Survival of Captive Chimpanzees: Impact of Location and Transfers

To inform the retirement of NIH-owned chimpanzees, we analyzed the outcomes of 764 NIH-owned chimpanzees that were located at various points in time in at least one of 4 specific locations. All chimpanzees considered were alive and at least 10 years of age on January 1, 2005; transfers to a federal sanctuary began a few months later. During a median follow-up of just over 7 years, there were 314 deaths. In a Cox proportional hazards model that accounted for age, sex, and location (which was treated as a time-dependent covariate), age and sex were strong predictors of mortality, but location was only marginally predictive. Among 273 chimpanzees who were transferred to the federal sanctuary, we found no material increased risk in mortality in the first 30 days after arrival. During a median follow-up at the sanctuary of 3.5 years, age was strongly predictive of mortality, but other variables - sex, season of arrival, and ambient temperature on the day of arrival - were not predictive. We confirmed our regression findings using random survival forests. In summary, in a large cohort of captive chimpanzees, we find no evidence of materially important associations of location of residence or recent transfer with premature mortality.