Smithsonian National Zoological Park l Friends of the National Zoo



The O Line

It's a thrilling sight to see the orangutans traveling on the Zoo's Orangutan Transit System, or O Line. The O Line gives the orangs freedom of movement, an expanded living area, and choice of location.

Orangutans are brachiators, which means they can swing hand over hand from branch to branch. Kiko, an adult male, often demonstrates this form of locomotion on the O Line. The other orangutans, however, usually walk or shuffle along the cables, holding on with two or more limbs.

link iconFrequently Asked O Line Questions

When Think Tank curators were deciding which animals to include in the exhibit, they wanted to include orangutans but were faced with a number of challenges. The exhibit space at Think Tank was not big enough to permanently house a large number of orangutans. Because of the building's status as a historic landmark, major renovation to expand the exhibit space was not an option. Additionally, the orangutans' permanent home, the Great Ape House, is some 490 feet (149.5 m) from the new exhibit.

The solution? Let the animals move themselves! Curators designed the world's first Orangutan Transit System (OTS), a system of towers and cables that allows the animals to move between the two buildings.

The Orangutan Transit System, or O Line, consists of eight 50-foot-high (16.6 m) towers connected by plastic-coated, steel cables. At the lowest point, the cables are about 40 feet (13.3 m) off the ground. The entire distance of the O Line is about 490 feet (149.5 m). Tower 1 is in the outdoor orangutan yard at the Great Ape House. Tower 8 is in the outdoor orangutan yard at Think Tank. The towers in between are outside the confines of the animal yards, and the O Line crosses Olmsted Walk twice. Patterned paver sections on Olmsted Walk alert visitors to the orangutans crossing overhead. A third crossing is highlighted in front of Think Tank.

The O Line is open to any orangutan given access to the yards at Think Tank or at the Great Ape House. The towers in the yards (1 and 8) are fully open for climbing. Towers 2 through 7 have only the top platform open to the orangutans. There are wide wire "skirts" below these platforms to keep the orangutans from climbing down.

The skirts and surrounding grid "collars" are electrically charged to keep the orangutans from climbing down (and visitors from climbing up) the towers. The charge in the system is just enough to give an orangutan a sharp sting without causing injury. Each tower is connected to an alarm system that the Animal Care staff can see and hear to alert them of any problems with the line. The electric supply to the towers is connected to an emergency generator, which triggers the alarm when called into use.

A keeper monitors the orangutans whenever they have access to the towers (usually between 11 a.m. and 2 p.m.). The orangutans are given access to the O Line when the temperature is above 40 degrees Fahrenheit without strong winds or precipitation.

Since orangutans are brachiators and can swing hand over hand from branch to branch, some orangutans use this method to cross the O Line. However, most of them walk or shuffle along the cables, holding on with two or more limbs. In the wild, this movement distributes the animal's weight among several branches.

Whenever the orangutans have access outside, they have access to the O Line. It is their choice whether or not to travel the O Line, and one orangutan, Lucy, has yet to choose to travel. Some orangutans travel on the O Line as soon as they go outside, immediately traveling to the opposite building. Others choose to take their time and travel slowly, preferring to sit atop the towers and watch the visitors below. In the afternoon, the orangutans are allowed the choice of which building to spend the night in, Think Tank or the Great Ape House. The O Line allows our orangutans flexibility and choice in their lives.