I once rode a pteranodon to land another pteranodon who had dropped me in mid air. You know how they just hover in that same spot when that happens. So I reached her altittude and whistled so she started following me. Now after I landed, I disabled following and she wasn't following me but every time I'd mount my other pteranodon she'd start hovering around. Took me a while to figure out she was following the other pteranodon, not me