Monkey chews its cud

Posted on April 3, 2011


Proboscis monkey in Borneo

This afternoon the Northerner and I took our dear Irish friends Mr D and Bodhráin-Queen (BQ) to the leafy and well-heeled area of Primrose Hill for a wander through the village before catching their flight.

Forget four-by-fours, the streets have become a hazardous place for  pedestrians with hordes of buggy-pushers on every street corner. To escape the ankle-bashing-crowd we dipped into one of the local pubs for a spot of lunch.

Over the din of well-spoken voices and clinking glasses, came the protests and screams of kids who’d much rather play with their food than chew it. At that age, can you really blame them? Their palettes have yet to develop and everything tastes the same because it’s usually smothered in Ketchup.

Kids, drunkards and bulimics aside (I never thought I’d group all of them in the same category) most primates, which includes people, will chew and then swallow food before we digest it. Regurgitating food is not something our bodies are built to do and long-term it can have serious health implications. You’re probably wondering where I’m going with this post. No, I’m not about to start dishing the dirt on some celeb I spotted hacking up in the loo, but I will apologise now for this rather unsavoury post – there is however a scientific reason for it.

In a paper published by researchers in the Royal Society Biology Letters they filmed the feeding habits of 23 free-ranging proboscis monkeys (Nasalis larvatus) in Borneo, South East Asia. For the first time, researchers found these monkeys were regurgitating and re-masticating their food. Usually famed for their pendulous and elongated Cyrano de Bergerac sized-Schnauze, the males vocalise by making a kee honk sound. Let’s hope they don’t make a barfing sound when they regurgitate.

Lead author Ikki Matsuda from Kyoto University’s Primate Research Institute, has just returned home to Japan from the field. He told me he was very surprised to see this behaviour and he’s been studying this species for almost 6 years.

He said: “The digestive tract of the proboscis monkey is drastically different from that of humans and great apes. The proboscis monkey has a distinct sacculated (chambered) fore-stomach where bacterial digestion occurs prior to the glandular stomach.”

Proboscis monkeys are found in the swamps of Borneo, they are also very good swimmers. The researchers collected their data from a boat on the river during early mornings and late afternoons from January 2000 to March 2001. There was one occasion where Matsuda went into the swamp, which he says was very scary because of the threat of crocodiles lurking in the mud, as well as having to deal with large spiders and leeches. It’s by no means a glamorous job.

Matsuda says they can only speculate why these monkeys feed like this, but says from the evidence collected it suggests that it allows the monkeys to eat more sooner. Proboscis monkeys predominantly eat plants, seeds, flowers and fruit and young leaves, he said: “The major advantage should be an increased particle size reduction of the digesta, which means the smaller plant particles can be digested faster by the fore-stomach bacteria.”

In other words, this population has the ability to eat like a cow! Ruminants, such as cows and other hoofed mammals, bring up food already swallowed back into their mouths by a contraction. The cud (food) is chewed for a long time before being swallowed again. With these monkeys, their abdomen would contract and it would then stick its tongue outside its pursed mouth. The regurgitated material stayed in the mouth and then the monkey puffed out its cheeks, re-chewed and swallowed the food for the second time.

But evidence that regurgitation and re-mastication occurs in this population does not make it gospel for all proboscis monkeys. Matsuda told me, “There is no basis on which to estimate the likelihood of the behaviour being regional or species-specific in a ‘global way’. We wanted to be correct – we have just investigated this one population. Therefore we wanted to state that we cannot make the claim of a ‘global’ phenomenon.

“Traditions (especially those related to feeding) have been reported in primates – like the macaques that wash food and even season it with salt water. We simply cannot exclude such a tradition. Given the fact that only one animal of the six was observed continuously. It could be that some animals learn this behaviour from parents/peers. We cannot say how ‘voluntary’ the behaviour is – we only have video evidence and that is not a scientific method that we can base claims on. We can only speculate whether this activity  is a ‘learned tradition’, some of us doubt that, or whether this is something that ‘happens to them’ due to their physiological mechanism.”

Hopefully this hasn’t put you off your Sunday roast, but it has given you food for thought.