DecoLamb

I would also like to rebuttal this. A quarter horse is capable of hitting 45mph, and there is a couple sports that focus on going at high speeds while hitting sharp turns. These sports are barrel racing and pole weaving. Cheetah are also able to make some DECENTLY sharp turns while going 70mph after their prey. Which usually consists of Thomson's Gazelle [Who hit about 50mph] that zig zag like a mofo to escape these big cats. I would direct you to this video, that shows both barrel racing and pole weaving. As well as possible accidents that are plausible with these large birds. I would ALSO also like to add, as you said yourself, this is a fantasy world. Real logic does not apply for the most part. However, these creatures already SORT OF exist in the real world. Ostriches, emu, and the lovely cassowary. All of these birds can go at high speeds and ostrich can even be ridden and are raced. Also all of these animals can stomp your face in with little to no effort. Something to be said about mother nature. It doesn't like you and will invent all kinds of critters to wreck you.