Observe their be'avior. Take for a start the sheeps' tendency to 'op about the field on their 'ind legs. Now witness their attempts to fly from tree to tree. One thing is for sure, the sheep is not a creature of the air. They have enormous difficulty in the comparatively simple act of perchin'.
Trouble is, sheep are very dim.
Once they get an idea in their 'eads, there's no shiftin' it. E's realized that a sheep's life consists of standin' around for a few months and then bein' eaten. And that's a depressing prospect for an ambitious sheep. It is the sincere hope of the author that some day, the mother ship which was dispatched from planet Ovine to retreave the lost herd will arrive to take all of the stranded sheep back. You see, more than 15 milenia ago a space ship carrying a group of intergalactic explorers crashed on the planet that they named Earth.