Ci Wen Yang and Chien-Jen Yang

This paper describes the foraging environmental enrichment programs designed to stimulate natural behavior of gorillas, chimpanzees and fat-tailed lemurs in Taipei Zoo. These experiments have resulted in the extension of their feeding time and increase their social interaction.

Environment enrichment is an important and adopted zoo management tool for the captive primates in modern zoos. In order to promote animal conservation education, we invited Dr Hunthius, the conservation and science director of the American Zoo Association, with his group of animal behavior researchers to conduct a workshop ‘The application of behavior study in animal management’ in 1992. A series of programs were initiated to enrich the animal behavior. With the operation of some key elements within the captive environment, including foraging and management design, the natural behavior of the animals was stimulated to reduce the occurrence of abnormal behavior. This report is the study results of primates.

A two-year-old gorilla named ‘Pao-pao’ arrived at Taipei in 1987, and a 23-year-old silverback gorilla named ‘Hei-pei’ was donated to the zoo in July 1993. We fixed a 60-cm long by 12-cm diameter feeder made of heavy plastic pipe to the entrance to the two gorillas’ cage in early March 1996. To help the animal understand the purpose of the feeder a 3-cm wide cleavage was made along its side, allowing the animals to scoop out food. ‘Pao-pao’ spent twice as long feeding as usual. The following day, the feeder was modified; finger holes were made along its length, and two exit holes at the ends in which two fingers could be inserted to extract food. Previous experience with feeders had taught ‘Pao-pao’ that food was obtainable from within, and as we had anticipated he was able to manipulate the food toward the exit holes. Later, he was observed striking the upper part of the pipe to knock the food down into the lower plastic pipe, in order to get food more quickly.

Shortly after, we introduced a similar apparatus on the platform inside the gorillas’ exhibit. Being higher in rank, ‘Hei-pei’ was given the first try at extracting food. Initially, his lack of previous experience prevented him from succeeding in this; however, after sniffing it several times and licking the exit holes, he eventually worked out how it worked and was able to scoop food out with his fingers.

At Taipei Zoo, there are twenty-two chimpanzees; thirteen of them were bred in the Taipei Zoo. In the beginning of 1993, a food tray containing fruit juice and honey was put in the side of the tree to allow access. By poking a bamboo twig through the hole juice and honey could be extracted. The chimpanzees greatly enjoyed this activity which combined food gathering and play.

In a second tree, monkey rice and raisins were placed in holes in its side and the chimpanzees used their fingers to get them. These methods encouraged social activity and increased the time spent foraging.

Small-bodied and only 15 cm long, the agile Fat-tailed Dwarf Lemurs (34) are displayed behind glass in the Nocturnal Animals House; they are easily seen only at feeding time. Their food is placed in a bamboo tube with a diameter of 5cm and a depth of 2.5~3 cm suspended near the platform in the center of the cage (2.8m x 2.5m x 1.6~3m), replacing the old method of feeding from a bowl placed on a raised surface. The lemurs have to work their way down a rope to get at the food; they also jump up to strike the container, immediately leaping onto the facing ledge to pick up food that has been dislodged.

According to Wranghm’s study in 1997, there were 141 species of trees and other plants eaten by chimpanzees. About 25% to 45 % of the chimpanzee diet are leaves and blossoms. In the wild, chimpanzees spend 35% to 68% of their time feeding (Goodall, 1986). In captivity, chimpanzees spend far less time feeding and foraging, as the variety and of foods are limited.

At Taipei zoo, thirteen kinds of plant foods are included in the daily diet of chimpanzees and twelve kinds in that of the white-handed gibbon (Table 1, Table 3). In these experiments, six chimpanzees and two gibbons were observed to find the effects of time spent feeding when mulberry branches and leaves were added to their diet.

Table 1. Daily diets for each chimpanzee in a separate enclosure (a group of six animals), the weight of food, % and total amount.

Table 2. Nutrient content in the diet of the chimpanzee.

On 23rd August 97, a group of chimpanzees (one male and five females) were observed for their feeding behavior. They had been given the regular diet without any addition of mulberry. The observations were recorded every minute for the time period from 9:30 to 11:30 and from 15:30 to 17:30.

Then, on 25th and 26th August, mulberry branches and leaves were added to their diet and their feeding behavior observed and recorded over the same time periods as on 23rd August. In the morning, monkey cake and monkey rice was given to the chimpanzees and during the afternoon they were fed on fruits, vegetable and bread.

The results show the percentage of feeding time increased from 10 % to 47.5 % in the morning and from 20 % to 56.7 % in the afternoon after adding mulberry branches and leaves to their diet. The next day we searched for what remained of the branches and found only small chips of 1-5cm in length left.

Two white-handed gibbons that live separately in two enclosures were observed for their feeding behavior. The same methods as above were applied to these two gibbons. In the morning, monkey rice and cake was given to the animals and they were fed on fruits, vegetable and bread in the afternoon.

Table 2. Daily diet for each white handed gibbon in a separate enclosure, the weight of food, % and total amount.

Table 4. Nutrient content in the diet of the white handed gibbon before and adding mulberry branches and leaves.

After adding mulberry leaves in the diet, the percentage of feeding time increased from 13.6 % to 16 %. There was no large difference when adding mulberry leaves to the diet, perhaps due to their solitary condition in temporary habitats.

Zoo animals have little chance to experience the activities of foraging and social interaction. The primates, especially apes and monkeys are very intelligent and need to receive a great deal of activity oriented stimulation to make their lives interesting. This also benefits the zoo visitor who will experience and enjoy natural animal behavior. Environmental enrichment will certainly decrease abnormal behavior as well, such as body weaving, stereotyped pacing, regurgitation, re-ingestion of food and coprophagy as a compensation for the environmental fluctuation of the animal world due to the boredom of zoo life (Yang, C.J 1997). The application of environmental enrichment for captive animals aims at providing activities for animals to occupy their time and to stimulate their thinking. Primates in the wild spent almost half the day in foraging for food. In contrast, animals in captivity are fed regularly once or twice a day. Providing the suitable feeding strategies, such as scattering food on various substrates; hiding food in logs, rocks and toys; providing browse material, and providing live prey, such as worms, crickets and fish, can extend time spent feeding.

The foraging environment enrichment for the gorillas, chimpanzee and fat-tailed dwarf lemurs has resulted in the extension of their feeding time. The chimpanzee and fat-tailed dwarf lemurs showed less stress, and were more active. Both animals have bred successfully. In experiment 1, after adding mulberry branches and leaves to the chimpanzees’ diet, the time spent feeding increased dramatically. But in experiment 2, there was no big difference. The reason may possibly be due to the gibbons feeding alone.

The wild is almost unpredictable, but the environment of the zoo is just a cosmetic imitation of nature’s landscape. When animals, especially the primates, live in an unchangeable environment for some time, they will be bored. The strategy of environmental enrichment is to enrich the living environment of captive animals, it should be applied according to the natural behavior of the animals. Regular supply of food hunt or change of furniture is effective ways for environmental enrichment. However, such acts will increase the working time of keepers, so animals’ houses and feeding should be planned accordingly to facilitate the operation. In short an exhibit should never be regarded as finished.

Following Taipei Zoo’s move to a new site in 1986, most of the personnel and financial resources were invested in an effort to turn itself into a fully modern zoo. In the last few years within the constraints of limited resources, the zoo has undertaken several programs onenvironmental enrichment for captive animals. Though there are many unknowns for us to overcome when promoting environmental enrichment, it is certainly the right way to approach modern zoo management.

I am particularly grateful to our duty director Mr. Chang Poe-Chung who encouraged me to do this research. Thanks to Miss Cho, Lin-Lin and Mr. Liou, Chin-Der for their hard work over this summer. And thanks to all my friends at Taipei Zoo, without their help this work would have been impossible.

Cho, Lin-Lin and Yang Ci Wen 1997 The diet of primates in Taipei Zoo. Student summer practice report on August 1997.

Goodall, Jane 1986 The Chimpanzees of Gombe, USA. : Harvard university.

Liou, Chin-Der and Yang Ci Wen 1997 The chimpanzees at Taipei Zoo. Student summer practice report on August 1997.

Peterson, Dale and Goodall, Jane 1993 Vision of Calibrate: on chimpanzee and People.

Yang, Chen-Jun. 1996 The Environmental Enrich at The Taipei Zoo. Taipei Zoo Bulletin Volume 9:67-77 June 1997.