From a psychological/behavioral perspective, what are some reasons a horse would go out alone better than with a group? Being herd animals, why would going solo into unfamiliar territory somehow calm a horse?
I am the handler/rider. I enjoy group riding as much as solo riding, so that is not the influence. The horses in the group are seasoned and calm. I am a very active rider, not a passenger, and I don't let his attention drift or let training issues slip by unnoticed. I work them then and there. Since he was prone to act up on group trails, it never occurred to me to try my horse alone, expecting it would be 10 times worse. I've since discovered he's calm as can be and does exactly what is requested when we are solo.
Background: My horse is nine. He was abused in his youth, started poorly and ridden much too young. All he knew was trails with a group. He was insecure, confused, uncoordinated, and extremely spooky when I got him five years ago. He was also herd-bound. I restarted him and worked him systematically through all of his issues. I noticed years ago that when I hand-walked him in unfamiliar territory with another horse (there to calm him), he would be hyper-reactive and put on quite the show. When we were alone, he wouldn't. It didn't make sense, so I assumed it was the influence of another variable I hadn't considered.
I know how to train the issue. I'm stumped on the why, as it goes against everything I've ever experienced and understand about a herd animal. His vision has been checked and is good. Some insight would be greatly appreciated.
The answer is likely that your horse is a politician! Horses, being herd animals, have specific “rules of the road” that involve subtle cues like ear position, head height and body position in relation to others. I suspect your horse is overly sensitive to these cues, which has made for a feedback loop that has increased and/or sustained his anxiety when around other horses. He is likely spending most of his time either fretting that he is not in front, or fretting that he is not in back (or next to a particular horse).
I would suggest taking a step back to see if there are opportunities to reward calm behavior around other horses and observe the triggers that seem to increase his arousal. If he is not pastured with other horses, I would recommend trying to pasture him with others to help him associate being around other horses with relaxation.