<em>By Margaret Bryer and Shelby Schwartz, Great Ape House Interns
Smithsonian National Zoological Park, Washington, DC</em>

<strong>Abstract</strong>
The Smithsonian’s National Zoological Park’s orangutan transit system, known as the O Line, is an excellent form of enrichment for the zoo’s orangutans, giving them the opportunity to practice their natural locomotor ability. The O Line is also beneficial because it provides the orangutans with behavioral choices beyond the limitations of their outdoor yard. To better understand this unique exhibit’s value to the animals, we collected data on behavior and use of the O Line. We observed the variety of ways the orangutans move along the Line. All five individuals who choose to travel the O Line locomote in several different ways above, below or along the plastic-coated steel cables connecting the Line’s towers, though only one individual brachiates. The different components of the O Line -- the eight 50-foot towers, the cables connecting them, and the fire hoses connecting the towers to the yards -- are not merely a form of transportation, but forms of enrichment independently as well. We therefore examined how frequently orangutans used the hoses in play or in other behaviors instead of as a means to climb the tower, as well as how frequently they rested in the towers and on the cables. The behavioral freedom introduced with the O Line also includes the option to spend the night in the indoor enclosure at Think Tank, so we also kept track of how often the animals remain at Think Tank versus how frequently they return to the Great Ape House for the night. Finally, we studied how several of these factors are affected by temperature and crowd size. Together these behavioral data illustrate the enrichment impact of this innovative exhibit, as it dramatically expands the behavioral choices available to an intelligent and primarily arboreal great ape often confined to limited indoor and outdoor enclosures in captivity.

<strong>Introduction</strong>
This National Zoo’s unique O Line exhibit is an orangutan transit system opened in 1995 consisting of eight 50-foot towers connected by plastic-coated steel cables spanning a total distance of 490 feet. The O Line allows the orangutans to commute between the Great Ape House and Think Tank (an exhibit on animal thinking). The O Line traverses two visitor walkways, providing a proximity to visitors that no other zoo in the United States offers.

Many agree that giving animals control over their environment increases their psychological well-being (Novak and Drewsen, 1989; Rumbaugh, Washburn and Savage-Rumbaugh, 1989), and the O-Line provides a dramatic expansion of the orangutans’ behavioral and spatial choices. The National Zoo’s orangutans are able to choose where to go and how to move along the 490-foot system, and ultimately which building to occupy.  This arrangement also allows individuals a certain amount of control over their companions, a choice often eliminated in small zoo enclosures.

The O Line is also a wonderful educational opportunity. Zoo visitors can watch these naturally arboreal animals move above them with ease, an opportunity lost in traditional enclosures in which orangutans are primarily confined to the ground. The awe-inspiring sight of an adult male orangutan brachiating or a young orangutan resting on the Line and looking down at visitors is a great way for visitors to better understand this species and increase interest in great apes.

<img class="alignnone size-large wp-image-1026" title="o_line_crowd_picture" src="http://aecetia.net/gws/aazk/wp-content/uploads/o_line_crowd_picture-768x1024.jpg" alt="o_line_crowd_picture" width="768" height="1024" />

<em>NZP visitors look skyward to observe the zoo’s orangutans negotiating the O Line between the Great Ape House and the Think Tank.</em>

Five of the six resident orangutans choose to use the O Line when they are given access, weather permitting, from approximately 1030 – 1400 hrs daily. Towers 1 and 8, in the two yards, are open for the orangutans to climb. Towers 2 through 7 have electrified wire “skirts” below their platforms that………

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