Thrihyrne

I don't have my copy of The Hobbit with me, but I have a vague recollection of a bit of the Mirkwood scene where the company hears the sound of a hunt. Now, the only hunt that they would be likely to hear would be a chase, not a stalk, ie on horseback. Also the forest near the Elf-King's stronghold was more open and traversable, so horses would be able to run reasonably easily. Anyway, we have no idea how old Legolas is or where he's been or what he's done in the past, so he could have learned to ride anywhere. Or he could be a total novice, just using superior Elvish communication and balance skills to deal with the horse.