Reintroductions are increasingly being proposed as a valuable conservation measure with the potential to save many species from extinction. However, some people have criticised them due to their low success rate and high costs. Previous reviews found that the average success rate of reintroductions ranges from 11 to 53%. It is essential, thus, to further investigate and improve reintroduction methods in order to ensure their viability.
There are various biological and ecological factors that contribute to the success or failure of a reintroduction project. Some examples are the habitat suitability, the availability of food in the long-term, the season of release and the type of release (soft or hard). Another important factor affecting the success is the origin of the source population (wild-caught or captive-born animals).
Wild-caught versus captive-born
Reintroduction projects for the purpose of conservation are carried out because wild populations are declining. Thus, reintroduction projects are increasingly sourcing individuals from captive populations. However, the reintroduction of captive animals have associated many problems.
Animals in captivity often show a loss of natural behaviors needed for success in the wild. For example, they can show deficiencies in foraging/hunting, social interactions, breeding and nesting, and locomotory skills. Furthermore, captive-born animals are more susceptible to viruses and diseases due to lack of immunities.
In order to quantify these deficiencies, a study reviewed 45 carnivore reintroductions worldwide. The study analyzed the success of reintroduction projects depending on the source of animals (i.e. wild-caught individuals obtained from a sustaining wild population or from captive breeding stocks).
Reintroduction success rate in carnivores
The study found that reintroduction projects were significantly more likely to succeed when they used a wild source population compared to a captive source. Captivity negatively influences carnivores’ capabilities to survive, and in many cases resulted in a lack of appropriate “wild” behaviours.
For example, captive individuals lack of hunting/foraging skills and lack of fear towards humans, which are major disadvantages. That is especially relevant, as human means was the most common cause of death, including shooting, poisoning and vehicle collisions. Captive-born carnivores were also more likely to starve to death than their wild-bred counterparts, as well as become more susceptible to viruses and diseases.
Is the use of wild source populations the solution? Well, the reality is that there are not many sustainable carnivore populations left in the wild to provide release stock. Thus, in many cases, the use of captive populations, either to establish a new population or to supplement existing populations, is the only viable option. Therefore, there is a need to further investigate the factors affecting success rates between wild and captive source populations needs. We have to improve reintroduction techniques to increase the survival of captive-born released carnivores. For example, researches argue for better pre-release training to improve hunting skills and adjust to natural social groups, and better selection criteria for choosing animals for release (e.g. bold animals toward humans are more likely to die).
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