Because it couldn’t fly over it. No matter how hard they flap their wings, chickens can hope for little more than a short glide and a soft landing. They aren’t really “flightless birds,” a group that includes ostriches, emus, and cassowaries. The breastbones of these birds can’t support the powerful muscles required to pump wings and achieve liftoff. (Penguins, meanwhile, are a different type of flightless birds built for underwater “flight.”) Flightless birds lost their ability to fly through evolution, but chickens became flightless over time through selective breeding, which made them too heavy for liftoff. After all, farmers hardly want their prized poultry soaring north for the winter. The chicken’s ancestor – the red jungle fowl, which is still around today – has retained the ability to fly.
Picture Credit : Google