van Oort, B. E.H., N. J.C. Tyler, E. Reierth, and K.-A. Stokkan. “Biological Rhythms in Arctic Vertebrates”. Rangifer 20, no. 2-3 (March 1, 2000): 99-112. Accessed September 25, 2020. https://septentrio.uit.no/index.php/rangifer/article/view/1506.