Evaluation of the stress state based on fecal corticosterone metabolite concentrations in captive penguins in Japan.

Fecal corticosterone metabolite (FCM) concentrations, which can be determined noninvasively, have recently been explored as a stress indicator in birds. In our study, we measured FCM concentrations in penguins under nonmolting or molting conditions, cool or hot season, diseased condition, and incubation period. These measurements were conducted in an aquarium that housed king penguins, gentoo penguins, and African penguins. This study aimed to investigate the validity of fecal matter as a stress indicator. Our findings revealed that FCM concentrations were significantly higher in molting individuals than in nonmolting individuals. Compared with the cool season, FCM concentrations were significantly higher in penguins housed outdoors during the hot season. However, no differences were observed in penguins housed indoors. Diseased individuals and an incubating individual showed notably higher FCM concentrations than healthy individuals. Interestingly, the FCM concentration in king penguin that underwent cataract surgery was extremely high before the surgery. However, 1 month postsurgery, it decreased to a level similar to that of healthy individuals. We observed increased FCM concentrations in penguins considered to be exposed to stressors. Notably, FCM concentration decreased after removing the stress factor. The FCM concentration was found to be consistent with the stress state of penguins, suggesting its usefulness as a stress indicator.