Snakes are a very real danger to horses; only dead broke horses don't fear them. Otherwise, wild horses and what's called "green broke" horses will avoid them. However, there are accidents where the horse doesn't see/smell the snake or the snake just feels that a curious horse simply got too close. These are fatal mostly from venomous snakes -- Rattlesnakes, Cotton mouth, etc. -- not garden snakes and such.

Think of it this way: Horses are natural fright-and-flight animals. If they feel something is dangerous -- even a RAKE -- they will by all means run from it. (I've seen a horse fright at her own lead rope, which she sees every day.)

Coyotes don't hunt in packs, but a coyote could very well take on a newborn foal (when the mother is tired and weak) or a sick horse. Same for wolves; wolves will never attack something in full health -- it's too dangerous for the pack.

As for wolverines, I could see that happening.
"The wolverine has a reputation for ferocity and strength out of proportion to its size, with the documented ability to kill prey many times its size." ( http://en.wikipedia.org/wiki/Wolverine ) However, as you can clearly read, you're not about to find a wolverine in the Cimarron Territory; it's far too hot for these subarctic creatures.

As stated before, a bear probably wouldn't attack unless it was:
a.) Threatened young.
b.) Sick or starving.
c.) A mother bear simply protecting her cubs; bears are famous for attacking, even if the victim isn't a threat to the cub(s).

Think about the beginning clip of the movie: What animals did you see? Bald Eagle. Bears. Deer. Bison.

Another very real danger to wild horses is OTHER HORSES. A stallion of another herd or band will outwardly attack foals, and has been documented, even when unprovoked. (If you Youtube search "Stallion Meets Newborn Foal," you will find information that will suffice.) While the stallion Looking Glass may have done the handicapped foal a favor by killing it, the video proves that carnivores aren't the only dangers that wild horses have to face.

Actually, a wolverine would pose quite the threat for a foal or a young horse. These animals never stop growing, it's how their body works. Many range to the size of medium dogs and outweigh many. They have 5 inch claws and their bite force is out of the roof. There have been reported kills of a wolverine killing a sick/old elk. They don't live in packs, they are solitary animals, and what makes them a threat to horses would be if the horses were in wood-land areas since these weasels climb trees an like to jump down on their victims back. It would be very interesting to see a story were one of these nasty-attitude creatures are a threat to SOME horses.
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Wolves is the same old same old. They go for the weak, the old and the new, not much of a story of that.
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Bears could attack and kill a horse but.. they might just be too lazy for it. Unless one of the horses killed a bear cub, then the mom will strike revenge. They normally avoid herds in general and keep to carcasses, elk, deer, berries and lots of salmon.
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If the snake is poisonous and gets enough venom into the horse's bloodstream then it's byebye horsie. It all depends on how much venom, how strong the venom is, and where it strikes the horse. But this wouldn't be an attack to eat, it would be in complete and total defense.
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Annndd prairie dogs... nyeh i don't need to say more xD

http://ic2.pbase.com/v3/21/495621/2/48418328.Wolverines.jpg Here's a pic of a Wolverine, just so you can see what they look like.

Prairie Dogs- http://bills-earth.com/pdogs/pdogfamily.jpg

There is no snake large enough to swallow a foal in the United States the only threat they pose is the ones who are venomous biting a horse.

http://thevoiceofthehorse.com/predatorprey/ It looks like a pretty good site for your information, but I don't know about Prairie Dogs probablly wouldn't harm a horse very much, but it's hard to tell. You can't predict it, but I know for a fact that wolverines would kill a horse in a heart beat. Now bears can rip you to shreads, but a horse deffinatly would NOT die without a fight! And in the end, a bear would probablly win after all. Wolves aren't much of a threat, but I think that they could probablly severely injur a horse really, really, really bad. About cats and lions and lynxes and stuff, you do know in the movie hoe that puma/cougar attacked Spirit. I know it would be original to write about, but it wouldn't be STEALING. I mean, snakes are very harmless creatures if you think about it. They're at the middle of the food chain. They could easily swallow a new born foal, like Sierra said. So, I hope that helps! And you're are perfectly welcome. Bye!!!

Thanks Sierra! I vaguely remember prarie dogs being rodents now - like I said, I have no idea of waht American wildlife is like. There's no way they would harm a horse, but the burrow thing was interesting - I wouldn't have thought of that. As for the birds, I didn't mean so much as carrying off (although that would be hilarious!) but maybe having a peck/scratch or eating a carcass.
Charming.
Makes sense about the snakes, but poison is poison - very useful.
Wolves; I believed they would be capable of taking down horses, I've just never heard of it. But wolves became extinct over here hundreds of years ago, so they're another animal I have little education on.
So yeah, thanks for the answer. I think that should be enough for anyone wanting a bit of variety as far as dangers go, but if anyone has any more feel free to post!

Wolves were capable of taking down horses and preyed on them often, but were extensively hunted by prejudiced humans to near extinction, however, in remote areas of the west and north they were able to survive. So wolves would be feasible as predators.

Prairie Dogs are basically a large species of rodent which lived in large family groups or "towns" they are not predators, but their holes were dangerous due to horses stepping in them and breaking their legs. A horse with a broken leg is a death sentence.

Wolverines are member of the weasel family, but resemble long-tailed bears. They are very dangerous to humans and other smaller animals but would pose no threat to horses they would be too small and even a foal could escape from them.

Bears wouldn't be too dangerous to adult horses but would probably go after foals or yearlings.

There is no bird in the united states large enough to even attempt to carry off a horse or any animal of the same size. (and they seem to be on the same side as the horses') I don't see why a bird would attempt to even try such an endeavor unless it fell out of the nest as a chick

Snake-Bites (mostly from rattlers) are lethal to horses, but mostly because the horse got too close to the snake or stepped on it making it feel threatened, half of the time the horse didn't even know it was close by the snake until it bit it. Snakes wouldn't go after a horse for any other reason.

Coyotes (part of the dog family but are much smaller) would go after newborn foals.