New insights into the huddling dynamics of emperor penguins
Résumé
Social thermoregulation is a cooperative strategy in which animals actively aggregate to benefit from the
warmth of conspecifics in response to low ambient temperatures. Emperor penguins, Aptenodytes forsteri,
use this behaviour to ensure their survival and reproduction during the Antarctic winter. An emperor
penguin colony consists of a dynamic mosaic of compact zones, the so-called huddles, included in a
looser network of individuals. To maximize energy savings, birds should adjust their huddling behaviour
according to environmental conditions. Here, we examined the dynamics of emperor penguin aggregations,
based on photo and video records, in relation to climatic factors. Environmental temperature,
wind and solar radiation were the main factors contributing to huddle formation. The analysis of individual
movements showed that birds originating from loose aggregations continually joined huddles.
Sometimes, a small number of birds induced a movement that propagated to the entire huddle, causing
its breakup within 2 min and releasing birds, which then integrated into looser aggregations. Different
parts of the colony therefore appeared to continually exchange individuals in response to environmental
conditions. A likely explanation is that individuals in need of warmth join huddles, whereas individuals
seeking to dissipate heat break huddles apart. The regular growth and decay of huddles operates as
pulses through which birds gain, conserve or lose heat. Originally proposed to account for reducing
energy expenditure, the concept of social thermoregulation appears to cover a highly dynamic phenomenon
that fulfils a genuine regulatory function in emperor penguins.