The notion that penguins might behave like lotharios, sequentially seducing a bevy of partners, runs counter to the popular image of these famously monogamous and endearing creatures. Moreover, to even suggest that some of them might actually cheat on their partners—have an affair, in our parlance—seems to stretch the bounds of belief, to tar the penguins with our own sins. The view that penguins are more upright than us, morally, if not also in their stance, is as prevalent in science as much as it is in society.
There are several factors that make divorce in Antarctic penguins from one season to the next seem, if not morally admirable, then at least understandable. Their imperative is to breed. Their chances of success are slight. Not only is there high mortality of eggs and chicks, but the great majority of chicks that fledge do not survive to reproduce. In a Darwinian sense, most breeding attempts are dead ends. Storms, predation, the amount of ice cover, the location, and amount of food are all factors that influence breeding success but are variable and largely outside the control of the birds. The one factor that the penguins can control is when they breed. The best predictor of whether a chick will survive to reach reproductive age is how big it is when it fledges. In other words, to have any reasonable chance of being successful, parents need to get cracking with breeding as soon as the conditions are favorable to do so. It would be Darwinian suicide to wait for a previous partner and delay breeding, even if that tardy partner is alive.
On the other hand, once penguins have paired for the season, surely they should stick with it. They don’t need to mate together for the rest of their lives, but surely they can and, in their best biological interests, should be faithful for a year? Is that too much to expect?