Terns and the Start of the “Sardine Run”
By Lloyd Edwards

1. News

Sounds a bit odd I guess, but that is what is happening in Algoa Bay at present. The terns are of course the birds that lead us to these bait balls which are made up of tiny fish. The Easterly winds that blow during this time of the year create the upwelling of nutrients on which phyto (plant) plankton thrives. This is eaten by the zoo (animal) plankton which in turn feeds the many species of bait fish which are now getting to prey size as early juveniles. We have been seeing Common terns feeding on these fish and have managed to get some really cool photos. Guess the images will not attract as many views as dolphins and whales, but it is all very interesting. The “sardine run” is in the making!

While half a million Common terns breed across America and Eurasia, most of our summer visitors come from the countries around the Baltic Sea, namely Northern Germany, Finland and Russia. When I was a teenager, my brother and I put a ring on one that was recovered in Poskov in Russia! Although numbers have decreased in recent years, as many as 100k visit Southern Africa. Although the main season for adults is from October to April, some immature birds remain here year round. They are often seen feeding in large flocks, which lead us to the bait balls. Sometimes they are seen resting on the water in rafts with their tails pointing upright. When they have had enough to eat they will often roost on the nearby islands, especially Brenton Rock.

There are 38 species of terns found throughout the world. They occupy a whole host of habitats from inland to the coast. The Sooty tern is one of the most aerial of all birds and can spend 5 years “on the wing”! Most terns, including our ones, feed by plunge diving. They stoop from a height and use their momentum to break the surface and catch their prey. Unlike Cape gannets that can attain 15 metres from the initial dive, being less streamlined and much smaller, they seldom plunge deeper than a metre.

We generally find them in the presence of foraging African penguins who force them into a ball and closer to the surface. Predatory fish will do the same thing, which is why fisherman will quickly throw out a lure and troll it through the ball. This is one of the tricks to catching bonito and skipjack tuna in Algoa Bay.

Common terns taken with a Nikon D810, ISO 250, 200mm zoom, f/8 and 1/1250th second. I used a slower than normal shutter speed to try and create some movement in the wings.

Fractions of a second prior to plunging into the water. Unlike a Cape gannet whose wings would be tucked tightly against the body, the tern's wings are still open.

The moment of impact, head under while the wings are still in the air.

This one has a tiny fish in it's mouth. Could be anchovy, sardine or red-eye round herring.

Note the African penguin on the left. They are the ones responsible for bringing the fish to the surface and putting them reach of the other avian predators.