Clinicopathologic Features of Stress-Associated Sudden Death in Three Captive Crested Ibis (Nipponia nippon)

The endangered crested ibis (Nipponia nippon), once reduced to just seven individuals in the wild worldwide in 1981, has rebounded to more than 10,000 through intensive conservation. Yet the species remains highly vulnerable to acute environmental disturbance, with stress-induced sudden death (SISD) posing persistent challenges for captive management and reintroduction programs. We investigated three SISD cases, integrating behavioral context with necropsy and histopathology in all cases, and computed tomography/magnetic resonance imaging neuroimaging and metagenomic pathogen screening in a subset. Major organs showed no diagnostic lesions, with only mild, nonspecific digestive tract changes. Neuroimaging identified localized subdural hemorrhage without diffuse parenchymal damage. Metagenomic screening detected no high-pathogenicity avian viruses, fungi, or parasites and only trace environmental bacteria. Using published datasets, we also compared baseline corticosterone (CORT) from feathers and blood across five avian species; crested ibis occupied the lower end of baseline CORT distributions, consistent with reduced endocrine buffering capacity. These observations suggest that peracute death may occur in association with acute disturbance even in the absence of overt infectious or major degenerative lesions, with panic flight and collision trauma likely contributing to the terminal events. Framing SISD as a failure of physiological tolerance thresholds highlights actionable management: minimizing startle stimuli, reducing predator cues and human disturbance during sensitive periods, carefully staging transfers to new enclosures, managing group dynamics to limit social transmission of stress, designing for safe flight, and early-warning monitoring. Taken as case-based evidence, this work may help refine captive husbandry and reintroduction protocols aimed at improving survival and long-term population resilience.