Patterns of acceptance of artificial eggs and chicks by Magellanic Penguins (Spheniscus magellanicus)

Life history theory predicts that parents will not raise unrelated offspring. For seabirds, an ability to recognize their own eggs and chicks can prevent a costly mistake. We tested whether Magellanic Penguins (Spheniscus magellanicus) would discriminate against artificial eggs by presenting nine types of egg-objects and one type of artificial chick to penguins at their nests. Magellanic Penguins regardless of their sex or breeding status accepted all egg-objects. A generalized linear mixed model showed that mass and number of dimensions were the most important factors in predicting whether the object was accepted: flat egg-objects and light egg-objects were less likely to be incubated than round, normally weighted ones. We also tested whether Magellanic Penguins would retrieve egg-objects more frequently if the object was within 1 m of the nest cup. Penguins retrieved 75 % of objects that were 1 m from the nest cup, but only 25 % of objects that were 2 m from the nest cup. Lastly, we tested whether penguins would accept artificial chicks. We found that pairs with chicks less than 3 weeks of age (i.e., not out of the guard stage) were at least twice as likely to brood an artificial chick than pairs with chicks older than 3 weeks, pairs that had lost their chicks, or unmated males.