Elephants have always posed problems to authorities, either as crop raiders, major agents of habitat change or as a potentially valuable natural resource. Decision-makers have had to consider such diverse questions as whether elephants should be culled as an ecological management policy within a park, or whether anti-poaching forces should be reinforced and the ivory trade banned to prevent their elimination. The true status of elephant populations has been confused by their apparent over-abundance in some areas and their disappearance from others. In every case where decisions must be made, knowledge is required of how many elephants there are and how their numbers are changing.