A captive population in crisis: Testing hypotheses for reproductive failure in captive-born southern white rhinoceros females Ronald R. Swaisgood a, *, Dawn M. Dickman b,1 , Angela M. White a,2 a Conservation and Research for Endangered Species, Zoological Society of San Diego, P.O. Box 120551, San Diego, CA 92112, USA b Department of Biology, University of California, San Diego, La Jolla, CA 92093, USA ARTICLE INFO Article history: Received 1 September 2005 Received in revised form 10 November 2005 Accepted 18 November 2005 Available online 3 January 2006 Keywords: Conservation breeding Reproductive suppression Conservation behavior Reproductive behavior Rhinoceros ABSTRACT The captive southern white rhinoceros (Ceratotherium simum simum) population is not self- sustaining. Many founders reproduced, but reproduction among captive-born (F 1 ) females has been extremely sluggish. Thus the conservation breeding program for this species faces a looming crisis. Using behavioral observations of a large captive population and a questionnaire survey circulated to facilities worldwide, several hypotheses for F 1 female reproductive failure were evaluated. Counter to predictions regarding behavioral deficiency in sociosexual behaviors, F 1 females were at least as proficient as F 0 females for all behav- ioral measures. Males also showed no sociosexual preferences for F 0 over F 1 females. Results indicate that most reproductive failure occurs post-copulation. The reigning root- cause hypothesis for F 1 female reproductive failure postulates that F 0 females are behavior- ally dominant and suppress reproduction in F 1 females. However, no evidence for behav- ioral dominance was found and F 1 females housed with F 0 females were more likely to reproduce than those housed without F 0 females. Such social facilitation of reproduction is beneficial to F 1 female reproduction, but does not explain differential reproduction between F 1 and F 0 females. Because the design controlled for current conditions, these results point to development in captivity as the root cause of postcopulatory reproductive failure in F 1 females. Ó 2005 Elsevier Ltd. All rights reserved. 1. Introduction Captive breeding is a significant component of conservation to the extent that self-sustaining populations can be main- tained as a genetic reservoir should they be needed for rein- troduction or population supplementation (IUCN, 1998). Captive release programs have met with mixed success (Wolf et al., 1998; Fischer and Lindenmayer, 2000), yet can play a sig- nificant role in recovery of individual species (e.g., Frantzen et al., 2001; OÕToole et al., 2002; Wanless et al., 2002; Britt et al., 2003; Green et al., 2005). The World Conservation Union (IUCN) recommends that captive breeding programs should be established before the in situ population becomes so pre- carious that removals will exacerbate its decline. However, many captive populations are not self-sustaining and some continue to rely on removals of animals from the wild. For captive populations in crisis behavioral research can play a critical role in identifying and solving problems with breeding 0006-3207/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2005.11.015 * Corresponding author: Tel.: +1 619 744 3372; fax: +1 619 744 3346. E-mail address: rswaisgood@sandiegozoo.org (R.R. Swaisgood). 1 Current affiliation for Dawn D. Dickman: Lewis & Clark Law School, Portland, OR 97219, USA. 2 Current affiliation for Angela M. White: Environmental and Resource Sciences, University of Nevada Reno, Reno, NV 89512, USA. BIOLOGICAL CONSERVATION 129 (2006) 468 – 476 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/biocon