The Drill Enrichment and Behavioral Study
Problems:
1. Is there a significant difference between the
mean activity time for the male drill on days with enrichment and days
without enrichment?
2. Is there a significant difference between the mean activity time for
the three female drills on days with enrichment and days without enrichment?
Subjects
(One male and three female drills at the Columbus Zoo)
Lyle
Eschu
Nora
Bioko
Hypotheses:
1. There is a significant difference in the mean
activity time for the male drill when enrichment is present and when enrichment
is not present
2. There is a significant difference in the mean activity time for the
three female drills when enrichment is present and when enrichment is
not present.
Statistical Test:
The statistical test used is a a two-tailed z-test, of independent sample means, and a two-tailed f test, of independent sample variances. The study was conducted using an a = 0.05 and was completed in 76 days of observations. The confidence level for the study was 95%.
Abstract:
This study was conducted on the Drills (Mandrillus Leucophaeus)
in the African Region of the Columbus Zoo and Aquarium. Every Monday and
Wednesday the drills were provided enrichment. It was questioned if enrichment
had an effect on the amount of time the drills were active in a two-hour
period. Data were collected four days a week on the amount of time the
drills were active and the amount of time they spent with the enrichment.
The results of this study were found to be inconclusive stating that there
was not enough evidence to support the claim that enrichment had a significant
effect on the amount of time the drills were active during a two-hour
period.
Movies:
Results:
The purpose of this study was to determine if enrichment had a significant effect on the amount of time the drills are active during a two-hour period. The first hypothesis stated there was a significant difference in the mean activity time for the male drill when enrichment was present and when enrichment was not present. The second hypothesis stated that there was a significant difference in the mean activity time for the three female drills when enrichment was present and when enrichment was not present.
Hypothesis 1 Results:
The following includes the results for the first hypothesis conducted on the male drill, Lyle. Sample (1) included data reflecting the male drills minutes of activity during two-hour periods when enrichment was provided in the exhibit. Sample (2) included data reflecting the male drills minutes of activity during two-hour periods when enrichment was not provided in the exhibit. The data were analyzed using a two-tailed, z-test of independent sample means at a 95% confidence level to determine if there was a significant difference in the means of the two samples. The variance values were calculated and an f test was used to determine if there was a significant difference in the dispersion between the two samples. A confidence interval was calculated for both the means and variances at an a=0.05. Table 1 provides the results of the data analysis.
Table 1: Hypothesis 1 Results (means, variances, & confidence interval)
| Statistic | Sample (1) | Sample (2) | Results |
| n | 33 Days | 43 Days | |
| Mean | 33.424 Minutes | 22.698 Minutes | |
| Standard Deviation | 28.899 | 21.603 | |
| Critical z | 1.96 | ||
| z statistic | 1.784 | Fail to Reject Null | |
| Confidence Interval for Means | (23.564 minutes, 43.284 minutes) | (16.241 minutes, 29.155 minutes) | |
| Variance | 835.127 | 466.692 | |
| df | 32 | 42 | |
| Critical f | 1.94 | ||
| f statistic | 1.79 | Fail to Reject Null | |
| Confidence Interval for Variances | (568.851, 1591.571) | (330.307, 802.237) |
Figure 1: Comparison of Sample Means for the Male Drill
Figure 1 shows the difference between the means for the male drill on enrichment days compared to non-enrichment days.
Summary
The results of the z test for the first hypothesis were found to be
inconclusive. There was non enough evidence to support the claim, which
stated that there was a difference in the mean activity time for the
male drill when enrichment was present and enrichment was not present.
Hypothesis 2 Results:
The following includes the results for the second hypothesis conducted on the three female drills: Nora, Bioko, and Eschu. Sample (1) included data reflecting the average number of minutes, during a two-hour observation period, the three female drills were active when enrichment was provided in the exhibit. Sample (2) included data reflecting the average number of minutes, during a two-hour observation period, the three female drills were active when enrichment was not provided in the exhibit. The data were analyzed using a two-tailed, z-test of independent sample means at a 95% confidence level to determine if there was a significant difference in the two means of the samples. The variance values were calculated and an f test was used to determine if there was a significant difference in the dispersion between the two samples. A confidence interval was calculated for both the means and variances at an a=0.05. Table 2 provides the results of the data analysis.
Table 2: Hypothesis 2 Results (means, variances, & confidence interval)
| Statistic | Sample (1) | Sample (2) | Results |
| n | 33 Days | 43 Days | |
| Mean | 52.157 Minutes | 46.488 Minutes | |
| Standard Deviation | 28.9 | 29.377 | |
| Critical z | 1.96 | ||
| z statistic | 0.841 | Fail to Reject Null | |
| Confidence Interval for Means | (42.297 minutes, 62.018 minutes) | (37.707 minutes, 55.269 minutes) | |
| Variance | 835.226 | 863.012 | |
| df | 32 | 42 | |
| Critical f | 2.01 | ||
| f statistic | 1.03 | Fail to Reject Null | |
| Confidence Interval for Variances | (568.919, 1591.759) | (610.807, 1483.506) |
Figure 2: Comparison of Sample Means for the Female Drills
Figure 2 displays the difference between the means for the female drills on enrichment days compared to non-enrichment days.
Summary
The results of the z test for the second hypothesis were found to be
inconclusive. There was non enough evidence to support the claim, which
stated that there was a difference in the mean activity time for the
three female drills when enrichment was present and enrichment was not
present.
Conclusion:
The purpose of this study was to determine if the enrichment provided by the keepers would affect the amount of time the drills were active. The first hypothesis tested in this study stated that enrichment would affect the amount of time the male drill was active during a two-hour period. The second hypothesis tested in this study stated that enrichment would affect the amount of time the three female drills were active during a two-hour period. The results of this study were found to be inconclusive. Therefore, there was not enough evidence to say that enrichment had an effect on the amount of time the drills were active during a two-hour period.
Implications:
The results concluded from this study show that there was not enough evidence to reject the null hypotheses. The first null hypothesis stated that there was no difference in the mean activity time for the male drill when enrichment was present and when enrichment was not present. The second null hypothesis stated that there is no difference in the mean activity time for the female drills when enrichment was present and when enrichment was not present. These hypotheses may be rejected with additional research or data. However; for the purpose of this study, there was not enough information to state that the hypotheses are false. With this information, implications can be drawn from this study. Providing an alternative form of enrichment to the drills may boost the amount of activity displayed. According to the data collected, the drills responded poorly to the boomer ball and spools provided to them. The drills had a higher rating when natural enrichment was provided to them, such as elephant grass and wild birdseed. To increase the amount of activity the drills display, natural enrichment should be provided more often and boomer balls and spools should be used less.
Factors Affecting the Results:
The drill’s exhibit is set up into three sections. The larger outside section, the inside display section, and the inside off display section. When taking observations, the keepers would occasionally allow the drills access to all parts of the exhibit. The observer was forced to choose which portion would provide the best data. However; the drills residing in the other portion where out of sight to the observer. Therefore, data for the particular drill, or drills, was inaccessible at the time. The activity the drills performed while out of sight to the observer was not included in the data collection, thus possibly slightly altering the outcome of the results.
Columbus Zoo & Aquarium School: 2006
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