As the Smithsonian’s National Zoo’s great apes prepare to go to sleep, they make their beds, then settle in. Just like their wild counterparts, orangutans in zoos build cozy nests. Where an orangutan chooses to snooze at night can give keepers insight into their social preferences, according to a study entitled “Nest location preferences in zoo-housed orangutans,” published in Applied Animal Behaviour Science. Get the scoop on the study from Primates Curator Meredith Bastian.
Why do orangutans build nests?
Orangutans build nests primarily for the same reason that humans use beds—to have a comfortable place to sleep. Wild orangutans will either build a new nest or re-enter an old nest every night. They will also often rest in nests during the day. If Zoo visitors watch our orangutans for long enough, they are sure to see some interesting nests!
A fun fact about orangutan nests—and night nests, especially—is that where an orangutan builds a nest can indicate whom they prefer to socialize with, thereby giving the primate staff some insight into the orangutans’ relationships with one another.
One of our adult female orangutans, Batang, and her male infant, Redd, split their time between three groups: Kyle and Bonnie; Kiko and Iris; and Lucy. Batang and Redd also have the option to spend time together by themselves overnight. Other days, Batang—with Redd in tow—readily chooses to spend the night with the other adult orangutans.
How did the idea for this study come about?
My Ph.D. dissertation documented cultural behavior in wild Bornean orangutans at two field sites in Indonesian Borneo. Some of the most interesting differences I documented between wild orangutan populations was their nesting behavior. This prompted me to learn more about nesting behavior in zoo-housed orangutans and team up with others who shared my interest in great ape nesting behavior.
This study focused on the Smithsonian’s National Zoo’s orangutans but also included a survey of other zoos accredited by the Association of Zoos and Aquariums that house orangutans.
What do the Zoo’s orangutans use to build nests?
Keepers provide our orangutans with a variety of materials to create nests, including hay, leafy browse, cardboard, sheets, blankets, fleece and many other materials. They often incorporate enrichment items—such as milk crates—into their nests as well.
Are there differences in how individual orangutans build nests?
Yes. Although all wild orangutans use leaves to embellish their nests with leafy pillows, blankets or mattresses, the frequency with which each type of embellishment is used varies across populations and sites.
Differences can also stem from individual preference. For example, Batang makes very elaborate nests. A few days before she gave birth to Redd, she created an even larger and more elaborate nest! Since she has given birth, we have not formally documented her nesting behaviors or location preferences. However, the primate team has noticed that she has made larger and more well-cushioned nests since Redd’s arrival.
Redd has been observed making his own “practice” nest, but he always shares a night nest with Batang. He will continue to do so for many more years.
How do orangutan nests in the wild differ from zoo nests?
Nesting materials in the wild are leafy tree branches, whereas in zoos we give orangutans a variety of potential nesting materials, nearly all of which are incorporated into nests.
The location of nests differs, too. Wild orangutans nearly always nest in the treetops, whereas orangutans housed in zoos tend to nest in close proximity to the ground or on the ground. This is not surprising in part because zoo-housed orangutans do not face the same pressure from predators that wild orangutans do.
Our orangutans can choose whether they want to nest up on a platform, in a hammock or other elevated areas within the exhibit. We give them as many opportunities as possible to nest off the ground. Having multiple nesting areas also allows individuals to nest closer to those they have a close social relationship with and farther away from those with whom they may not have as close a bond.
Do orangutans share nests?
Night nest sharing by adult orangutans is rare for both wild and zoo-housed orangutans. All known instances of nest sharing have been individuals who are very closely bonded. Sharing nests during the day, however, is much more common. Keepers have observed an adult male-female pair as well as a pair of females sharing a nest.
Why might an orangutan change nests overnight?
Our primate keepers look for behavioral cues—including the proximity of orangutans to one another, as well as the amount of time they choose to spend together—to determine orangutans’ social groups.
Two orangutans that may begin the night in one nest may relocate to a different nest when keepers arrive in the morning. This change in nesting locations is likely the result of social interactions that took place overnight.
Orangutans rarely nest in close proximity to one another of there are any social tensions between individuals, no matter how small. Alternatively, an orangutan may change his or her nest location in order to be closer to another individual.
What did you hope to learn by studying nesting patterns?
Before this study began, we thought that using night nest proximity would serve as a way for us to decipher relationships between our orangutans. We were pleasantly surprised that it is indeed a good alternative to the traditional method of tracking whom their nearest “neighbors” are during daytime activities.
This story appears in the September 2018 issue of National Zoo News. During your next Zoo visit, don’t miss the daily 1:30 p.m. research demonstration at Think Tank and other amazing animal encounters! Co-authors on this paper are David R. Glendinning, Alexandra J. Reddy, Elizabeth S. Herrelko, Melba Brown, Elizabeth Renner and Laurie Thompson.