before vowels ornith-, word-forming element meaning "bird, birds," from combining form of Greek ornis (genitive ornithos; plural ornithēs) "a bird," in Attic generally "domestic fowl, cock or hen," which often was added to the specific name of the type of bird, from PIE *or- "large bird" (see erne).
For "bird" Greek also had ptēnon (plural peteina), related to pteron "wing," from the root meaning "to fly."
word-forming element of Greek origin meaning "divination by means of," from Old French -mancie, from Late Latin -mantia, from Greek manteia "oracle, divination," from mantis "one who divines, a seer, prophet; one touched by divine madness," from mainesthai "be inspired," which is related to menos "passion, spirit" (from PIE *mnyo-, suffixed form of root *men- (1) "to think," with derivatives referring to qualities and states of mind or thought). Compare mania.
<a href="https://www.etymonline.com/word/ornithomancy">Etymology of ornithomancy by etymonline</a>
Harper, D. (n.d.). Etymology of ornithomancy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/ornithomancy