The last thing a barn swallow probably expects as it’s flying low over a lake is to be met with a mouthful of needle-sharp teeth emerging from the water. And if the bird happens to be flying over a certain lake in South Africa, that may well be the last thing it sees.
A recent study has caught what researchers say are the first scientific observations of a fish launching itself out of the water to catch birds in midair.
Fish preying on birds is not unusual, but it’s not a common part of many fish species’ diets either.
“There are more than 14,000 freshwater fish species in the world,” wrote Nico Smit, director of the unit for environmental sciences and management at North-West University in Potchefstroom, South Africa, in an email. “[But] of those, only about five species are known to prey on birds, so I definitely don’t think it is a widespread behavior.”
For the most part, when fish feed on birds, it’s a meal of opportunity, Smit noted. Either the birds have accidentally fallen into the water, or waterfowl like ducks just happen to paddle over the wrong stretch of a lake or river.
But during a 15 day survey in February 2010, Smit and colleagues saw African tigerfish—which populate a storage lake for the Schroda Dam in South Africa—snatching barn swallows out of the air, they report in a study published online last month in the Journal of Fish Biology.
Unlike other instances of fish eating birds, barn swallows actually seem to be a fairly regular part of a tigerfish’s summer diet when the swallows are available, Smit said. “[The fish] have been incredibly well adapted to hunt the flying birds as part of their daily routine.”
Video taken by study co-author Francois Jacobs, also of North-West University in South Africa, is just getting major media attention now.
Beginning around twilight, tigerfish near the Schroda Dam patrol deep open water near well-vegetated areas. They exhibit a less active lifestyle during the day, which they spend in the deeper, more sheltered water, the study authors write.
But during the 2011 survey, researchers noticed that five of the tigerfish (Hydrocynus vittatus) they had tagged exhibited increases in their midmorning activities.
Smit and colleagues did not observe any of their tagged fish leaping for barn swallows (Hirundo rustica), but they did observe other tigerfish catching the birds in midair.
The fish would either follow the birds in a surface pursuit before leaping up to try and catch them, or the tigerfish would track the swallows from deeper in the water and launch into the air to ambush them.
Smit marvels at the skill it takes for these fish to capture birds on the wing. Tigerfish have to spot a fast-flying swallow from the water, exceed the bird’s speed, compensate for refraction—or the fact that the angle of light changes when it goes from air to water—and then leap out of the water to grab the bird, he explained.
Over the course of their study, researchers saw up to 20 successful attempts on flying barn swallows by tigerfish in one day.
“During the 15-day survey as many as 300 [barn swallows] were preyed upon by the local [tigerfish] population, indicating that this feeding behavior is not occasional,” the study authors write.
They speculate that the scarcity of other food in the Schroda Dam lake, like other species of fish, have driven these tigerfish to attempt loftier prey.
“I think this research also illustrates that we still actually know incredibly little about the behavior of freshwater fish in Africa,” Smit said. “The fact that this amazing behavior has escaped documentation for so long surely means that a lot more needs to be discovered.”
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