Food intake rates of herbivorous mammals and birds and the influence of body mass

The bite size and bite rate of an animal determines its food intake rate. Because of the importance of ingesting food, this behaviour makes up a large part of the daily routine of mammalian and avian herbivores, since they have to ingest large amounts of fibrous forage to meet their daily energy demands. Hence, they have to solve the dilemma of conflicting interests in their daily activities between foraging, social behaviour, sleep or predator avoidance. In this study, the role that body mass (BM) plays in this context was quantified and mammals and birds were compared regarding the influence of BM on instantaneous food intake rate (IFIR) (the first minutes of a meal), bite size (BS) and bite rate (BR). Because birds do not chew their food, it was hypothesised that they can increase their IFIR above the upper limit of similar-sized mammals which chew their food. Combining our own findings with literature, results showed that there is no difference between mammals and birds regarding IFIR, BS and BR. It was shown that IFIR (mammals BM0.95, birds BM0.82) and BS (mammals BM0.83, birds BM0.87) increase with increasing BM. Moreover, the factor 'non-chewing' does not increase the IFIR of birds.