Population Ecology and Response to Cropping of a Hippopotamus Population in Eastern Zambia

Does Mortality Impact Negatively on Hippopotamus (Hippopotamus amphibius) Population Size and Density in Luangwa River, Zambia? A Historic Perspective

“…Heavier culling would result eventually in an increase in calf production through decrease in calving interval and age in puberty. There was an indication that the latter occurred during the earlier study in the 1970s by Marshall and Sayer (1976) when 5 percent of females in the seven to eleven year age group were pregnant in 1970 and 20 percent in 1971. These data may, however resulted from the marked difference in rainfall that occurred in the two years; the rainfall in 1970 -1971 was double that of 1969 -1970.…”

“…It was the biased sex ratio in favour of females that promoted increased recruitment after culling. Studies on the impact of culling on hippopotamus population in the Luangwa valley by Marshall and Sayer (1976) found a rate of increase of 4.3 percent per annum, which was derived from data for the Nsefu area (blocks A-C: Figure 1) where annual counts were carried out from 1953 to 1966, which later increased to 5.8 percent after culling. The mean age of puberty for females also declined leading to more prevalences of pregnancy and increased births after culling (Sayer and Rhaka, 1974).…”

“…Studies conducted by Lock (1969) in Queen Elizabeth National Park and those by Attwell (1963) in the Luangwa valley, suggested that early burning appeared to induce more traveling for feeding purposes which increased stress on the animals which also exposed them to predation. In Kafue National Park for instance, hippos were concentrated in pools near available food, and ten animals were found dead in 1970 either killed by lion or intraspecific fights (Marshall and Sayer, 1976). Indeed the loss of food supplies due to man induced fire regimes at the critical time of the year might in it be a major factor in controlling density and not disease per se, (Mashall and Sayer, 1976).…”

“…Loss of pasture to fire reduces the food base for the species and reduces its body resistance to environmental stress. Under such circumstances, disease comes in as a secondary factor, taking advantage of the nutritionally deprived individuals (Marshall and Sayer, 1976).…”

“…Historical data on the Luangwa hippopotamus population including that by Marshall and Sayer (1976) showed that poaching was the main factor that caused population decline in the late 1800s and early 1900s. In Luangwa valley, hippopotamus population increased greatly since 1939 after poaching was put under control and no disease incidences were mentioned as a major factor at that time (Attwell, 1963).…”