Because they can't fly, running and strong legs keeps them safe from predators.
No It can run fast but not as fast as an Adult.
Running birds e.g. Ostrich can run fast comparable to horse in a desert .
Ostriches run fast because of 'springy' tendons
Ostrich
Ostrich and Emu.
Gentoo Penguin
So it can escape from predators!
Ostrich
An ostrich can run 40mph and sustain 30mph.
I think why they can run fast is something to do with their feathers.
An ostrich is a huge flightless bird that can run fast. A pigeon is much smaller and can fly.
It is the Ostrich.