Insights on the translocation of a critically endangered crocodylian: Diet and body condition of headstart and wild Philippine crocodiles (Crocodylus mindorensis)

Abstract

Studies of diet are fundamental to understanding a species’ ecology, and in relation to conservation translocations, dietary studies of headstart populations are particularly rare and valuable. These studies can yield insights into effects of headstarting on a population's ability to adjust and become established in the wild. With less than 150 mature individuals remaining in the wild, the critically endangered Philippine crocodile (Crocodylus mindorensis) is one of the most severely threatened species on the planet. We conduct the first analysis of stomach contents and characterize the diet of Philippine crocodiles from Isabela Province on the island of northern Luzon, Philippines. Additionally, we address concerns regarding captive-release programs by analyzing stomach contents of headstart crocodiles released into the wild over the last decade. Our study of diet from a resident wild population (N = 20) acts as a baseline comparison for evaluating the dietary habits of headstart crocodiles (N = 10), from which we found no evidence for dietary differences in percent occurrence, percent composition, and prey diversity. Overall, we demonstrate the use of 17 different prey species across eight prey categories (snails, fish, birds, reptiles, amphibians, mammals, crabs, and insects). Finally, we calculate the first body condition index (Relative condition factor Kn) for C. mindorensis and examine variation in body condition between headstart and wild crocodiles and find that wild crocodiles have significantly higher condition scores than headstart individuals. Overall, headstart crocodiles adjust well post-release and exhibit similar dietary habits compared to their wild counterparts, even within an agriculturally dominated landscape where they are likely exploiting the high abundance of the golden apple snail, an invasive species and the leading agriculture pest in the Philippines. Our focused monitoring methods reveal broader relevance for conservation, highlighting the importance for a long-term commitment to both ecological monitoring and enhancing the capacity of in-country local communities.