other direction.

There have been incidents of horses running into objects, or each other, because lights in their pasture compromised their night vision.

Horses are going to be more vulnerable than human riders to light-based attacks - flares, light spells, etc. If you are fighting a mounted person on foot, tossing a simple globe of light spell at the head of their horse could be incredibly effective.

(And what if elven eyes work like this too...)

Can horses track people by scent?

I didn't watch it, but apparently this happened in Tangled.

So, here's the best answer I can give.

Horses have a fantastic sense of smell. If a horse comes across a pile of manure, they will try to sniff it, and I suspect they can identify who "dropped" the poop that way. They can certainly identify predators. As for following a trail - I've never seen it, but I've heard anecdotes that some horses will. As horses are grazing animals, they have no "need" for the skill of tracking, but they do need to be able to identify what they're smelling. And horses do like to get the scent of a new person much like dogs do.

So the answer is: They can, but seldom actually do.

Can horses really smell fear?

It's a trope that a horse can "smell your fear" and may act up as a result.

The truth is that horses absolutely can tell when a handler is afraid. Some horses will act up. Others will actually try to calm the fearful person down (the best lesson horses).

However, there's no evidence they do this by "smelling" your fear. It's vaguely possible that domestic horses can pick up on and identify human fear pheromones...but this is not normal across species.

So, how do they tell?

Horses can easily read the body language of another horse. Domestic horses readily learn to read human body language and tactile cues - that's how we train them, after all.

Horses can't smell your fear - but they can feel the tension in your muscles if you're riding them, see your body language if you aren't and also hear your heart rate. It might seem that they're smelling your fear - actually, you're telling them you're afraid in signals that might as well be shouting in "horse."

(If you're handling or riding a horse and think it's picking up on your fear, try slowing your breathing - which will help both of you calm down).

Do Horses See In The Dark?

Horses have much better night vision than we do. They have a tapetum lucidum - a reflective layer behind the retina which is seen in most mammals other than primates.

Although they can't see in total darkness, horses can safely navigate in forest on a moonless night. They can manage quite happily if left to their own devices in an enclosed arena all night with no lights, without walking into the walls or each other and ending up injured.

The downside is that equine eyes do not adapt to sudden light changes as quickly as ours do. It's not uncommon for horses to spook or start when entering or leaving the barn (or a trailer) on a sunlit day. Also, horses can easily be dazzled by flash photography - it's not recommended to use flash close up with horses. (Fortunately, modern cameras can take some quite nice pictures without flash in fairly low light, especially if you have a tripod).

For writing purposes - a character who gets benighted in the woods might be able to drop the reins and trust the horse to get them home. (I've personally been on a horse in light where I would have wanted a flashlight if walking and just let the animal handle it).

Do Horses See Color?

A lot of people assume that horses, like dogs, are color blind.

This is not true. Horses do, in fact, see color. They do not, however, see color as well as we do.

Horses have, in fact, dichromatic vision - they see the world the same way as a human male with red-green color blindness. They have particular difficulty distinguishing between yellows and greens - but they see various shades of green very well.

This all makes sense for a herbivore who needs to be able to quickly identify various plants.

The tradition of painting show jumping fences bright colors is actually to make sure the horse can see them. "Natural" obstacles are more challenging to horses.

More on equine vision tomorrow.