Penguin bullies make chicks' lives hell
King penguin chicks agonise through a harrowing existence, according to a new detailed study of their lives.
Because king penguin adults are so aggressive, their chicks must band together in extremely tight-knit groups to survive.
The study, published in a recent issue of the journal Animal Behaviour, found that youths at the periphery of these groups, called creches, are at such high risk of being bullied and predated that they never fully go to sleep.
Instead, the chicks go into a sort of half-sleep, half-awake mode where they must open and close their eyes throughout a "vigilant sleep" cycle.
"Sleeping penguins alternate periods of eye closure with short periods of eye-opening, referred to as 'peeks' in their vigilant sleep," explains Dr Michel Gauthier-Clerc, one of the study's authors.
"Despite being in a sleeping posture during vigilant sleep, penguins may scan their surrounding environment."
Gauthier-Clerc, a scientist at the Tour du Valat biology station in Arles, France, and his colleagues studied over 16,000 king penguins (Aptenodytes patagonicus) on Possession Island, Antarctica.
Adult penguins often used their flippers to peck or bash chicks abandoned by one or both parents. These chicks ran toward other youths until circular creches formed.
Chicks scrambled for a position in the center of the creche. Short, lightweight birds were pushed to the circle's outer limits where they often were attacked and eaten by giant petrals, brown skuas and kelp gulls.
While chicks in the relatively warm and safe center of the creche slept soundly, birds at the periphery only rested during their vigilant sleep cycles.
Gauthier-Clerc says that sleep is an energy-saving process essential for all vertebrates, including humans. While some shut-eye is better than none, the blinking, bullied penguins on the outside of creches become disadvantaged once again.
"We can make the hypothesis that a chick at the periphery saves less energy because it is colder and the chick sleeps less," he says.
"For a penguin in the periphery, the individual is not protected from the wind, it is less protected from predators, and it sleeps less. Its body condition will probably be lower."
He indicates the chicks must live like this, and without food, for the entire winter, until the parents hopefully return at the end of the season with food.
Professor Charles Amlaner of Indiana State University, who has also studied king penguins, says the findings "are consistent with much that we know about creches and creching behaviour".
Amlaner says he only has one slight disagreement with the researchers, who say "sleep and vigilance are mutually exclusive".
Amlaner says his team has studied the brains of other birds while they went through vigilant sleep, and it seems that the birds simultaneously experienced the benefits of being awake and asleep.
"The closed eye and sleeping half of the brain allows the benefits of sleep to be gained while at the same time, the open eye and awake half of the brain allows the bird to remain vigilant to potential predation," he says.