The reload button toggles the glide off and on (always on by default) but beware! If you turn it off and gain fall speed, when you turn glide back on you will be slowed, but not 100% immune to fall damage anymore. You can still survive a fall from the skybox, if you have at least 200hp.
Most people think this chicken is useless but you can use the archaeopteryx to fly for an unlimited amount of time! Just have an argy (or any other flying creature) on follow with a low following distance and when it is low on stamina drop from your bird and go back on it after a few seconds.... your bird is now full of stamina!