The Jackass Penguin (Spheniscus demersus)

"Why is a penguin sitting in the Museum’s showcase of African birds?" some of our visitors wonder. Many associate penguins with Antarctica, and in fact the Antarctic region with the sub Antarctic islands is home to most penguin species.

Nevertheless, some of the smaller species live on South America and Southern Africa’s coasts, among them the Jackass Penguin, whose range reaches up to Northern Namibia and Natal / South Africa. Especially young animals before sexual maturity can roam even further north.

Besides the Jackass Penguin as the only African species, the distribution area of three more penguin species lies in the southern subtropics; all of them are quite small. The Jackass Penguin weighs only up to three kilograms. The larger species are all living further to the South – an example for the so-called Bergmann’s rule, which implicates that a population of animals of the same kind or a kinship, here penguins, are on the average larger in colder climates. The reason for this is the more favorable surface area to volume ratio; the animals lose their body heat via their skin.

Species that conquered tropical coasts have the opposite problem when onshore. They are getting too hot, especially when breeding openly and unprotected on the ground. Therefore, Jackass Penguins dig pits and cavities for breeding whenever possible, and lay their mostly two eggs in the colder season. Nevertheless, the mortality rate among the fledglings is high, not only because of the scorching sun but also because of numerous raptors in the air (birds of prey or gulls) or on land.

On the mainland, the risks are higher; this is the reason for large penguin colonies on islands. Losses are compensated by the high life expectations of the Jackass Penguin. The animals live up to 20 years even in the wild. Regardless, their population decreased massively to currently 20.000 breeding pairs.

There are multiple reasons for this, but all are anthropogenic, e.g. lack of food because of overfishing, contamination of breeding areas by oil or other chemicals, or breeding losses by domestic animals run wild.

As an adaptation to life in the water, all penguins are white on their body front and grey to black on their back. Penguins preferably hunt in the still bright surface waters. With their white body front and black back, they are less visible from below resp. from above; they are spotted later or not at all by their prey as well as by their predators because of this so-called countershading.

On the contrary, the special facial pattern is rather an adaptation for recognisability among the same species. Possibly the typical „face with glasses“ evolved in a time where the Jackass Penguin shared a common habitat with several other penguin species, which today occurs no longer, at least during breeding season.

Both sexes of the Jackass Penguin look alike as occurs in many other monogamous bird species. Differentiating of one sex, mostly of the males, is only relevant in case the animals mate with ever-new partners before breeding season; in this case, the more conspicuous partner is preferred.

Monogamous parents share the burden of raising their young equally. Jackass Penguin fathers and mothers bring in their throats fish to raise their two fledglings. Depending on the availability of food, after two to four months the fledglings are able to hunt independently in the sea.