Animal Behavior/Penguin Loving
Compared with other birds, emperor penguins have everything backwards. They breed in winter, the females compete for the males, and they’re notoriously unfaithful. They’re the most bizarre birds I’ve ever met.
- -Ann Bowles in the article “Emperors of the Ice."
Emperor penguins, Aptenodytes forsteri, are the largest of the penguin family. They live in harsh environments of the Antarctic, battered by extreme weather conditions and vicious predators, and are the only warm-blooded animal to winter on the open ice. It is therefore no surprise that these birds present unique behaviors. The mating and brooding habits of these penguins reflect how these penguins have adapted to overcome these formidable obstacles.
Unlike other cohabitants of the Antarctic Circle, emperor penguins mate in the winter months of April and May. Males grow yellow tufts in the areas surrounding their ears, suspected of being an attraction factor for females. Unlike other species’ males that compete for nesting space and attract the females through quaint rituals (e.g. Adele penguin males throw scarcely available rocks at the feet of females to “get their attention”), emperor penguins do not create nest and put on mating displays that last for weeks, during which the future parents learn each other’s call. After copulation and, about 15 days later, the laying of a single, soft-ball sized egg, the female leaves to the sea where she embarks on a mission to feed well. Meanwhile, the father cares for the egg. To protect it from the frosty floor, for the next 6-8 weeks the father balances the egg on its two feet, under the protective blubbery flaps of its underbelly, to keep it warm. During the whole incubation period the father does not eat and may lose a third to half of its body weight.
The mother returns right before hatching (usually at the beginning of September), well-fed and with food for her offspring. The two parents apparently find themselves through distinguishable calls. Visual aids are useless in a crowd of 6000 penguins that all look similar. The mother then feeds the chicks for the first time, regurgitating some of the spoils caught while she was away. As the female broods the young, the father is free to replenish his energy, only to return to jointly rear the chick along with the mother.
The newly hatched chicks are barely protected from the sub-zero temperatures by their downy coats. Another important behavior, displayed similarly between adult penguins and chicks, is the formation of clustered groups called crèches. Within these groups the birds are able to maintain temperatures of about 96 degrees F, in contrast to the minus 30 degrees winds. So much heat is created in these crèches that the group must constantly move from location to avoid falling into the melted holes in the ice created by the heat generated by these crowds. This story ends when penguin chicks, huddled in groups at the edge of the sea, hop onto a recently broken-off chunk of ice and float towards the north to go on with their lives.
“How” do these behaviors occur? What are the proximate reasons of these behaviors? These breeding and brooding behaviors are influenced by many factors. Studies have shown that anatomical preparation for copulation is not stimulated by the mating displays, as is seen in other species. Penguins that reach the mating areas have seven times the normal amount of luteinizing hormone (LH), testosterone (in males) and estrogen (in females) upon arrival, suggesting that geographical or environmental cues activate gonodal preparation, specifically corresponding to maximum size of the gonads (1). Between copulation and egg-laying, levels of all hormones begin to fall, but LT remains slightly above average in incubating males, and in both males and females that are rearing their young. This leads to the conclusion that LT is responsible for incubating, brooding and territorial behavior. The hormone prolactin has also been linked to parental care (2).
Next question should be why these behaviors happen? What are the ultimate causes? Why do penguins endure the harsh Antarctic winter and choose to have their young during this apparently dangerous time? Speculation has lead to a few hypotheses. One is the lack of predators. These penguins are the only animals left during the winter’s cold. There are no leopard seals to menace the young. Another advantage of wintering the summer grounds is the first access to the abundance of food that the early warmer season brings. The quantity of food and the climate is perfect for the chicks to learn to fend for themselves. These two factors may have been enough evolutionary pressure to give rise to these vital behavioral traits in emperor penguins.
(1) Groscolas R, et al. “The endocrine control of reproduction and molt in male and female emperor and adelie penguins. I. Annual changes in plasma levels of gonadal steroids and LH.” Gen Comp Endocrinol, 62(1), pp 43-53.
(2) Lormee, Herve, et al. “Endocrine Correlates of Parental Care in an Antarctic Winter Breeding Seabird, the Emperor Penguin, Aptenodytes forsteri”. Hormones and Behavior, 35(1), pp 9-17.