Experienced bow hunter recalls being scared by an unknown scream/howl near Austin

The witness had climbed down from a deer stand during bow season and waited at the base of the tree after hearing movement in the brush assumed to be deer. After it became too dark to shoot, a very loud high-pitched scream or howl lasting several seconds occurred very close to his left. He jumped up and ran about a half-mile to the road and reports he has not returned to those woods since.