FEEDING AND CHEWING BEHAVIORS OF NUBIAN IBEX - COMPENSATION FOR SEX-RELATED DIFFERENCES IN BODY-SIZE

1. Size-related differences in digestive capabilities are thought to a ccount for patterns of diet selection, social structure and habitat us e by small- and large-bodied herbivores. We examined food processing b ehaviours that could compensate for digestive constraints resulting fr om the relative scaling of metabolic requirements and gut capacity wit h body mass. 2. 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 i n the amount of oral processing needed for particle size reduction, bo lus formation and swallowing. 3. Food particle size did not affect int ake rate (g/min) but chewing investment (chews/g) of both sexes was 30 % less for the shortest hay. 4. Rumination activity of both sexes appr oximated the maximum sustainable level of almost 10 h/day for all diet s. Chewing rates (chews/min) during rumination did not differ between males and females. 5. Chewing investment of females was 40% greater th an that of males while feeding and more than 50% greater while ruminat ing. Size-related differences in molar occlusal surface area (similar to 15%) were much too small to account for sex-related variation in ch ewing investment. 6. Our results support the hypothesis that females e nhanced digestion rates relative to those of larger-bodied males throu gh increased oral processing.