Proboscis monkeys ruminate
Observations and video films revealed that the proboscis monkeys were chewing their food a second time. Animals were seen sucking in their abdomen to bring a bolus back into their mouth to chew again. The researchers suspect that these monkeys can eat more by allowing their food some time in the stomach before chewing it further. Because proboscis monkeys are quite heavy, the fruit and leaves they eat aren’t always of the highest quality: it has to come from branches heavy enough to support the animals’ weight. The juiciest leaves are out of reach. Rumination, it is believed, allows digestive enzymes to work longer to break down the food and make the nutrients available.
It should be noted that the researchers’ conclusions are not undisputed, as the bolus returned to the mouth has never been analysed. This analysis would be quite difficult to achieve, as these monkeys swallow their food quickly when approached.
There are cases of humans and gorillas regurgitating and chewing their food again, but this behaviour has been seen as pathological, whereas rumination in the proboscis monkey is adaptive.
Results of the study were published in Biology Letters.