Feeding and Chewing Behaviours of Nubian Ibex: Compensation for Sex-Related Differences in Body Size

Abstract

Size-related differences in digestive capabilities are thought to account for patterns of diet selection, social structure and habitat use by small- and large-bodied herbivores. We examined food processing behaviours that could compensate for digestive constraints resulting from the relative scaling of metabolic requirements and gut capacity with body mass. We observed feeding, chewing and ruminating behaviours of sexually size-dimorphic Nubian ibex fed diets chopped to a short (1-2 cm), medium (8 cm), or long (25 cm) length. These diets differed in the amount of oral processing needed for particle size reduction, bolus formation and swallowing. Food particle size did not affect intake rate (g/min) but chewing investment (chews/g) of both sexes was 30% less for the shortest hay. Rumination activity of both sexes approximated the maximum sustainable level of almost 10h/day for all diets. Chewing rates (chews/min) during rumination did not differ between males and females. Chewing investment of females was 40% greater than that of males while feeding and more than 50% greater while ruminating. Size-related differences in molar occlusal surface area (∼ 15%) were much too small to account for sex-related variation in chewing investment. Our results support the hypothesis that females enhanced digestion rates relative to those of larger-bodied males through increased oral processing.