To get a bird’s eye view of the park, we have to compete with the vultures that alight amid plastic sacks in the makeshift neighborhood dump. Young men loiter across the way in front of a dilapidated shack that passes for the corner bar. The valley below shows signs of incursions by poor families like the ones who have mounted the favela that surrounds us on higher ground.

This is a homecoming for Murilo Drummond. Two decades ago the professor of genetics and evolution began to visit this area. At the time it was one of the few remaining sections of Amazon rainforest within the city limits of São Luís, capital of the state of Maranhão with close to a million inhabitants. Drummond frequently brought students on field trips and led research expeditions. Back then this dump replete with vultures was relatively pristine.

In 1980, 3,200 hectares were set aside as Bacanga State Park after being a Water Protection Area since1944. Much of the city’s drinking water comes from reservoirs inside the park. In theory, the park designation further restricted human settlement and activities in the area.

Population growth in Maranhão stands at 1.5% a year. As elsewhere in Brazil, affordable housing remains scarce. So instead of trying to address the incursions, public officials periodically whittle down the size of the park to reflect the new human settlements. The original 3,200 hectares have already been scaled back to 2,800.