The Moa-keeper takes a ride on Iti the South Island giant Moa! Quite fun on a hot summer day.
However, that begs the question. Could you actually ride a moa? Well, it's complicated. Most moa were a shorter than a person, and you probably couldn't ride them. Thus, we have to stick with the biggest individuals, which are females of the genus Dinornis, the Giant Moa. They could grow up to 2 meters tall at the hips, and could crane their necks to 3,5 meters. They could look an elephant in the eye. So they are big enough to ride. They are also very robust in structure with wide hips and large feet, making them quite stable steeds.
However, there's a problem. Bird bones are pneumaticed, even those of the biggest Moa. This means that the bones are full of airsacks and have a honeycomb-like structure. And while this adds strength and keeps the bones light, they are very bad at bearing additional loads, unlike the heavy and rigid bones of large mammals. People riding ostriches isn't a good idea because reasons, as ostrich bones really aren't built for that kind of use.
So could you ride a Giant Moa? Maybe. But you really shouldn't do it. But if you insist, just don't do it often. That's how the Moa-keeper does it, anyway.