By:  Les Stegenga, Keeper, Calgary Zoo,
Alberta, Canada

Most zoos today recognize the importance of providing a social structure and physical setting comparable to the features found in nature.  The sterile, concrete cages are on their way out.  Taking their place are more naturalistic exhibits.  However a captive environment also requires continuous opportunities for stimulation, without which animals become accustomed to the repetition of events and the similarity of the exhibit.  As an example, spider monkeys (Ateles geofferyi) in the wild will spend much of their time in food gatherings activities, often traveling widely over their home ranges during seasonal food fluctuations.  In captivity, these daily demands are greatly reduced.  By introducing naturalistic variables to a display, spider monkey behaviors can be challenged and moderated to provide more alert, active and diverse behaviors.  A study of spider monkeys in a naturalistic exhibit at the Calgary Zoo found that the addition of leaves and food pods reduced off-display time and increased feeding activity.

The main spider troop at the Calgary Zoo consists of 25 individuals, 1.4 breeding adults and 1.1 juveniles.  They are housed in an indoor exhibit that has incorporated many naturalistic features., including sculptured floors, trees., intertwined ropes and nets, and non-fixed materials like tree branches.  However, from random observations by keeper staff and occasional comments from the viewing public, it appeared that the spider monkeys were spending a significant amount of time in a smaller more sterile off-display holding area.

Before any enrichment additions were made to the on-exhibit enclosure, baseline data on the spider monkeys' behavioral patterns was collected.  A total of 584 minutes of behavioral observations were recorded during a sixteen day period.   Two enrichment experiments were then conducted.  The first consisted of adding a partial floor covering of leaf litter collected from the Calgary Zoo fall leaf recycling program.  The contents of one large garbage bag were stacked into two piles in the front corners of the main exhibit.  When food was distributed during the morning and evening feedings, it was scattered throughout the exhibit as well as into the leaves.

The second experiment consisted of adding a food pod that had been initially designed for apes.  The food pod made of sturdy, three-inch-diameter PVC pipe, approximately one yard in length.  Removable ends allowed contents, ranging from a mixture of puffed wheat, sunflower seeds., and peanuts to frozen flavored juices, to be placed inside.  Extraction of the contents could only occur from the three 3/4-inch-diameter holes drilled into the sides of the pod.  The pod was then suspended from one of the trees.  Food was added to the pod only once per day, although this occurred at any point in time throughout the day.  The baseline data that had been collected indicated that the spider monkeys were off display 30.2 percent of the time.  The introduction of the new environmental variables, the leaves and the food pod, reduced the amount of off-display time by nearly half.  Feeding and foraging time also increased significantly.  During baseline observations, the monkeys spent 7.3 percent of their time feeding, but when leaves were added to the enclosure, feeding activities increased to 13.1 percent of the time.

The spider monkeys spent considerable effort in searching for food through leaves even when it appeared that all food was consumed.  The monkeys also spent 9.5 percent of their time attempting to extract food from the pods.  When the leaves were added to the enclosure, playtime was more significant---19.6 as opposed to the baseline 11.5 percent.  Both juveniles spent considerable time playing in the leaves., and this activity often spilled over to the adults, who responded to the increased levels of activity.  The two experiments clearly showed that the introduction of new variables results in positive behavioral consequences.  Both leaves and food pods could be further increased if two were placed in the enclosure.  This would reduce the possibility of any antagonistic behavior.  Food pods could also be filled more than once per day, although consideration must be given to the possibility of overfeeding.   The addition of leaves could be done on alternate works to increase variability.   Similar floor covering materials, such as straw, wood wool, or hay, could also be used.