I have shot one charging due to coming too close - he was molested by lions some time before - he charged without any second thoughts...been on the track of others - seemed to me that (when they are unaware of you and they are not buggerd by lions or other meanaces the night before) they always need at least 2 confirmation from different sences to take a gap i.e. - they won't fly if they see you (their adrenaline is allready pumping up tho), but afer receiveing the second conformation of your presence (smell or sound) they depart