Antelope are funny critters. You can pretty much predict the reactions of whitetails and mulies. But an antelope is capable of surprising you. Sometimes you'll come upon them and they'll stand at fairly close range and just stare at you, as if they couldn't care less what you are or what you plan to do. Other times they won't let you get within half a mile.
I saw several today and they were all skittish, like this little lady who clearly didn't want her portrait made.