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CZAAWE Resource Article
Black rhinoceros (Diceros bicornis) in U.S. zoos: II. behavior, breeding success, and mortality in relation to housing facilities
Year of publication
John Wiley & Sons, Inc.
Abstract The captive population of black rhinoceros (Diceros bicornis) is not self-sustaining. The reasons for suboptimal reproduction and high mortality need to be investigated. This can only be achieved by cross-institutional analyses of environments, behavior, and performance. In this study, we collected data on 23 zoos with black rhinoceros to compare zoo environments with reproductive success, mortality, and behavior. Institutional variation was characterized by enclosure area, percentage of walls around enclosure perimeter, percentage of public access along enclosure perimeter, climate, noise level, number of years zoo has maintained black rhinoceros, frequency of chlorine use, and number of male and female black rhinoceros at a zoo simultaneously. Birth and death rates for each institution were calculated from studbook records. We found that the breeding success of a zoo since 1973 correlated positively with enclosure area, and zoos with two or more females had a lower reproductive rate than zoos with only one female. Females residing during their pre-reproductive years at a zoo with another reproductive female gave birth for the first time on average 3 years later than sole females. Mortality since 1973 correlated positively with percentage of public access. In Part I, we developed behavior profiles of 29.31 individual black rhinoceros from keeper ratings. Scores for males on the behavior trait Fear also correlated positively to percentage of public access, and we suggest that this aspect of black rhinoceros exhibits is a stressor for this species, especially the males. We found that different aspects of captive environments are associated with male and female black rhinoceros behavior. Male scores on the behavior trait dominant were higher in smaller enclosures, and female scores for a group of behaviors suggesting agitation (chasing/stereotypy/mouthing) were positively correlated with percentage of walls in their enclosure. These two behavior traits were found in Part I to be negatively correlated with the breeding success of an individual male or female. We re-surveyed the behavior and husbandry of 29 black rhinoceros pairs in zoos 2 years after the original data were collected. The re-survey confirmed that compatible black rhinoceros pairs are those with assertive females and submissive males, and that enclosure area and a low percentage of concrete walls around the enclosure are positive predictors of a pair's reproductive success. We conclude that temperament traits of individuals and characteristics of their captive environments both have an impact on a pair's breeding success. Our study demonstrates that cross-institutional comparisons of zoo facilities, when integrated with behavioral assessments of individual animals, are a valuable tool for investigating potential causes of poor reproduction and well-being in zoo animals. Zoo Biol 18:35–52, 1999. © 1999 Wiley-Liss, Inc.