Change in Population Number and Reproductive Rate of Elephants in Uganda

Abstract

Four aerial counts of elephants (Loxodonta africana) on a 1,500-square-mile area, including the southern two-thirds of Murchison Falls National Park and vicinity, Uganda, were made from July, 1963, to May, 1964. The average number of 6,750 elephants was about 1,000 below the average counted in the same area in 1958-59. An unusually long dry season between mid-June and early November, 1963, caused an early movement of elephants from the grasslands of the study area to the woodlands outside. With the onset of rains in late November, elephants began moving back to the study area. They continued this movement into the December-March Dry Season, concentrating near streams and in unburned woodlands of green vegetation. During the March-May Rainy Season major migrations occurred. The highest count was enumerated at this time and elephants were widely distributed. On two adjacent areas to the north (Tangi-Karuma area and the Elephant Sanctuary) three aerial counts indicated similar distributions and seasonal movements. However, data from four aerial counts in 767square-mile Queen Elizabeth National Park in southwestern Uganda showed different seasonal distributions and movements: 1,758 elephants in the June-August Dry Season, 1,329 in the August-November Rainy Season, a further decline to 1,295 in the December-March Dry Season, and an increase to 2,222 in the March-May Rainy Season. Annual increment varied inversely with population density. The highest increment (8-9 percent) was in Q. E. Park where the average density was 2.2 elephants/square mile and restrictions on migrations are minor. The next highest annual increment (7-7.5 percent) was on the combined Tangi-Karuma area and the Elephant Sanctuary, north of the 1,500-square-mile study area. Here the average density was 2.8 elephants/square mile and migrations have not been appreciably restricted. The lowest annual increment (6-6.5 percent) was obtained on the 1,500-mile study area where density averaged 4.5 elephants/square mile. It is here that drastic changes have occurred to distribution of elephants, and serious restrictions have been imposed on their migratory behavior. Results of 12 aerial counts of elephants, conducted between January, 1957, and August, 1959, on a study area which included the southern two-thirds of Murchison Falls National Park, Uganda, were reported by Buechner et al. (1963). In the present report, results of four aerial counts on the same area, conducted between July, 1963, and May, 1964, are presented primarily to show the changes that have occurred in number and annual increment of elephants during the past 5 years. We also conducted aerial counts north of this study area and in Queen Elizabeth National Park, Uganda, for comparative information on numbers, annual increment, seasonal distribution, and migratory behavior of elephants. We hope that this information, by emphasizing the deleterious effects of an excessively dense population, will provide a basis for better management of elephants in these and similar areas of East Africa. Definitions of the terms family unit and herd follow those given by Buss and Smith (1966:376). The term group refers to any coordinated assemblage of elephants not identified as belonging to a more specific category. A concentration is defined here as a loose and uncoordinated assemblage of elephants occurring as singles or any combination of categories. We are grateful to the New York Zoological Society for providing funds to conduct most of the aerial counts. The Uganda National Parks and the Uganda Game Department contributed supplementary funds that allowed us to include the northern areas (Tangi-Karuma and the Elephant Sanctu-