In the ancient times, army officers observed sacred chicken before going to a battle. The sacred chickens were given grain and if they ate it, the battle commenced, if they didn't, the armies withdrew from fight.
See the story of the Battle of Drepana for referece.
"[...] some sources claim that Pulcher performed the inspection of the omens before battle, according to Roman religious tradition. The prescribed method was observing the feeding behaviour of the sacred chickens, on board for that purpose. If the chickens accepted the offered grain, then the Roman gods would be favourable to the battle. However, on that particular morning of 249 BC, the chickens refused to eat – a horrific omen."
Also see from 4:50 in this Academy Award winning education animation on birds by Disney https://www.youtube.com/watch?v=al_Zxx6HUG0