In the late 1960s, there were approximately 35,000 elephants in the Tsavo ecosystem (40,000 sq. km). This population has suffered two population crashes. The first was the drought in the early 1970s when an estimated 6,000 individuals died and over the next 4 years with low rainfall and lack of vegetation a further 3,000 died.
The majority of these deaths were females and young elephants. Unlike pregnant females, females nursing a calf or young calves, independent bulls were able to travel greater distances in search of vegetation and their mortality was lower.
The second crash was due to the killing of elephants for their tusks. The large bulls who survived the drought were the first victims for their large and heavy tusks. When the remaining bulls were difficult to find, the large females were targeted (their calves died as a results) and then whole families. By the late 1980s, at the height of the ivory poaching era, about 6,000 elephants remained in the entire Tsavo ecosystem.