Fluctuations and Sex Differences in Food Consumption Relative to Molting in Magellanic Pegnuins (Spheniscus magellanicus) at San Francisco Zoo

Our objective was to measure food intake of adult Magellanic penguins as they fatten up before molting, fast while molting, and regain condition afterwards. In late summer and early fall every year Magellanic penguins shed all their old feathers and grow new ones. Unable to enter the water without mature feathers for insulation penguins fast while molting, and to survive the fast and grow new feathers they build up fat stores beforehand. Using data from San Francisco Zoo, we analyzed fish consumption of 29 female and 26 male penguins for 60 days before the onset of molt and 40 days after. Data were standardized for analysis by designating the first day of molt Day Zero for every bird. Food intake started increasing noticeably 50 days before molt began, doubled—going from 200 to 400 g—over the next 30 days, and then more than doubled again in the following 20 days. While Magellanic penguins in the wild would not eat at all while molting, at the zoo they did but mean daily consumption dropped to 50 g for both sexes. Molt took 21 days, following which food consumption increased sharply, quadrupling over the next 20 days for both sexes, and then beginning to level off