Using mortality and reproduction data to evaluate captive penguin nutrition

Source: R. Pizzi, M. Gibbons, A.M. Wood, G. Mackenzie, M.C. Garcia-Rueda, Royal Zoological Society of Scotland, Edinburgh Zoo, UK
While evaluating diets fed to penguins in captivity with that consumed by wild birds would be ideal, there is a paucity of much relevant knowledge.
Little nutritional analysis of Notothenioid fish species has been performed. The small amount of lipid and vitamin analysis in Antarctic krill Euphausia superba, the predominant prey of numerous penguin species, has shown marked variation in nutritional content, dependant on season, gender, and life stage of krill. It is also known that some penguin species can discriminate and actively consume gravid female krill, further complicating extrapolation to captive diets. Instead a combination of needs extrapolated from domestic poultry, other fish eating vertebrates, and partial knowledge of wild diets has previously been used. Penguins have been kept for over a hundred years in Edinburgh zoo. A large closed population of King penguins Aptenodytes patagonicus, Gentoo penguins Pygoscelis papua, Macaroni penguins Eudyptes chrysolophus, and Rockhopper penguins Eudyptes chrysome, has been maintained for the last 40 years. This appears to be the largest long-term self-sustaining captive penguin population in the world, and offers a unique opportunity for nutritional research. Of the more than 1200 penguin post-mortem examinations performed at Edinburgh zoo, 813 post-mortem examinations have been performed in the last 40 years, 635 of which are of a single species, the Gentoo penguin Pygoscelis papua. Analysis of mortality and disease incidence patterns, as well as reproductive success have been correlated with dietary changes, as a different method of trying to determine the impact of captive nutrition. The adult gentoo penguin population has shown a significant rise (p<0.01) in mortality rate between 1964-2003 (95%CI of gradient: 0.12-0.51). The median age at death of adult gentoo penguins has fallen from 8 years (95%CI 7-10, n=199) during the period 1980-1990 to 5 years (95%CI 3-8, n=118) during the period 1993-2003. Interesting findings, confounding factors, and limitations will be discussed.