From Halopedia, the Halo wiki
The space owl is an avian creature native to an extraterrestrial world. Concept art appeared implying its inclusion in Halo Wars, meaning it would likely be native to one of the planets visited. It was intended to act as what Ensemble Studios refers to as ambient life, or wild animals meant to make the environment seem more realistic. Ensemble Studios jokingly referred to it as resembling a Phoenix, such as the bird depicted on the UNSC Spirit of Fire's insignia. It was cut with the rest of the alien wildlife from the final release of the game.
The owl has two large wings, a small head, and tail with two curving feathers. The head is also located midway up the body, not on the top (though this may be a result of a "humpback shaped" body), with two feathers flanking the top of the body. The name of this species presumably means extraterrestrial owl, rather than an owl that lives in space.