White, Brent C., et al. “Faecal Glucocorticoid Concentrations During ACTH Challenge Tests in Captive Grizzly Bears (Ursus Arctos Horribilis) and Polar Bears (Ursus Maritimus)”. Journal of Zoo and Aquarium Research, vol. 3, no. 2, Apr. 2015, pp. 59-62, doi:10.19227/jzar.v3i2.116.