Reference

Bricher PK, Lucieer A & Woehler EJ (2008). Population trends of Adélie penguin (Pygoscelis adeliae) breeding colonies: a spatial analysis of the effects of snow accumulation and human activities. Polar Biology 31(11):1397–1407.
Trathan PN, Garcìa-Borboroglu P, Boersma D, Bost CA, Crawford RJM, Crossin GT et al. (2015). Pollution, habitat loss, fishing, and climate change as critical threats to penguins. Conservation Biology 29(1):31–41.