Smithsonian magazine has a long profile article about my UW-Madison colleague Karen Strier: "Humans would be better off if they monkeyed around like muriquis". The article gives a lot of details about the biology of muriquis, Strier's long-term study subject, and provides great context about how a generation of primatologists abandoned many of the assumptions that guided the field's origins and forged a new way of looking at behavioral ecology.
The most interesting current research from Strier's field site has to do with the way muriquis are adjusting to demographic change -- including changes in the sex ratio, higher population density in a forest remnant, and use of the ground:
Though northern muriquis are critically endangered, the population in Strier’s study site, which is protected from further deforestation and hunting, has increased. There are now 335 individuals in four groups, a sixfold increase since Strier started her study.
That’s a development worth celebrating, but it’s not without consequences. The monkeys appear to be outgrowing the reserve and, in response to this population pressure, altering millennia of arboreal behavior. These tree-dwellers, these born aerialists, are spending more and more time on the ground. At first the behavior was surprising. Over time, though, Strier made some sense of it. “They’re on an island, with no place to go but up or down. When humans didn’t have enough food, they invented intensive agriculture. Monkeys come to the ground. It makes me think of how hominids had to eke out an existence in a hostile environment. Our ancestors would have brought to that challenge the plasticity we’re seeing here.”
Small population of primates, multimale groups, increasing population density and new use of the ground. That's such an interesting combination when we think about hominin origins.