Release criteria for rehabilitated wildlife should be based on evidence of survival fitness including appropriate weight, behavioral competency, and absence of conditions incompatible with wild survival.
The welfare case for rigorous release criteria is based on the recognition that releasing unfit animals extends their suffering rather than improving their welfare. A hedgehog released underweight before hibernation faces starvation during winter. A raptor released with impaired flight cannot hunt and starves. Mortality of released animals is expected but should be minimized through evidence-based release criteria and timing. When rehabilitation cannot restore adequate fitness for wild survival, the welfare decision must choose between permanent quality captive care and humane euthanasia. Releasing an animal to die slowly in the wild because humans cannot bring themselves to euthanize is not an animal welfare decision.