Reintroduction - Successes and Failures

Successes and Failures

Reintroduction biology is new and continues to be a work in progress. The IUCN/SSC Re-introduction Specialist Group & Environment Agency, in their 2011 Global Re-introduction Perspectives, compiled reintroduction case studies from around the world. 184 case studies were reported on a range of species which included invertebrates, fish, amphibians, reptiles, birds, mammals, and plants. Assessments from all of the studies included goals, success indicators, project summary, major difficulties faced, major lessons learned, and success of project with reasons for success or failure. The Siberian tiger population has rebounded from 40 individuals in the 1940s to around 500 in 2007. The Siberian tiger population is now the largest un-fragmented tiger population in the world. Yet, a high proportion of translocations and reintroductions have not been successful in establishing viable populations Black Footed Ferrets in North America have also been a highly successful reintroduced species. Husbandry techniques were refined and the first successful captive breeding occurred in 1987. For this species, disease management in captivity is paramount and strict protocols are followed. Genetic management is closely monitored and ferrets are bred using a mean-kinship strategy which provides genetic diversity when breed in captivity. To prepare them for reintroduction into their new "wild" habitat, captive-born ferrets are placed in outdoor pens, simulating quasi-natural conditions with dirt burrows and live prey. Ferrets that receive pre-release conditioning in outdoor pens prior to release have demonstrated 10-fold higher survival rates in the wild than ferrets that receive no pre-release exposure. Ferrets are typically released in the fall during their natural dispersal and kits (young of the year) are the primary candidates.

Many factors can attribute to the success or failure of a reintroduction. Predators, food, pathogens, competitors, and weather can all affect a reintroduced population's ability to grow, survive, and reproduce. Animals raised in captivity may experience stress during captivity or translocation, which can weaken their immune systems. The IUCN reintroduction guidelines emphasize the need for an assessment of the availability of suitable habitat as a key component of reintroduction planning. Poor assessment of the release site can increase the chances that the species will reject the site and perhaps move to a less suitable environment. This can decrease the species fitness and thus decrease chances for survival. They state that restoration of the original habitat and amelioration of causes of extinction must be explored and considered as essential conditions for these projects. Unfortunately, the monitoring period that should follow re introductions often remains neglected.