The Life Of Birds 1. To Fly Or Not To Fly (9 of 19)

The Life Of Birds

If pursued, it can sprint at over 40 miles an hour.
But although it is now flightless, it still has many of the physical characters evolved by its ancestors that enabled them to fly.
It still has feathers and they are still placed on its wings in much the same position as those on the wings of a flying bird.
But they are now useless for flight.
Their filaments have lost their hooks so they can no longer be zipped together into an unbroken blade.
Instead they are loose and fluffy.
Their only function now is as insulating blankets, to keep out the cold at night and the heat during the day.
0striches have become grazers, the bird equivalent of antelope or horses.

But unlike them, they not only pick up leaves.
They swallow all kinds of other things as well, and for a very good reason.
Just as they inherited feathers from their flying ancestors, so they also inherited a lightweight, horny beak instead of a heavy jaw laden with teeth.
And without teeth, they need another way to grind up their food.
A pebble can help them do just that.
Down it goes into a muscular compartment of the stomach, the gizzard, a kind of mill where bits of vegetation are churned around and ground into a digestible pulp.
But while some birds were abandoning flight, some mammals were becoming formidable hunters.