Operational Pain Indicators in Wild Birds in South America: Expert Consensus, Field Validation and Application in Rehabilitation Centres

Pain assessment remains a major challenge in avian medicine and wildlife rehabilitation because birds frequently exhibit subtle and species-specific responses that are difficult to detect under field conditions. The objective of this study was to identify, validate and operationalise indicators suitable for assessing pain in wild birds admitted to rescue, rehabilitation and zoological facilities. A four-phase approach was used, including a literature review, expert validation, field validation and the development of a Bird Pain Index (BPI). Scientific publications indexed in Scopus and Web of Science were reviewed to identify candidate pain indicators. Then, veterinarians, wildlife rehabilitation professionals, zoo personnel, ornithologists and animal welfare specialists evaluated the relevance, magnitude and applicability of each indicator using structured questionnaires. Forty candidate indicators were initially identified through the literature review; following expert assessment, only 25 indicators exceeded the acceptance threshold (>60%) for field validation. Nine indicators were ultimately validated as Operational Pain Indicators (OPIs) based on high field feasibility: isolation behaviour (78%), half-closed eyelids (75%), anorexia (73%), stillness (70%), loss of grooming (67%), miosis/mydriasis/anisocoria (67%), seated posture (65%), ruffled feathers (64%), and pain concealment behaviour (62%). Most validated indicators were behavioural or clinical measures that could be assessed without handling the animals, while physiological indicators generally showed lower field applicability. The validated OPIs were integrated into a preliminary BPI designed to support clinical decision-making and welfare assessment.