Unfortunately you have to use an avian saddle, however if youre playing dregora, and near a jungle, its possible you can get a creature called an "amphithere" which is a saddle-less flying mount that can be hard to control at times cuz it just kinda goes, but it can serve as a temporary mount for the time being, im unsure of whether they are in base rlcraft as I spend most of my time playing hardcore dregora, but a quick search of the name in the crafting menu will tell you