Black rhinoceros (Diceros bicornis) in US zoos: II. Behavior, breeding success, and mortality in relation to housing facilities

The captive population of black rhinoceros (Diceros bicornis) is not self-s ustaining. The reasons for suboptimal reproduction and high mortality need to be investigated. This can only be achieved by cross-institutional analys es of environments, behavior, and performance. In this study, we collected data on 23 toes with black rhinoceros to compare zoo environments with repr oductive success, mortality, and behavior. Institutional variation was char acterized by enclosure area, percentage of walls around enclosure perimeter , percentage of public access along enclosure perimeter, climate, noise lev el, number of years zoo has maintained black rhinoceros, frequency of chlor ine use, and number of male and female black rhinoceros at a zoo simultaneo usly. Birth and death rates for each institution were calculated from studb ook records. We found that the breeding success of a zoo since 1973 correla ted positively with enclosure area, and toes with two or more females had a lower reproductive rate than toes with only one female. Females residing d uring their pre-reproductive years at a zoo with another reproductive femal e gave birth for the first time on average 3 years later than sole females. Mortality since 1973 correlated positively with percentage of public acces s. In Part I, we developed behavior profiles of 29.31 individual black rhin oceros from keeper ratings. Scores for males on the behavior trait Fear als o correlated positively to percentage of public access, and we suggest that this aspect of black rhinoceros exhibits is a stressor for this species, e specially the males. We found that different aspects of captive environment s are associated with male and female black rhinoceros behavior. Male score s on the behavior trait dominant were higher in smaller enclosures, and fem ale scores for a group of behaviors suggesting agitation (chasing/stereotyp y/mouthing) were positively correlated with percentage of walls in their en closure. These two behavior traits were found in Part I to be negatively co rrelated with the breeding success of an individual male or female. We re-s urveyed the behavior and husbandry of 29 black rhinoceros pairs in toes 2 y ears after the original data were collected. The re-survey confirmed that c ompatible black rhinoceros pairs are those with assertive females and submi ssive males, and that enclosure area and a low percentage of concrete walls around the enclosure are positive predictors of a pair's reproductive succ ess. We conclude that temperament traits of individuals and characteristics of their captive environments both have an impact on a pair's breeding suc cess. Our study demonstrates that cross-institutional comparisons of zoo fa cilities, when integrated with behavioral assessments of individual animals , are a valuable tool for investigating potential causes of poor reproducti on and wellbeing in zoo animals. (C) 1999 Wiley-Liss, Inc.