Population dynamics of elephants in Etosha National Park, S. W. A. /Namibia

Abstract

Abstract provided by author:

Elephant numbers in Etosha National Park have increased steadily since the recolonization of the park by elephants in the early 1950's. A period of rapid increase occurred from 1979 to 1983, coinciding with the recent Trans-African drought. The population appeared to have erupted and was culled twice to halt further increases and prevent irreversible changes in plant species diversity due to an over-population of elephants. This study was done to determine fecundity and mortality schedules and the rate of increase of the elephant population, in order to manage the population by artificial control of numbers

Six aerial censuses at four-month intervals from 1983 to 1985 showed that the number of elephants in the park varied between seasons, and both the dry and wet season populations declined after 1983. The rate of decline, as also the rate of increase from 1973 to 1983, was higher than expected from fecundity and mortality rates. Age structures of herds were determined by aerial photogrammetry and did not change substantially from 1983 to 1987, and from 1977-1987 when using ground observations. Fecundity rates determined from females culled in 1983 and 1985 were higher than in populations elsewhere in Africa, in contrast to the observed decline in population size in Etosha National Park. Survival schedules based on the age distribution of females indicated higher mortality rates than in other populations. The relative importance of mortality factors was determined from carcase records, and anthrax proved to be the single most important cause of death in all age groups except calves, where predation by lions was more important

Evidence from reproductive parameters, age structures and mortality schedules along with recorded movements of elephants in and out of the park, suggest that changes in abundance were not due to explosive breeding or mortalities before and after the drought respectively, but to immigration and emigration. Elephants moved freely in and out of the park as determined by rainfall and human disturbance, and the Etosha National Park population appears to be part of a regional population of elephants occurring in north-western SW A/Namibia, including parts of the Kaokoveld, Ovambo and Kavango