Spider Monkeys and Woolly Monkeys Frolic with each other

Anthony Di Fiore, a primate biologist at New York University, writes from Ecuador, where he is using GPS technology and camera traps to study the behavior of male spider monkeys.

Monday, Jan. 10
Here at the station they are saying that we brought the rain with us. After two virtually bone-dry weeks in late December and early January, it has been alternating between drizzle and full-on downpour since we arrived, punctuated by just a few hours of sun here and there. At night, lying in the cabins, we can hear rain rattling for hours on the corrugated aluminum roofs, drowning out the typical nighttime chorus of frogs and insects.
Despite the rain, it’s been a great three days of monkey follows. We’ve checked in on radio-collared groups of woolly monkeys, sakis and titis. But most of our time has been spent making sure that all of the spider monkeys in our main study group (called MQ-1) are all still around. MQ is our abbreviation for maquisapa, the word in the Indian language Quichua for spider monkey that translates (appropriately!) as “big hand.”
Although spider monkeys live in large social groups, you only rarely see more than a handful of animals at a time traveling or hanging out together. Instead, you run into subgroups consisting of one or few females and their offspring, a set of patrolling males or a male-female consorting pair. Subgroups join together and split apart frequently, leading researchers to describe the pattern as “fission-fusion” sociality. This kind of social system is rare among primates — indeed, it’s rare among mammals generally. A short list of mammals that live in fission-fusion groups would include chimpanzees, muriquis, elephants, some social carnivores and a few cetaceans.

A Long Journey Into the Ecuadorean Forest

.In three days, we’ve already found about half of the individuals in our group, including three of the six adult males and six of 11 adult females. MQ-1 contains about 32 individuals, counting the kids, and occupies a home range of about 600 hectares. Each hectare is 100 meters square, or roughly the equivalent of two American football fields laid next to each other, so this is a huge area to explore. But we’ve become pretty good at thinking like the monkeys over the past few years, so we can narrow our search by focusing on the routes that the monkeys commonly use to travel their range and by checking out the feeding trees that we know they like and that are currently fruiting.

Today, we checked out a huge Clarisia racemosa tree in the heart of the group’s range. Clarisia, from the same family as figs, produces fleshy, scarlet-colored fruits with a single large seed. It’s a favorite of the spider monkeys, which will pick and swallow dozens in a single feeding session. Sure enough, 30 meters up in its spreading crown we found the female Sofia (named after my older daughter), who was the first spider we learned to recognize. Sofia was with her latest two kids, Silvi (a female, born in late 2005 and now an impish adolescent) and Summer (a tiny male, born in the summer of 2009). Also nearby was a large group of woolly monkeys that soon began feeding on the Clarisia, too. With the woollies in the tree, we had to move back to avoid the fusillade of half-eaten strawberry-size fruits raining down from 30-plus meters.

The high point of the morning’s observations came a few minutes later when the feeding frenzy ended and both species of monkeys retired to the surrounding trees to rest and digest. With her mother and brother resting in the crook of a tree above her, Silvi approached and began bouncing around a couple of smaller woolly monkey juveniles. They responded by getting up and following Silvi as she scrambled up some lianas (woody vines), threw herself into the thin crown of a subcanopy tree, and then clambered back to repeat the whole process. It turned into a rare, long bout of interspecies play, with Silvi and the woollies chasing one another back and forth for 15 minutes or so until the woolly group moved off.
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