I have seen both horses and dogs learn a behavior by watching another of their kind with a human.
One time I was at the ranch teaching a horse to stand on a pedestal on command, and there was this one mustang who always stood at the fence and watched us. Every day I would work with this horse and the mustang would watch without ever looking away. A while later we let the mustang into the arena to run around and roll. First thing she did? Yup! Stood on the pedestal and looked at me without ever having learned it before.
Naturally, they can learn bad behaviors, too. A dog who has always been well behaved could start barking just because she has been hanging out with a dog who barks a lot. Or start chasing rabbits…
This group learning can be a great time saver when it comes to training. You have a couple of animals that know the rules, know how to do something, and all of the new ones will learn from them! For example, some cowboys and vaqueros will have their horses line up along the corral fence and face outward so that they can easily rope their horse of choice. This was taught to a herd of horses a long time ago, and now they never have to teach it to a horse again!
They just picked it up because the rest of the herd was doing it. So it gets passed on down the line.
Another good example is with my pack. I have a command to tell them to go to their places (a big bed they all pile on to). My dogs know this rule and do a really great job doing it, and now my new dog knows it! I never taught it to him, but he just followed the dogs on to the bed and heard me say the command. After two days, I told him to go to the bed, without any other dogs around, and he turned around and trotted to his spot. How cool is that? No training needed and how practical is that…
Of course learning in groups is how all animals learn anything, but I always find it interesting when they observe another animal and a human and figure something out because of it.