Diet and Lifestyle

Diet for a Small Primate by Stephen F. Ferrari 

Buff Head

Look at my buffy head!

The buffy headed marmoset of Brazil rely on plant gums for a large portion of their diet. These gums contain a variety of nutrients like carbs, protein, mineral slats and calcium. Using gum has two restrictions, however. The first is that gum is not produced in abundance by plants, and second, the breaking down and digesting of the polysaccharides within the gum requires a specialized gut and specific bacterial flora for fermentation.

To obtain gum from the plants, many “gummivores” have developed claw-like nails that allow them to move over the gum producing plants easily. They also have specialization of the cecum (an offshoot of the intestines) where the gum is fermented; and they have long rough tongues that allow them to reach the deep gum deposits in insect holes. Their main source of gum is that acacia plant. The marmosets harvest gum by gouging holes in the bark, but they never gouge all the way around the trunk, which would kill the plant. They regularly return to the same holes on a small selection of available acacia plants. Using the same sites over and over has a number of advantages. By using the same plants and holes, they spend less time and energy gouging. Marmosets also eat insects, and use the holes these insects bore to exploit even more gum sources.

Despite the large amount of gum and insects they ingest, the buffy headed marmosets prefer fruit, which they get to eat two months out of the year – Jan. and Feb. AKA the wet season. During this fruit eating time the acacia gum and insects aren’t neglected completely. This is good, because gum provides high levels of calcium and insects are rich in phosphorus. On average, the buffy headed marmosets are only active for about ten or less hours a day. During the night, to reduce their metabolic use, they enter slumber similar to that of hibernating animals.

Marmoset societies are matriarchal. It was once thought that breeding was limited to one dominant female per group, but this has now been refuted. Depending on the individuals present for breeding and the size of the group, the number of breeding females changes. The marmoset groups are stable because of the relatedness of individuals. All members of the group invest in the care of the infants.

Marmosets are flexible in their diet (eating fruit when available and adjusting their diets accordingly) and in their mating systems (group composition and the availability of potential mates are key factors in how many females breed).

Monkeys with Inflated Sex Appeal by Sue Boinski 

Normally, squirrel monkeys are small bodied and the males can not be distinguished based on size.

Squirrel Monkey

However, starting a few months before female squirrel monkeys are in estrus, the males start to swell up. Water becomes deposited between the skin and muscles on the shoulders, back and upper arms (Did you get your tickets to the gun show?) This is not due to increased or decreased food intake, and it is not related to reproductive ability because males are fertile year round. The enlargement is due to testosterone being converted into estrogen (i.e. the female reproductive hormone). The more testosterone a male has, the more estrogen he produces, and so the bigger he gets. The swelling is due to an altered water balance (the same thing that causes some women to gain water weight at the end of their menstrual cycles). The biggest the males get is at the peak of breeding season – leading researchers to believe that it is a product of sexual selection, and therefore increase mating success (females choose the largest males to mate with).

Because of the way squirrel monkeys move through the forest, they are prime targets for flying predators. Normally, female squirrel monkeys are solitary creatures – however, when they have babies, they band together and are more vigilant than normal. Naturally this leads to greater welfare for all the children involved. Babies born before and after the “peak” of births are more likely to be killed by predators.It would therefore be in the best interest of all the normally solitary females to give birth at the same time, and to do this, they would need to be in estrus at the same time.

Since the ladies band together when they have their babies (and not at any other time), why would they even bother caring about who is the biggest male? Two features of the biggest males: 1. they have often been in the troop the longest and have resisted challenges from outside males 2. the enlarged males are vigilant throughout the year (moreso than others) and are more likely to intervene to save threatened babies. So maybe the ladies are just hoping that by maybe mating with the vigilant, intervening guys, they will be more likely to protect their children. Or perhaps they choose big males to mate with to produce big sons, who will then in turn mate more when they are older.

squirrel monkey


Menu for a Monkey by Karen B. Strier

Compared with the other primates in this post, the Muriqui are pretty large. The largest monkeys in the new world, actually. But they have a pretty slow metabolism, which lets them live off leaves for a large part of their diet. Since they have a slow metabolism, you would expect them to be slow moving creatures – but they aren’t! They swing like crazy through the branches, which is obviously a energetically costly way to travel. To make it worthwhile, the Muriqui use this fast travel to procure energy rich fruits.

A Muriqui

The muriquis are an aggression free species, and the sex relations are egalitarian. The males and females are similar in size, and males do not compete among each other for mates, because the females are free to choose who they like, even the peaceful males. So why expend the energy fighting? All of this seems to stem from the diet of the muriqui. Because they sometimes have to rely on just leaves, the males and females are both large (little sexual dimorphism), and the long-distance fruit hunt requires agility which limits how big the males can be.

Even though the leaves the muriqui eat make up a large chunk of their diet, they always prefer fruits and flowers (who wouldn’t?). Finding fruits and flowers is the main catalyst behind their far ranging journeys. If the fruits and flowers are scarce, the muriqui go out and find them, even if they have to go faster and further than they have before. Why expend all this energy when there are so many leaves around? Why not just eat those? Well even if they did love leaves as much as fruit, it wouldn’t help them. They have a fast digestive system that doesn’t allow them to subsist on leaves alone. (This also works to their advantage – they don’t have to worry about being too choosey with leaves. They can eat leaves with tannins and toxins and don’t have to worry about absorbing them.) Fruits are easier for them to digest and are a better source of energy and nutrition.

Diet of the muriqui also influences their reproductive habits. From late September to the middle of October, the monkeys choose to eat leaves of two legume plants instead of the abundant fruits. In doing this, the males and females acquire a lot of protein which prepares them for the mating season just around the corner. At this same time of year, the muriqui also go to the outskirts of the forest to eat “monkey ear” – the fruit of a legume plant. Monkey ear contains stigmasterol, which is a steroid used to synthesize progesterone. Some recent studies have shown that plant hormones can regulate the reproduction of some animals, so maybe stigmasterol is being eaten at this particular time period to increase fertility in the muriqui.

Night Watch on the Amazon by Patricia C. Wright

Owl monkeys are the world’s only nocturnal monkey (all other nocturnal primates are prosimians). They have giant eyes, and look like this:

“I look weirdly like a cat!”

and here is a picture of just their skull, so you can see how big those orbits really are:

The skull of an owl monkey

Look at those peepers!

Different from most noctural mammals, the owl monkeys can still see color, and also lack the reflective shield on the retina  – which interestingly suggests that their ancestors were daytimers! If this is so, what would have made them do a complete 180 and start functioning at night?

Daytime presents more threats, for one. Eagles, harpies, and hawks love to eat little monkeys, including our friend the owl monkey. The threat of being eaten was not the only driving force (though, it would have been enough for me). By foraging at night, the owl monkeys don’t have to deal with other species – who are bigger, badder, and stronger – competing for the same food. They can eat at night with no interruption or harassment. Great idea, owl monkeys! You would think that other monkeys would follow suit, since it’s working out so well for the owl monkeys. But they have not. Mainly because we lost that reflective layer (the tapetum) and we have pretty bad vision at night. The owl monkey, though, has developed large eyes which help them in their search for night food. But since they, too, have lost that reflective layer, it can only help so much. On unclear nights, the monkeys stick to the same paths and move slower than normal, indicating that they too are affected by low lighting.

We’ve seen how diet affects many parts of these monkeys lives. Is there any part of our diet that you think influences us in a similar way? (i.e., reproductive habits..etc?)


3 thoughts on “Diet and Lifestyle

  1. The owl monkey reminds me a lot of myself upon entering university. Prior to my undergraduate experience I ate three meals every day, at a pretty set time. Moving to a college town and not being limited by the availability of food at specific times [i.e., my mom wasn’t making my dinner, I could take a lunch break whenever I wanted, etc…] and not having my meals chosen for me [more or less] my eating schedule went all crazy- Fourth meal at Taco Bell anyone? While I may not have become completely nocturnal in my eating habits, twenty-four hour availability of a huge variety of foods has delimited the way I eat.

  2. I love food. I think food affects numerous aspects of our lives. I tend to associate certain foods with certain holidays, certain family members, certain vacations, etc. As far as reproduction is concerned- who are you going to sleep with? They guy who takes you out to KFC or the one who takes you to a swanky, upscale restaurant? No contest.

  3. I agree with Elizabeth– there are definitely some foods that correspond with high status and some that correspond with low status. If you are looking for ways to gauge the elite status of your potential mate, food might be a good indicator! And from Emma’s blog we know that status is important when choosing a mate.

    Also –I think of my college diet when reading about the marmosets rather than the owl monkeys. They are flexible in their food choices based on what is available. In college, especially at the dining hall, healthy options can be somewhat limited. And if they are available, may not be of very good quality. Maybe this is me making excuses for the “Freshman 15” but I was more likely to grab a slice of pizza and head to the library than making up a whole salad with dressing and utensils and other fancy things– I’m not trying to cart all that around campus! Sure, this is food choice based on convenience rather than season… but it seems like the same idea?

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