The acute physiological response of polar bears to helicopter capture.

Many wildlife species are live captured, sampled, and released; for polar bears ( Ursus maritimus ) capture often requires chemical immobilization via helicopter darting. Polar bears reduce their activity for approximately 4 days after capture, likely reflecting stress recovery. To better understand this stress, we quantified polar bear activity (via collar-mounted accelerometers) and body temperature (via loggers in the body core [T abd ] and periphery [T per ]) during 2-6 months of natural behavior, and during helicopter recapture and immobilization. Recapture induced bouts of peak activity higher than those that occurred during natural behavior for 2 of 5 bears, greater peak T per for 3 of 6 bears, and greater peak T abd for 1 of 6 bears. High body temperature (>39.0°C) occurred in T per for 3 of 6 individuals during recapture and 6 of 6 individuals during natural behavior, and in T abd for 2 of 6 individuals during recapture and 3 of 6 individuals during natural behavior. Measurements of T abd and T per correlated with rectal temperatures measured after immobilization, supporting the use of rectal temperatures for monitoring bear response to capture. Using a larger dataset ( n  = 66 captures), modeling of blood biochemistry revealed that maximum ambient temperature during recapture was associated with a stress leukogram (7-26% decline in percent lymphocytes, 12-21% increase in percent neutrophils) and maximum duration of helicopter operations had a similar but smaller effect. We conclude that polar bear activity and body temperature during helicopter capture are similar to that which occurs during the most intense events of natural behavior; high body temperature, especially in warm capture conditions, is a key concern; additional study of stress leukograms in polar bears is needed; and additional data collection regarding capture operations would be useful.