When your usually well-behaved horse tenses up, gets spookier than usual, or fights your attempts to hold him back on rides through woods, he hasn't overdosed on "stupid" pills. Instead, he's reacting to the surroundings with:
Prey-animal vision. Simply put, your horse doesn't see the way you do. Your eyes, set in the middle of your face, give you a natural ability to focus on the narrow trail ahead and keep peripheral distractions to a minimum. But because of his evolutionary status as a prey animal, his eyes are on either side of his head, giving him relatively poor straight-ahead vision but excellent wide-field vision necessary for spotting predators.
Dense woods eliminate the wide field (and complicate matters with changing patterns of dappled light). This makes some horses extra-anxious about what might be coming out of those woods--and extra-spooky because of it. They can be extra-defensive, too, kicking out at horses that approach them from the side or behind.
Prey/herd-animal instincts. So why does your horse fight to get up close to the horse ahead of him when you're going down a wooded trail? Easy. Though your horse might have been raised far from anything resembling a herd imperiled by lions, tigers, or bears, he still inherited a prey/herd animal's instincts. To him, "safety in numbers" and "running with the herd" aren't clich?s. They're deeply ingrained survival strategies--so much so that all foals are born with instinctual knowledge that they must travel as closely to their dams as possible.
The inborn urge to follow others closely, for safety, doesn't disappear once a horse becomes an adult. It's something trail riders must work to overcome with further training and eventual habituation to the wooded-trails environment.
This article originally appeared in the August 2010 issue of Horse & Rider.