Watch out birds: The fish are taking their revenge.
At the Schroda Dam in South Africa, scientists have for the first time documented African tiger fish shooting up out of the water to snack on barn swallows. Gordon O'Brien and his colleagues from North-West University captured the sneak attack on film (check out the video on Nature's site), and published their account of the unusual behavior in the Journal of Fish Biology.
Anecdotes of large, bird-eating fish have been circulating since the 1940s. But O'Brien and his colleagues are the first to observe the continuous assault of fins on feathers in a freshwater environment. Tiger fish were introduced to the lake at the Schroda Dam as part of a conservation effort in 2003. The species typically feeds on other fish and crustaceans. At some point, they developed a taste for the swallows that skim over the water.
The researchers counted 300 casualties in 15 days. The more successful hunts took place in deeper water, where the fish were able to launch surprise aerial attacks. Doing so requires the fish to track the exact position of the birds without being misled by distortions from the water. Other carnivorous species, like the archer fish, also share this ability.
The fact that tiger fish are expanding their palate might indicate that their primary food sources are in decline. Since stalking can be dangerous for the tiger fish—at the surface they're easier targets for eagles—O'Brien's team posits that the fish are responding to a pressure severe enough to cause them to develop riskier eating habits. Getting to the root of the problem will allow for better conservation of the species across Africa's wetlands.
The reversal of roles isn't unique to Africa. Around the world, another marine "tiger" is also known to dine on birds. Tiger sharks supplement their diets with migratory birds, as discovered by Marcus Drymon and his research team from the Dauphin Island Sea Lab in Alabama. When they checked the stomach contents of the carnivores, which can grow to be 14 feet long, they found that not all of it was locally raised.
Tiger sharks prowl the waters of the Gulf of Mexico, a popular flyway for woodpeckers, tanagers, swallows, and other birds that overwinter in South America. The American Bird Conservancy, citing a federal study from 2005, says that bright lights from the 6,000 oil and gas rigs in the Gulf cause these birds to fly off-course. Disoriented and travel-weary, they either crash or land on the platforms and quickly become sitting ducks to the indiscriminate sharks. The lights-shark double whammy could be responsible for hundreds, or thousands, of migratory bird deaths, according to the conservancy.
As for the barn swallows in Africa, who knows? Perhaps they'll follow in the wing beats of their cliff swallow cousins in Nebraska, dodging oncoming obstacles—cars or the jaws of a fish—and striving for survival.