Evidence for the occurrence of rumination-like behaviour, or merycism, in the koala (Phascolarctos cinereus, Goldfuss)

Abstract

This paper provides the first account of merycism in koalas (Phascolarctos cinereus), and in doing so, potentially sheds new light on the occurrence and significance of this behaviour in other herbivorous marsupials. Koalas fitted with acoustically sensitive transmitters, to monitor mastication and ingestive behaviour, were also found to make bouts of rhythmic ‘mastication-like’ noises that were not associated with ingestive feeding events. On average, these bouts consisted of 9.16 ‘mastications’, at an average rate of 1.21 ‘mastications’ per second, and occurred 53.3 times throughout a 24-h period. Furthermore, bouts were usually preceded by, and always followed by, a series of ‘creaky’, guttural noises that were interpreted as regurgitation and re-swallowing, respectively. Merycism may allow koalas to periodically re-masticate gastric digesta, while in a resting position, and thus potentially save energy and increase the extent of food preparation. Consequently, merycism may contribute to the koala's ability to consume a high fibre, poor quality diet.