Role of transit countries in global illegal wildlife trade

Illegal wildlife trade is an important branch of global environmental crime. It relies heavily on transit countries to promote the cross-border movement of illegal wildlife products by boosting markets, laundering services, processing and packaging products, and concealing routes. However, transit countries' strategic role is not well understood. We constructed a dataset of 15 years of illegal wildlife seizure cases from the Center for Advanced Defense Studies (C4ADS) air seizure database and Wildlife Trade Portal database. From the dataset, we determined transnational illegal wildlife trade routes with complete supply chain information. There were 84 transit countries, and the organisms involved in trade included mammals, birds, reptiles, marine species, amphibians, and arthropods. We identified that about 40% of illegal wildlife trade routes crossed one or multiple countries. Species being moved along these routes originated mainly from Africa and were transported through African, European, or Asian countries to East Asia or Southeast Asia. Transit countries for illegal wildlife products tended to be geographically close to and have a high trade volume of legal biological products with both the origin and destination countries and had advanced airport infrastructure. Transit countries were associated with 39.7% more individual animal products being illegally traded, particularly ivory, pangolin products, and rhinoceros horn, and served as key bridges among economically underdeveloped and geographically distant countries with weak trade links in legal biological products. These findings highlight the importance of monitoring and enforcement in transit countries and suggest that transit hubs be targeted based on location, trade in legal biological products, and transport infrastructure.