On December 9th, 2022, the Biodôme’s penguin care team discovered an egg under the female king penguin. As no bonding nor nesting behavior was observed with any of the male king penguins, it was presumed that the egg was unfertilized. However, on the morning of January 31st, the penguin caretakers got quite the surprise: a cheeping chick was busy digging its way out of its shell to hatch! What happened over those 54 days, unbeknownst to the entire Biodôme team? A life was taking shape in that incredible enclosure, the egg…
Production of an egg
Within the highly diverse animal kingdom, multiple reproductive strategies exist. Among them, the production of an egg that is capable of surviving without blood supply from the mother is a true evolutionary masterpiece. In birds, the ovary produces an ovum, which contains the protein-rich yolk of the egg. Then, that ovum continues its journey through the oviduct and the albumen, the egg white, accumulates around it to store a large amount of water. Subsequently, the formation of the contour membranes gives the egg its characteristic ovoid shape. The final but critical stage occurs when the shell gland in the uterus deposits calcium carbonate on the surface to form the protective armor-like shell. Thus, once it’s laid, the egg has all of the nutrients needed for the development of a chick, as long as it is kept warm by a parent, a stage known as incubation (or brooding). The duration and temperature required vary from one species to the next, but it essentially begins with the development of a vascular network in the egg: these vessels will run along the inner wall of the shell to ensure gas exchanges and nourish the embryo with oxygen. With all these elements – oxygen, warmth, proteins and water – life can begin!
The egg, the one, in the king penguin (Aptenodytes patagonicus) is not laid in a nest; instead, it is carried on the adults’ feet and is protected by an incubation pouch. The male and female take turns to incubate the egg until it hatches, which occurs at about 55 days after the laying. Once the chick has emerged from its shell, the parents carry on this joint custody. While one of the parents goes off fishing at sea to build up reserves for feeding the hatchling, the other fasts on dry land and keeps watch over the chick. When the parent that was gone fishing returns to terra firma, it has to locate its partner and chick among several thousand individuals on the move. And to complicate things, it’s been demonstrated that king penguins are unable to visually distinguish one from another (Jouventin, 1982). So how do they find each other?
The cocktail-party effect
In fact, it is only thanks to their call that the male, the female and their chick are able to find each other. But how do they manage to hear one another amidst the brouhaha of the entire colony? The study of this question has shown that chicks are able to discriminate their parents’ call among all the others, even if it is lower in intensity than the surrounding noise produced by the calls of other individuals (Aubin & Jouventin, 1998). This ability to filter out and extract relevant sound information from ambient noise while remaining alert to ambient noise constitutes what has been called the cocktail-party effect in humans (Cherry, 1953). Indeed, it is the same mechanism, brought to light in the 1950s, which makes it possible to hold and follow a conversation in an environment where several other conversations are taking place simultaneously. At the Biodôme, the conversation between the little penguin and the other individuals of the colony is definitely under way!
Going a step further:
- Aubin & Jouventin, 1998, Proceedings of the Royal Society of London B. Cocktail-party effect in king penguin colonies. [pdf].
- Cherry, 1953. The Journal of the Acoustical Society of America. Some Experiments on the Recognition of Speech, with One and with Two Ears. [pdf].
- Jouventin, 1982, Advances in Ethology. Visual and Vocal Signals in Penguins, their Evolution and Adaptive Characters. Fortschritte der Verhaltensforschung: Advances in ethology, S24.
- Le Blanc & Claverie, 2016 Hermès, La Revue. Entre sensation et cognition: l’illusion explicative. [pdf].
- How Are Eggs Made? | Attenborough’s Wonder of Eggs | BBC Earth [video]
- How Birds Get Oxygen Inside Their Eggs | NPR’s Skunk Bear [video]