Visitors to the Philadelphia Zoo look at a young orangutan climbing in the Great Ape Trail. (Matt Rourke/AP)

Batu, a Sumatran orangutan who will be 3 years old on Oct. 2, loves her new playhouse: a 200-foot-long trail that hangs high above the heads of visitors to the Philadelphia Zoo. She can sit in a swing, hang from a fire hose, and play hide-and-seek with her mother. She especially loves to grab handfuls of wood wool, which looks like hay, throwing it everywhere while searching for blueberries, peas, carrots and peanuts that Maria Schwalbe, her primary keeper, hides in the wool.

Something old, something new

The zoo is the oldest in the United States, and just last month opened the Great Ape Trail. It’s part of a trail network throughout the zoo that, when finished, will allow many animals to travel, explore their environment and interact more with visitors. It’s the first of its kind in the world.

The ape trail extends over a visitor path and through the tops of trees, from 11 to 16 feet off the ground. It is next to a lake and allows Batu and her mother, Tua, to explore the world outside their habitat. Think of it as giving them a chance to see more of their neighborhood while giving visitors a chance to see them where they most like to be: up high, as if in trees.

The zoo is home to three Sumatran orangutans, which zoo president Vikram Dewan describes as “the great ape closest to extinction.” Only about 6,000 of the orangutans live in the wild, all in Indonesia.

Orangutans are primates, which are mammals. Like humans, they have fingers, fingernails, eyes that face front, opposable thumbs to grab things and large brains. They usually have reddish-brown shaggy hair and can live more than 50 years.

Mongoose lemurs run on a protected path above a walkway at Philadelphia Zoo. (Matt Rourke/AP)

Batu and Tua enter the trail from their yard. They go through a metal door that must be opened by a zookeeper. Next, they climb stairs up a tower to the trail, which looks like large rooms that link to each other. The rooms. including most of the floors, are enclosed in flexible steel mesh (like a screen door).

More trails to come

The new trail system will cover about 1½ miles over all 42 acres of the zoo in 10 years, Dewan says. Many of the 1,300 animals — including rhinos, bears and giraffes — will be allowed to roam.

While visitors watch and learn about Batu and Tua, primate expert Meredith Bastian and the zookeepers watch and learn more about orangutans. They want to see how the orangutans will be affected by their larger environment and what they learn. “Great apes are smart,” says Bastian, who grew up in Falls Church and spent a lot of time as a child looking at apes at the National Zoo and the Smithsonian’s Museum of Natural History.

— Sue Kovach Shuman