The feeding ecology of Coke's hartebeest, Alcelaphus buselaphus cokei Günther in Kenya

Despite a wide distribution through Africa, the genus Alcelaphus has been little studied. The aim of the work described here was the study of a population of Coke's hartebeest in the Athi Plains of Kenya, which included the Nairobi National Park. It was designed to complement existing information on the species' behaviour and to examine the interactions between the hartebeest and their food supply. The approach, both in the field and subsequently, is also described in Ch.1. In Ch.2 I describe the methods which are referred to frequently through later chapters. These include the field methods of counting and ageing hartebeest, the location of study areas and the sampling of vegetation, the measurement of rainfall and the collection of specimen animals. The organisation of the resulting data and their analysis are described.
Descriptions of the Athi Plains are few. Their geology and topography are outlined in Ch.3, while Ch.4 concerns their climate, with the emphasis on rainfall as the most important seasonal parameter. The vegetation of the Nairobi Park and the rest of the plains is then described (Ch.6) at the level of the vegetation zones for the whole plains (1850 km2) and of vegetation types for the study areas. The Nairobi Park is shown to have a very varied vegetation despite its small size (114 km2).
In Ch.6 the sizes and distributions of the populations of hartebeest and other numerous herbivores are described from aerial censuses over the plains and ground counts in the park. This establishes that the density of hartebeest in the park is 6.6 times that of the plains. The latter population also contains significantly fewer adult females and young above the age of 1 month. The hartebeest in the plains show very minor population movements compared to either wildebeest or zebra, and exchange with the park population is infrequent. Using information theory methods, Ch.7 serves to define the niche of the hartebeest in relation to those of other herbivore species, and to compare the structure of the communities of the two areas. The herbivore community of the plains also includes cattle, sheep and goats. The results of this ground-work confirm the sedentary existence of the hartebeest population, but show it to occupy a relatively wide variety of vegetation zones through the year, occupying many vegetation types and tolerating a broad range of grass standing crops. Compared to other species, the hartebeest shows a very marked seasonal occupation of vegetation types in the park, but this is not apparent in the plains. The same methods are extended to measure the similarity between species' distributions, and the cases of high overlaps are examined using published information on the feeding habits and diets of the species. Considerable ecological separation can be inferred between all species- pairs except between hartebeest and zebra in the park in the dry season, and between hartebeest and cattle in the plains in the wet season. The distributions of the latter pair in the dry season, also, suggest their ecological equivalence.
In Ch.8, starting Part II, I describe the hartebeest's diet and its seasonal changes from the analysis of rumen contents. The hartebeest grazes exclusively. Its diet is described in terms of its content of grass parts, rather than grass species, amongst which Themeda triandra is shown by various sources to be predominant. The effects of the differential digestion of these parts in the rumen are reversed by applying a correction factor based on specific gravity (Appendix 12) to obtain the diet proportions. In the wet season the proportion of leaf in the diet is higher than in the sward, while the less nutritious stem is under-represented. When the leaf in the sward has been depleted in the dry season, the hartebeest no longer exercise any dietary selection. Comparison of these results with those published for zebra show that the parts taken by the 2 species are very different in proportion, and I conclude that this would result in their ecological separation even when feeding together. On the other hand, comtemporary evidence on cattle diets, also from the Athi Plains, shows them to be taking the same diet as the hartebeest, and evidence is presented that Themeda is also frequently eaten by cattle. Their coincident distributions are parallelled by similarities in their rumen morphology and bacteriology, with both classified as the only "bulk roughage grazers" in the Athi Plains community.
The method developed for the correction of grass part proportions in the rumen to those in the diet allows the daily dry matter intake to be calculated from the weight of dry matter in the rumen (Ch.9). Intake varied between 26 and 87 g/kg.W.73.day in the dry and wet seasons respectively, through the effect of the water content of the food on its specific gravity and subsequent behaviour in the rumen. The calculated variation in intake with the succulence and quality of the food is consistent with experimental observations on the factors controlling the intake of coarse feeds by domestic ruminants. The calculated intakes are similar to those of 42 and 34 g/kg.W.73.day of an experimental hartebeest and sheep, respectively. A regression method for predicting the hartebeest's intake under field conditions from the faecal nitrogen content is developed.
In Ch.10 the dry matter intake is converted into the intakes of protein and energy, and the gain to the hartebeest of selective feeding is calculated. Selection appears capable of increasing the digestible crude protein intake by 50%. The calculated intakes are compared with maintenance standards for domestic ruminants and are shown to have fallen below the maintenance levels in the dry season of September 1972. Calculation of the intakes uses information from a feeding trial with hartebeest and sheep, whose intakes were also measured. The experimental hartebeest's metabolisable energy intake was 51.5 kcal/kg.W.73.day, which was considerably lower than the measured metabolic heat production of 116.1 kcal/kg.W.73.day of another tame animal. The metabolisable energy intake of the sheep of 45.1 kcal/kg.W.73.day suggests that the lower metabolic rate may be more correct, and further supporting evidence is presented.
Chapter 11 is the first of 3 chapters in which the hartebeest's energy expenditure is considered. The daily activity patterns are described from day and night observations in the wet and dry seasons. Little seasonal variation in the regime of 3 feeding periods at nearly equal intervals through 24 hours was apparent. The total times spent feeding was 2 hours shorter at 8.6 h/24h in the dry season than the wet. About half of this reduction was made up by an increase in the time spent walking, associated with the need to visit water sources in the dry season. Further observations showed that males drank every 3 days, females every 2 days. The energy cost of this activity was almost the same in both seasons at 52% greater than the basal metabolic energy expenditure.
The use of energy for growth and the deposition of body reserves is considered in Ch.12. The shot animals showed that full adult body weight is not reached until the fourth year, after which weight appears to decline immediately. Using a photographic method the external condition of territorial males was shown to depend on the rainfall over the previous 4 months. Non-territorial males were always in significantly better condition. The shot hartebeest were characterised by very small kidney fat reserves which showed no seasonal variation. Marrow fat varied seasonally, as did the weight of a selected muscle, representing the protein reserves of the body. The latter also changed through age, parallelling the changes in total body weight. The significance of these findings is discussed in the light of the low fat content of tropical ungulates, the hartebeest's slow growth rate and its possible adaptiveness.
The small surpluses of energy ingested by the hartebeest and the small body reserves lead to a discussion of the female reproductive pattern (Ch.13). First breeding occurs in the fourth year. Calving occurs in every month of the year. The timing and size of the birth peaks allow the conclusion that nutrition and female condition are the ultimate and proximate factors influencing reproduction. The adaptiveness of this system to a fluctuating, equatorial environment is discussed.
In Ch.14 the utilization of the resources of food and water of the park are considered. The hartebeest's seasonal use of the vegetation, mentioned in Ch.7, is described, and is shown to be clearly defined and predictable. The data necessary for a causal analysis of the grazing cycle were not available. The quantity of standing water in the park study area is shown to depend on the rainfall over the previous 2 months. Only under exceptional conditions does animal use make significant inroads in to the water resources. Comparing this study area with those in the plains, the abundance of water in the park is due to the construction of dams rather than to any greater water-retaining capacity. In the dry season, the hartebeest aggregate around the remaining water sources. This provides evidence additional to that in Ch.11 that the hartebeest conserve energy by reducing their activity when experiencing sub-maintenance intakes in the dry season. The significance of this to the distribution of the hartebeest in the plains is discussed.
In the final discussion (Ch.15) the ecology of the hartebeest is compared with those of several other species. Most notably, the hartebeest differs from the related wildebeest by being more sedentary, eating a poorer quality diet, growing more slowly, reaching sexual maturity later, but calving as often as conditions allow, followed by a high calf survival rate. In their "opportunistic" reproduction and prolonged mother-offspring bond, the hartebeest resemble some of the desert marsupials. The relationship between cattle and hartebeest is considered in more depth. Their ecological equivalence (Chs.7,8) is shown to lead to their competition both through exclusion on the part of the cattle, and exploitation for the same food. The hartebeest is the competitively inferior species, and their density and lower proportion of young animals in the plains are identified as the results of this interaction. Archaeological and historical evidence confirms that similar habitat selection by Bos spp. and Alcelaphus spp. has occurred over a long time throughout the African continent. Finally, the reasons for the predominance of the hartebeest in the park since 1961 is discussed, and it is concluded that the high densities observed in 1971-72 were not unusual in historical times. The management practice of burning the park's vegetation has allowed further increases in numbers, while the large numbers of cattle in the plains have caused the reverse.