A northern muriqui mother perches in a tree with her new infant and juvenile son
During this past winter break, I worked 12-hour days in one of the last remaining fragments of Brazil’s Atlantic Forest. This 2,400-acre protected forest reserve is situated on a coffee plantation near the Brazilian city of Caratinga. It is also one of the only places where the critically endangered northern muriqui monkey can still be found.
When I first came here to study muriquis more than three decades ago, virtually nothing was known about their behavior or ecology, or what it would take to ensure the species’ survival. It took years of observations to decipher their exceptionally peaceful, egalitarian society, which distinguishes the northern muriqui from nearly all other primates.
Muriquis are the largest New World primates (except for humans), and they live correspondingly long lives. Some of the original individuals present at the start of my study are now in their late 30s, if not older. There are grandmothers and even some great-grandmothers; I have known them for more than half of my life.
Their long lifespans put a premium on survival over reproduction, at least in terms of the population’s resilience to local environmental fluctuations. Yet it is still a great thrill every time an infant is born.
The birth of any infant, and especially a female, bodes well for the future of the population, which has grown from 50 to 361 over the past 32 years, and now represents more than one-third of the entire species.
Such a rapid population recovery could be regarded as a rare example of a conservation success. However, forest regeneration in areas surrounding the reserve has not kept pace with the muriquis’ expansion, and they now live at one of the highest densities known.
By studying the muriquis’ responses to these natural population pressures, we are gaining insights into their behavioral flexibility and ability to adapt.
One of the muriquis’ first responses was to expand their use of vertical space by spending increasingly more time on the ground. Here, they can benefit by supplementing their diets with fallen fruits and other food sources they can’t reach from the trees, as long as the risks from terrestrial predators, such as ocelots and pumas, remain low.
We know that human ancestors made a more permanent shift from a tree-dwelling to ground-dwelling way of life. Although muriquis are quite distantly related to us, the same kinds of pressures driving the muriquis’ ground use might have also been involved in our own.
An even more extreme response by the muriquis to the increasingly crowded conditions has been the emigration of females into a neighboring forest fragment outside the protected reserve.
Over a four-year period, at least six females risked their lives by crossing open fields to reach another, unpopulated forest. These females are showing us that they need more forest, and are leading us to the areas they have chosen. We now know where to establish the connecting corridors that will provide safe passage for other muriquis into the new forests, so their numbers can continue to grow.
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