A 25-Year Retrospective Review of Mortality in Chimpanzees (Pan troglodytes) in Accredited U.S. Zoos from a Management and Welfare Perspective

SIMPLE SUMMARY: To improve the lives of chimpanzees living in managed care, it is important to understand why their lives have ended. Previous efforts to document the causes of death for chimpanzees living in research facilities have been useful; however, interpretations need to consider the relatively small number of facilities assessed, the recency of those evaluations, and the possibility that mortality rates were affected by experimental interventions at these sites. Here, the causes of death of 224 chimpanzees at 42 accredited zoos over a 25-year period were analyzed. Most of the chimpanzees over 1 month of age died from causes associated with degenerative diseases (50%), infection (26%), and trauma (15%). Causes of fatal trauma ranged from aggression from conspecifics, the outcomes of exhibit escapes, or accidental drowning. The number of accidental deaths has decreased in the past decade, likely as a result of advances in exhibit design and management. Cardiopulmonary problems have long been known to be prevalent within the chimpanzee population, and they remain a major contributor to death for both sexes in this population. Understanding these findings provides an opportunity to improve the care and management of captive chimpanzees. ABSTRACT: Understanding causes of death allows adjustment of health management strategies for animals in managed care. From 224 documented chimpanzee deaths occurring from 1995 to 2019 in 42 accredited U.S. zoos, post-mortem records and necropsy reports were analyzed for the primary cause of death, which were available for 214 individuals. In total, 37 cases of stillbirth and neonatal deaths were assessed (16.5%); however, the focus was otherwise placed on the remaining 177 cases in which the death occurred in individuals aged greater than 1 month. There were no sex-related differences in etiology; however, age variation in the cause of death was statistically significant (p < 0.001). Elderly (35 years and older) chimpanzees tended to die of intrinsic, often degenerative, etiologies, whereas infants, juveniles, and adolescents (less than 15 years) were more likely to be involved in fatal trauma. Overall, there were 27 deaths (15.3% of all post-neonatal deaths) related to trauma and 13 of these were directly or indirectly related to conspecific aggression. Understanding causes of mortality and the interrelation with management can benefit managed populations of chimpanzees.