In September 2024 an unusual mortality event (UME) was identified in a group (n=1000) of Radiated tortoises (AR) inhabiting an 8-hectare prerelease pen in Southwestern Madagascar. Prerelease protocols previously been used successfully in 3,000+ AR in Southeastern Madagascar had been followed with only minor deviations. Factors considered as contributions to a death rate of 19.4% compared to death rates in other prerelease pens of < 3% were: drought during the months after placement into the pen; infectious disease; environmental toxins (disproportionate numbers of toxic plants in the pen); and iatrogenic toxin (treatment with fenbendazole 3 weeks prior to translocation). As soon as the UME was discovered, the remaining tortoises were provisioned with food (sliced cactus) and water twice weekly. A team of Malagasy veterinary interns, at the site first, treated 806 tortoises with fluids and antibiotics. This was followed within several days of 4 expats with supplies for collection and storage of biological samples and additional medications as well as point-of-care instruments. Blood samples, choanal/cloacal swabs, necropsy tissues and plant samples were collected. Plants within and around the release pen were identified and catalogued by a botanist. Challenges of diagnosis, sample collection and treatment included environmental temperatures greater than 38℃. (Cold chain was maintained by a combination of liquid nitrogen tank, cold packs, coolers and a portable freezer run off solar power) and remote location of the tortoises requiring use of zebu-cart to transport equipment daily. The death rate has remained low since the intervention began.