Continuous enhancement in management, care, and welfare in great apes in zoological institutions as evidenced by survival summary metrics

Survival-related metrics are commonly used as a proxy of population-level welfare as studies have reported that happier and healthier individuals live longer. Here, we studied the change in two key survival summary metrics – the life expectancy and the lifespan equality of a population – proved to be a reliable proxy of population welfare in human and non-human animals (for example, see our previous research on the improvement of population welfare in zoological institutions for four marine mammal species, Tidière et al. 2023).

The reports emphasize advancements in husbandry and management practices made by accredited zoological institutions over the past century for four great ape species—lowland gorilla (Gorilla gorilla), chimpanzee (Pan troglodytes), Sumatran orangutan (Pongo abelii), and Bornean orangutan (Pongo pygmaeus). These improvements are evident in the significant increase in life expectancy and lifespan equality of these species.For example, chimpanzees' average life expectancy has increased from approximately 7 years in the early 1900s to around 30 years today—a 4.3-fold improvement in 100 years. This underscores the proactive behaviour of accredited institutions in constantly improving their management practices.

While improvements in life expectancy and lifespan equality reflect positive changes in living conditions and overall welfare, they do not alone guarantee individual welfare. Each animal's unique experience and personality may affect how well they thrive under improved conditions. Therefore, it remains crucial to focus on individual welfare to ensure all animals benefit from enhanced care standards. Rigorously capturing data on individual welfare, as done in the ZIMS Care & Welfare module, is vital for improving the quality of life for animals in zoological institutions.

Ensuring the survival of threatened species requires a multifaceted approach. Accredited zoological institutions are at the forefront of this effort, bridging the gap between the wild and human society to preserve biodiversity. This research contributes to the ongoing discourse on animal welfare and may inform future policy decisions, underscoring the importance of biology-informed husbandry, resource investment, and scientific research.