The Pygmy Hippopotamus Choeropsis liberiensis (Morton, 1849): Bringing to Light Research Priorities for the Largely Forgotten, Smaller Hippo Species

An endangered species, the pygmy hippo (Choeropsis liberiensis Morton, 1849) has been housed in captivity since the early 1900s, but systematic, prospective research and peer-reviewed literature remain limited in comparison to other IUCN-listed, charismatic mega fauna. There are just over 350 animals in the ex situ population worldwide, so it is an uncommon resident in zoological collections compared to the larger, ‘common’ or Nile hippo (Hippopotamus amphibius). Most published information for the pygmy hippo constitutes descriptive accounts of first-hand experiences in various zoological institutions. Here we review, analyze and provide a synthesis of the pertinent literature, aiming to identify and prioritize focal research topics for optimizing ex situ management. The pygmy hippo is continually reported to breed well and thus long-term survival of the species, at least in captivity, is assumed, although we identify several reasons to exercise caution. Further, we demonstrate that the common perception amongst zoological institutions that the pygmy hippo is easy to manage and experiences limited health and husbandry issues is erroneous. Specific issues affecting the captive population with potential negative implications for long-term sustainability include polycystic kidney disease (PKD), a female-biased sex ratio, obesity, a high neonatal mortality rate, and failure of many breeding pairs to reproduce. We identify several research priorities to help address these concerns, and how the resulting information can be applied to improve management, health and welfare of pygmy hippos in captivity.