Thomas, David N., G.E. (Tony) Fogg, Peter Convey, Christian H. Fritsen, Josep-Maria Gili, Rolf Gradinger, Johanna Laybourn-Parry, Keith Reid, and David W.H. Walton. "Birds and mammals in polar regions." The Biology of Polar Regions. : Oxford University Press, 2008-03-20. Oxford Scholarship Online. 2008-05-01. Date Accessed 24 May. 2013 <http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199298112.001.0001/acprof-9780199298112-chapter-9>.
Thomas, D., Fogg, G., Convey, P., Fritsen, C., Gili, J., Gradinger, R., Laybourn-Parry, J., Reid, K., & Walton, D.(2008-03-20). Birds and mammals in polar regions. In The Biology of Polar Regions. : Oxford University Press. Retrieved 24 May. 2013, from http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199298112.001.0001/acprof-9780199298112-chapter-9.
Thomas, David N., G.E. (Tony) Fogg, Peter Convey, Christian H. Fritsen, Josep-Maria Gili, Rolf Gradinger, Johanna Laybourn-Parry, Keith Reid, and David W.H. Walton. "Birds and mammals in polar regions." In The Biology of Polar Regions. : Oxford University Press, 2008-03-20. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199298112.001.0001/acprof-9780199298112-chapter-9.
Thomas DN, Fogg G(, Convey P, et al. Birds and mammals in polar regions. In: Thomas D, Fogg G, Convey P, et al. The Biology of Polar Regions. Oxford University Press; 2008. http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199298112.001.0001/acprof-9780199298112-chapter-9. Accessed May 24, 2013.