Animals are sometimes housed in zoos for beneficial reasons such as educational purposes, providing habitat for animals unable to survive in the wild, and research purposes. A significant amount of research is conducted on factors that might be stressful to wildlife to improve the welfare and well-being of captive animals; however, an equal amount of research is not being performed on each stress factor that could affect captive wildlife.
Despite zoo animals being put on display and constantly exposed to human presence, the effect of human presence and crowd sizes on captive animals has not been extensively researched. For apes, some studies have been conducted with gorillas (Gorilla gorilla) and even fewer with chimpanzees (Pan troglodytes); the methods and results of the studies are inconsistent and therefore do not provide an accurate representation of the effects crowds have on each species nor the effects on one species compared to the effects on another.
Studies conducted by researchers like Carder and Semple or Stoinski look at the impact of crowd sizes on gorilla behavior, but the results of the two studies contradict each other (Carder & Semple, 2008) and (Stoinski, Jaicks, & Drayton, 2012). This is true with many studies that have been previously conducted, so there is no commonly accepted or consistent knowledge about the effects of human presence on zoo-housed apes.
In the article chosen, Bonnie, Ang, and Ross focus on the ecology of zoo-housed apes and observe the effect of human presence on ape behavior as well as the effect on the relationship of apes to their environment. With the experiment, Bonnie, Ang, and Ross hypothesized a correlation between human presence and the behavior and exhibit use of apes. The researchers hypothesized that the presence of humans would negatively affect the apes and the presence of large crowds would lead to an increase in abnormal behavior as well as behavior induced by anxiety.
The researchers also hypothesized the presence of humans would lead to an avoidance of the exhibit closest to zoo visitors and less frequent use of this portion of the exhibit (Bonnie, Ang, & Ross, 2016). To test their hypotheses, the researchers conducted an experiment using observations from 2 social groups of apes in the Lincoln Park Zoo in Chicago, IL. The social group of the gorilla consisted of 1 adult male, 1 adolescent male, and 3 adult females; the chimpanzee social group consisted of 2 adult males and 4 adult females.
The exhibits of the apes were nearly identical: 4 exhibits, out of which 3 were viewable by the public, an indoor playroom, an outdoor yard, and an off-exhibit holding area. Exhibits were separated from the public by a glass partition that spanned the entire length of the indoor exhibits. The indoor exhibit and outdoor yard were separated by sliding glass doors. The apes were enclosed in the outdoor yard using mesh wiring, with several meters separating the mesh wiring from the visitor walkways.
The enrichment provided in these exhibits included nesting material, toys, mirrors, puzzle feeders, and food all distributed throughout the exhibits to encourage the apes to explore different parts of their exhibits. For 22 hours a day, the apes were housed in the indoor and outdoor exhibits viewable by the public. For the other 2 hours in the day, the apes were moved to off-exhibit holding areas so that the exhibits could be cleaned. Access to the outdoor yard as well as the size of the crowd at the time of observation were noted when data was collected.
Zoo visitor crowd sizes were categorized into 3 groups: staff-only crowds, small crowds which consisted of 1-30 zoo visitors, and large crowds consisting of 30+ zoo visitors (Bonnie, Ang, and Ross, 2016). The data subset included examined behavioral data collected during the weekdays from 10:00 am to 5:00 pm when the zoo was open to the public. Data was collected by individuals who received extensive training and demonstrated observer reliability by having a high percentage of sample agreement with an experienced researcher.
The observations consisted of the apes’ behavior with varying crowd sizes present and their spatial use within the exhibit. When observing spatial use, a 30-min group scan was conducted with 1 minute intervals between samplings. During the group scans, the position of the ape in the exhibit was recorded on digitalized map of the exhibit using a hand-held tablet. The proximity to visitor zone (PVZ), the area of the exhibit closest to zoo visitors, for each exhibit was defined as 1 meter between the glass partition and exhibit as well as within 2 meters of the ground floor.
The behavior of individual subjects was collected in 10 minute sessions with a 30 second interval between sessions. Behavioral data was recorded on a table that consisted of 13 behavioral categories, with a total of 73 behavioral samples collected. Once all the data was collected, the data to be examined was selected. The data analyzed was data collected within 12 consecutive months with unchanging social groups and no births occurring. The data selected only consisted of time periods where the social groups were housed in a single exhibit, not moved from one exhibit to another.
If a subject was out of view of the public for more than 33% of the samples for a period of data collection, the data was excluded. Based on these restrictions, the data used for chimpanzees was collected between August 1, 2012 through July 31, 2013 and for gorillas was collected from August 1, 2010 through July 31, 2011 (Bonnie, Ang, and Ross, 2016). The results obtained from the experiment were not what were expected. In regards to behavior, access to the outdoor yard and the size of the visitor crowd had no effect on grooming or object-related behaviors in chimpanzees.
The only significant effect of crowd size on behavior was found with self-directed behaviors in both gorillas and chimpanzees. In both social groups, the frequency of self-directed behaviors with staff-only and small crowd sizes present were decreased when outdoor access was granted. On the other hand, the presence of large crowd sizes led more frequent self-directed behavior when outdoor access was granted than when both social groups only had indoor access. For the gorilla social group, the use of the PVZ was not affected by crowd sizes nor by whether they had access to their outdoor yard.
The use of PVZ by the chimpanzee social group was also not affected by crowd size, however, access to the outdoor yard led to a decrease in PVZ use. (Bonnie, Ang, and Ross, 2016). Contrary to the hypothesis, the experiment concluded that large crowd sizes did not lead to more frequent displays of abnormal behaviors compared to other crowd sizes; there was no significant difference in behavior frequencies exhibited between the various crowd sizes present (Bonnie, Ang, and Ross, 2016).
Overall, the experiment concluded that crowd presence had little effect on the spatial use of both gorillas and chimpanzees, specifically the use of the PVZ. It appears being granted or denied access to the outdoor yard played a more important role in crowd effects on apes and is a factor that should be researched. In general, gorillas and chimpanzees exhibited more similar than different responses to various crowd sizes as hypothesized by the researchers.
The conclusions of Bonnie, Ang, and Ross were justified based on the methods used and data collected. The experiment was designed to appropriately test the hypotheses and data analyzed showed the significance of the results obtained. The experiment attempted to eliminate inconsistencies between the species groups to make a better comparison between the responses of the two species and provide more information about how the welfare of zoo-housed animals can be improved upon in regards to human presence.
The biggest limitation of the study was the number of subjects used; the small number of subjects in the study limited the results and data obtained. Because there were only two social groups of apes, one group of gorillas and one group of chimpanzees, in one zoo, the results are not a good representation of the overall impact of humans on apes. To provide more accurate results, the less social behavior of gorillas compared to chimpanzees should be taken into account because it could affect the reactions and explain possible differences in gorilla and chimpanzee reactions.
Another factor to consider is that some animals prefer some areas and avoid others regardless of the size of the crowd which could explain differences in PVZ use. I am interested in working with wildlife and have an interest in animal behavior, so the study conducted by Bonnie, Ang, and Ross provides some insight into how my working with or near wildlife might affect the way the animals will behave. The impact of human presence on captive apes is complex and influenced by many variable and therefore requires more observation and testing to provide more extensive and consistent results.
