African Penguins & Cooperative Feeding
African penguins are sometimes seen feeding at sea cooperatively on so called “bait fish”. Such bait fish include anchovies, sardines (pilchards), redeye round herring, saury and horse mackerel (maasbanker). They form large schools near the ocean’s surface while feeding on plankton. This schooling behaviour has evolved as a means of protection (the more you are in a school the less chance you have of being eaten!). They are preyed upon by top marine predators like sharks, seals, game fish, marine birds, penguins, dolphins and whales and the shape of the ball will change depending on what animal is hunting them.
The penguin’s chief food source in Algoa Bay according to Lorien’s diet sample analyses is definitely anchovies, probably because they have the highest energy content of all bait fish. Most penguins observed at sea are foraging alone or in small groups, but sometimes, when conditions are appropriate, we can see cooperative feeding. We are still unsure about what constitute appropriate conditions: is it water clarity, or behavior of the fish or other reasons? We have observed these penguin bait balls at all times of the year but usually when the water is fairly clear. Photographs taken after the bait ball has finished shows that up to at least 176 penguins are involved at the same time.
What sets this whole process in motion? Usually when a penguin finds some feeding bait fish and starts attacking the fish, a number of events are set into motion. Frightened fish that are being attacked emit a unique odor and intensify their swimming patterns which together attract even more penguins from the nearby scene, as well as other predators. The penguins surround the fish swimming in ever tightening clockwise circles (we are not sure why this is so but it is always clockwise! And we don’t know if penguins from the northern hemisphere would turn anti-clockwise, as there are no penguins in the northern hemisphere!!). This way the fish are forced too close together, which turns their normally synchronic way of swimming in absolute chaos. Also, it is thought that the black and white coloration of penguins helps to confuse the fish (as well as making them less seen by predators while feeding).
Now, this is what the penguins have been waiting for and they just pick off the panicked fish on the outside of the ball with ease. While some are feeding and keeping the ball in place others head for the surface in order to renew their air supply and then return to give the others a chance. Penguins grab the fish head first and their specially modified bills kill instantly. The slippery fish is then swallowed head first and helped down the throat with modified backward pointing barbs. The fish are pinned against the surface and are picked off so that the whole school may be consumed.
Up to 11 other species of seabirds have been observed feeding on penguin bait balls once they reach the surface. Therefore it seems that penguins can play a major ecological role in making this otherwise unobtainable food source available to others. Of course every now and again a Bryde’s whale will come charging in and gobble up the remains of the bait ball much to the disgust of the hard working penguins! Small groups of fish may escape the carnage and continue their life cycles in the pelagic waters.