At Tokyo Sea Life Park, we are sometimes asked, "Can you tell the difference between male and female penguins?" Males are slightly larger than females, but other than that, there are no other external differences, making it difficult to distinguish between males and females at a glance.

So, how do penguins distinguish each other? Birds have excellent color vision, so they may be using their vision to differentiate themselves in a world that looks different to humans. However, the reality is not well understood. But recently, some interesting behavior was observed among Southern Rockhopper Penguin during their breeding season.


Left: Male Right: Female
At Tokyo Sea Life Park, in order to allow the birds to behave as naturally as possible, males and females are separated once during the breeding season and then reunited at an appropriate time. During the separation period, the males secure the best possible location to welcome the females and diligently gather nesting materials such as stones and straw to build their nests. If they do not build a sturdy nest in a good location, they will not be able to pair with the females, so during this period, the males become aggressive in order to protect their nests from other males.

However, when they are reunited with a female, their behavior changes completely. The individual that previously chased away other males now enthusiastically courts the female and shows no signs of aggression whatsoever. Moreover, they may even accept multiple females. This behavior clearly shows that penguins can distinguish between males and females.

Some males are unable to build their own nests. When such males try to take over a nest, the male who owns the nest will attack and drive them away. Also, if multiple females gather in one nest, they will start fighting to drive out the other females. Conflicts only occur between males or between females.
Seeing this behavior, I really feel that penguins can distinguish between males and females at a glance.

Discovering things not written in books is a unique advantage of visiting an aquarium where animals are kept. Unfortunately, Southern Rockhopper Penguin are currently in a restricted area for breeding and to escape the heat, so you cannot see them. However, there are many other fascinating creatures in the aquarium. Please take your time to observe them carefully. You are sure to make new discoveries.

[Tokyo Sea Life Park]

(June 1, 2018)