Note on elephant mortality in Ruaha National Park, Tanzania.
In the Tanzanian National Parks rangers are paid a bounty for every tusk which they find in the bush and bring into Park H.Q. The date and weight of each tusk is recorded in the found ivory register. This note describes an analysis of the Ruaha National Park found ivory register for 1973-77. The register for the previous years was not available.
The found ivory comes from fresh carcasses, old carcasses and ivory recovered from poachers. Poached tusks accounted for only two of the records. From the register it was not possible to distinguish between ivory from fresh carcasses and ivory from old carcasses. Tusks may lie for some years in the bush. Assuming a constant level of elephant mortality, one would expect a constant number of tusks to be found per unit searching effort. Therefore, a change in the number of tusks per patrol can be assumed to reflect change in the number of elephants dying.
Ruaha National Park has a tropical semi-arid climate (Bjornstad, 1976) with one wet season and one dry season each year. The wet season lasts from December to April or May, and the dry season from June to November.