Bryant, Jocelyn, and Terri Roth. “Annual Fecal Glucocorticoid Metabolite Concentrations in Pregnant and Pseudopregnant Polar Bears (Ursus Maritimus) in North American Zoos”. Journal of Zoo and Aquarium Research, vol. 6, no. 1, Jan. 2018, pp. 6-11, doi:10.19227/jzar.v6i1.259.