Evidence for a Metabolic Trap and Habituation Limiting Post-Release Survival of Orphaned Grizzly Bears

The rehabilitation of orphaned grizzly bear (Ursus arctos) cubs of the year is often driven by public and animal welfare considerations, yet its efficacy as a functional conservation tool remains poorly understood. This study evaluates a five-year (2019–2023) captive-rear and release initiative in British Columbia (BC), Canada, representing the only systematically monitored program of its kind in North America. I monitored 14 orphaned cubs to examine how age of entry, captive-rearing duration, social environment (number reared together), and body mass at release influenced post-release survival. Of these, 13 bears were subsequently monitored post-release. These releases also provided a unique opportunity to examine whether greater release mass confers a survival advantage, a relationship previously suggested to reduce predation risk in captive-reared ursids. Results were benchmarked against morphometric data for wild yearlings in western North America. Captive-reared yearlings (n = 14) exhibited significant physiological divergence; mean spring release mass (127.4 kg) was 3.5-fold greater than wild-reared counterparts (36.1 kg; p < 0.0001). Despite this size advantage, the confirmed mortality rate was 83% among bears with known outcomes (n = 10/12). Mortality was heavily concentrated in the short-term, with 75% of the bears failing to survive from release to first denning. Contrary to rehabilitation best practices, minimizing handlers did not prevent habituation; several bears quickly generalized human presence with food security post-release. Survival was inversely related to captivity duration; increased time in captivity, driven by earlier age of intake, was associated with reduced survival, likely reflecting the combined loss of maternal learning and prolonged habituation. Furthermore, the relationship between release mass and survival was non-linear; individuals exceeding 135 kg consistently failed to recruit, suggesting a ‘metabolic trap’ where oversized frames create energetic demands difficult to meet for naïve yearlings foraging without maternal guidance in resource-limited spring landscapes. If rearing protocols diverge too far from natural conditions, facilitating habituation through routine husbandry and producing developmental outliers, rehabilitation remains a form of sympathetic management rather than a conservation tool. I advocate for species-tailored, “hands-off” protocols that prioritize natural growth trajectories and behavioural wariness during captive-rearing.