Cotton-top tamarins: punk rock primates

 

I met my first cotton-top tamarin as a 19-year-old student at the University of Wisconsin. Little did I know that I would spend the rest of my life trying to protect this exceptionally cute, exceptionally rare little monkey, which, in the wild, is restricted to a tiny corner of north-west Colombia.

 

Today, I’m back in the field, on a tropical dry forest trail near Santa Catalina, about an hour from Cartagena. I’ve followed this track at least 100 times, trying to avoid being eaten alive by mosquitoes and ticks. I also keep an eye out for the venomous fer-de-lances that lurk at the path’s edge.

 

The closer I get to Tamara’s group, the louder the beep from our radio-tracking equipment. Pacho, one of my team, is wearing a transmitter in a backpack-style harness. It’s a good thing we have these gadgets to locate our elusive study subjects; otherwise, we’d walk right past them.

 

 

Amid the din made by the forest’s cicadas and crickets, I hear a familiar noise: tamarin chirps. Most people think that they sound just like bird calls, but with experience you can tell the difference.

 

Cotton-tops have more than 40 vocalisations, used to communicate about everything from the discovery of food to the approach of predators. Fortunately, these are ‘G’ chirps, indicating that the (as-yet hidden) tamarins are merely curious and want to investigate the new arrival in their territory – me.

 

Looking up into the canopy, I finally spot Tamara, the cotton-top that has provided us with so much new information about the lives of these amazing punkish primates.

 

Like the rest of her group, which I have been watching for more than nine years, she is used to the presence of humans, allowing me and my team to get wonderfully intimate views of the rifts and alliances that are part and parcel of tamarin politics.

 

 

Cotton-top families typically consist of an adult male and female, together with their offspring. But there are always exceptions, and that’s what makes the social dynamics of tamarin groups so hard to understand.

 

Tamara’s story is interesting. She was evicted from her group when a new female seized control from her mother, Sara. Tamara and Sara wandered the forest looking for another group to join, and eventually formed an alliance with two males, Pacho and Reinaldo.

 

Everything seemed fine until Sara gave birth to twins, which Tamara promptly kidnapped. She wouldn’t let Sara nurse the babies, and repeatedly chased her mum away.

 

Then Pacho and Reinaldo weighed in, forcing Sara to abandon the group altogether. Tamara became the dominant female and has remained so ever since.

 

I’m not sure what happened to her mother; I once saw her with several nasty bites, perhaps the legacy of a failed takeover attempt elsewhere.

 

 

Understanding the factors that influence reproduction and group living in cotton-top tamarins is important. But how do you study the reproductive cycles of diminutive, 0.5kg monkeys that live about 20–30m up in the trees?

 

Our solution was to start gathering faecal samples from the forest floor, from which we could extract hormones to establish the females’ ovarian cycles.

 

Cotton-tops feed mostly on fruit (they are major seed dispersal agents for many trees and other plants) and have a rapid gut transit time. They often defecate when they wake in the morning or after a nap: we simply watch for the ‘tail lift’ that signals a sample is on the way.

 

The dung is collected, stored in freezers, then processed to work out the reproductive profiles of the females in our study groups.

 

 

Our research has found that each tamarin group has a single sexually active female, who gives birth once a year between April and July. Afterwards, the female is reproductively suppressed and does not begin to cycle again until five to seven months later, when she will conceive on her first or second ovarian cycle. But what about her daughters?

 

Though female cotton-tops are technically sexually mature at 10–14 months, they do not usually exhibit ovarian cycles that could result in conception, unless a new male arrives.

 

This radically changes the group dynamic: the young females now become fertile, creating competition between mother and daughters for dominance. Squabbles break out and the proverbial fur flies.

 

Tension escalates until one of the females leaves or is ousted, or the group splits into two separate bands. Under more stable circumstances, young females will leave at two to four years of age. 

 

Tamara holds the record for the longest reproductive tenure in any of our study groups: nine years. In this time she has produced a remarkable eight sets of twins (twins are the norm in cotton-tops), plus one single infant.

 

Females are pregnant for six months and babies weigh about 15 per cent of their mother’s body weight. That’s equivalent to a nine-stone woman giving birth to two ten-pound infants.

 

 

When there are youngsters around, it’s an exciting time to watch cotton-tops. Each member of the family plays a specific role in the lives of the new arrivals. Whereas in most primate societies infant care is primarily the mother’s responsibility, with these monkeys everyone helps out in some way.

 

In fact, the dominant male and the oldest animals in the group spend the most time carrying the infants – the mother holds them only to suckle. Thanks to the youngsters’ strong gripping reflex, they can cling on to the backs of their carers as they leap through the forest at breakneck speed.

 

Newborn infants are tiny, with long tails that they curl under the bellies of their carers. However, within a week, the shock of white hair on top of their heads starts to emerge and their dark coats are visible.

 

At 5–10 weeks of age, they begin to make their first independent forays away from their carers. They will jump off the back of one animal and climb onto another.