Comparative foraging behaviour and associated energetics of impala and blesbok

(1) The blesbok has a shorter daily feeding time than the impala, associated with its efficiency as a bulk feeder in contrast to the selective feeding strategy of the impala. (2) Blesbok are less sensitive to temperature extremes than impala, which are relatively more active during low temperatures and more dependent upon shade during high temperatures. (3) Blesbok fed almost exclusively on graminoids while the diet of impala was more variable but included a high proportion of dicotyledons. Faecal protein reflected this difference and was higher in impala than blesbok. (4) The blesbok has a greater rumen capacity and intestine length relative to body size than the impala, apparently in relation to the lower digestibility of the forage it consumes which necessitates a longer transit time in the gut. (5) Water requirements of the impala are greater than those of the blesbok. (6) It is concluded that the life strategy of the blesbok emphasizes energy conservation while the impala maintains a more energetically costly lifestyle. This results in a greater dependence by the impala on food of high quality which it obtains through selective feeding and seasonal dietary flexibility. The blesbok adjusts its energy expenditure to compensate for seasonal variations in quality of its diet.