Releasing Rescued Animals Into the Wild Can Be Lethal - Slow Loris Study Shows Why

There is a comforting assumption built into wildlife rescue and release programs: that getting an animal back to its natural habitat is, by definition, a good outcome. A study tracking nine Bengal slow lorises released into a national park in northeastern Bangladesh has put that assumption under serious pressure.

Of the nine animals, only two survived. Three died within the first 10 days. Four more died within six months. Of the seven that died, four bodies were recovered - and all four showed bite wounds to the head, face, and digits consistent with fatal attacks by other slow lorises. The findings are published in the journal Global Ecology and Conservation, with researchers from Anglia Ruskin University, the NGO Plumploris e.V., and the University of Western Australia.

The territorial reality of slow lorises

Slow lorises are the world's only venomous primates. They are also highly territorial. Their sharp teeth, used to inject their venom, make them capable of inflicting serious wounds on competitors. The species is listed by the International Union for Conservation of Nature as Critically Endangered, Endangered, or Vulnerable depending on the specific loris species in question - designations that have made them a popular target for rescue and release projects.

Popularity of a release site can become a liability. The national park used in this study had been used for previous releases, meaning resident loris populations were already established at relatively high densities. Newly released animals - disoriented, lacking knowledge of local territory boundaries, and behaviorally altered by captivity - were entering a landscape where every territory was already occupied.

Captivity duration and survival

The study found that lorises that spent longer in captivity prior to release survived for fewer days in the wild. The released animals also showed elevated levels of movement and alertness compared to wild Bengal slow lorises - signs of stress and disorientation rather than the low-key, energy-conserving behavior that characterizes successful wild animals.

The two individuals that survived had a distinctive behavioral pattern: they moved to larger home ranges, apparently succeeding by pushing away from established territories rather than attempting to establish themselves within them. Their survival likely depended on finding unoccupied space - which in an already-saturated release site requires traveling further and faster than an animal should need to immediately after release.

A pattern likely extending beyond slow lorises

Lead author Hassan Al-Razi of Plumploris e.V. Bangladesh noted that release sites are often selected based on logistical convenience rather than ecological suitability, and that "certain forests have effectively become dumping grounds for rescued animals and are no longer appropriate release sites."

Unlike charismatic megafauna such as big cats - which typically receive intensive post-release monitoring - the fate of most rescued animals goes unreported. The slow loris study is unusual in having radio-tracked every individual to the point of death or confirmed survival. That rigor is exactly what makes the findings actionable: without tracking, the "successful" releases would simply have been lost to follow-up.

The researchers emphasize that these results do not argue against release programs in principle. They argue for site assessments that evaluate resident population density before selecting release locations, species-specific rehabilitation guidelines that account for territorial behavior, and long-term post-release monitoring as a standard requirement rather than an optional add-on.