I'm working on a pretty detailed alternate history of the ancient America's, and currently I'm focusing upon Mesoamerica in particular. The core difference is that, through several different mechanisms that can be handwaved away, the Natives at the time were able to domesticate significantly more animals than they did in true history.
One of the animals I'm eying for domestication, mostly for the cool factor, is the Kelenken. These birds were huge, nearly 10ft tall carnivores that went extinct a long time ago, significantly before any human presence in the area. I'm willing to handwave this as well, since it's decently plausible that a much smaller relative could be domesticated towards gigantism to bring them back in line with this size. For the purposes of this question, it's fair to just assume we're dealing directly with the Kelenken species, for simplicity.
However, a big issue that I'm running into is a rational reason for why the Natives would bother interacting with these large carnivorous birds long enough that they would be domesticated, and ideally a cool enough use for them.
I'd considered mounts, but birds-- even flightless ones-- are fragile and difficult to ride, and in this world the natives domesticated the Hippidion for riding anyway.
Then I thought about their potential as hunting partners, but humans brought dogs with them across the Bering Strait when they migrated to the Americas in the first place.
I don't really want them to just be another source of food, and eating a carnivore would be a waste of resources anyways.
I feel like I'm out of options here, but the idea of large domesticated carnivore birds is just too cool to give up!
How can I realistically justify the expenditure of time and resources towards domesticating the Kelenken species for pragmatic ancient humans?