Food consumption and energy budgets of the giraffe.
To estimate the efficiency of foraging strategy, the rates of food intake of adult giraffe in the Serengeti National Park are assessed. Daily energy intakes derived from the diet are compared with estimates of the energy requirements for year-round reproduction. The reproduction performance of giraffe in the Serengeti is discussed in the light of such energy budgets. Giraffe are exerting a major impact upon the development of the Acacia regeneration, removing up to 85% of the new shoot production. The browsing impact varies throughout the year, being greatest in the dry season when production rates decline. Such high offtake rates are the result of a disequilibrium in the browse production-consumption system caused by the double perturbation of elephant impact and the reduction of fire. There is no short-term evidence that the giraffe impact is curtailing plant productivity, and it is suggested that Acacia species have evolved a high resilience to browsing as a result of the positive selection for tolerant genotypes. The daily rates of food consumption, 1.6% and 2.1% of the liveweights of adult male and female giraffe, are similar to other ruminants. However, the quality of the diet, assessed in terms of crude protein levels, is consistently higher than that of African grazing ungulates, particularly in the dry season, when the protein levels of the browse diets show only a marginal decline. The energy budgets suggest that giraffe can maintain a positive energy balance throughout the year and during most stages of the female reproductive cycle. Any possible energy deficit during the post-partum lactation phase is avoided by the selection for browse of high energy content, especially in the dry season. The foraging strategy adopted by giraffe enables the animal to attain the metabolic threshold for year-round breeding.