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Some toothy tigerfish have been documented catching unlikely prey in the most unlikely of ways: snatching birds right out of the sky.

Hosted by: Stefan Chin

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Sources:
https://www.tandfonline.com/doi/abs/10.1080/02705060.2005.9664809
https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.2728
https://onlinelibrary.wiley.com/doi/full/10.1111/jfb.12278
https://www.fws.gov/fisheries/ANS/erss/uncertainrisk/ERSS-Hydrocynus-vittatus_Final_June2019.pdf

Image Sources:
https://commons.wikimedia.org/wiki/File:Hydrocynus_vittatus_The_fishes_of_the_Nile_(Pl._XVII)_(6961607491).jpg
https://commons.wikimedia.org/wiki/File:Chasse_de_pigeons_par_des_Silures_(vid%C3%A9o).webm
Cucherousset J, Boulêtreau S, Azémar F, Compin A, Guillaume M, Santoul F (2012) “Freshwater Killer Whales”: Beaching Behavior of an Alien Fish to Hunt Land Birds. PLoS ONE 7(12): e50840. https://doi.org/10.1371/journal.pone.0050840
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Go to Brilliant.org/SciShow to learn  how you can take your STEM skills to the next level this year! [♪ INTRO]. Lots of fish have been documented  eating birds, from bass to tiger sharks.

But usually it happens in a kinda accidental way that doesn’t require much effort from the fish. Like, some fish might snag a  bird that’s sitting on a reed just above the surface. And even those sharks are just  snacking on songbirds that get worn out during their migration over the Gulf of Mexico.

But overall, the only way most  fish are going to eat a bird is if it comes to them. Not tigerfish. In a 2013 paper, researchers  documented these huge, toothy fish leaping from the water to  catch swallows in mid-flight in a lake in South Africa.

Which isn’t something fish  are generally adapted to do, but the researchers documented  two different tactics they used to go after their feathery prey. Some of the time the fish just went for it, lunging directly at a bird from deep water. Other times they chased along after a  bird from just under the water’s surface -- before leaping out after it.

The chasing method was the  less successful of the two. The researchers believe that’s  because fish had to compensate for the way their view of the  birds was distorted by the water -- and some were better at it than others. When light passes from air into  water, it gets bent, or refracted.

That makes objects appear  distorted, and shifted slightly compared to where they actually are. If you’ve ever noticed how a drinking  straw appears to make a zigzag at the surface of a glass of water,  you know what bird-hunting fish have to contend with. The researchers observed that  the fish who couldn’t compensate went for the less successful  surface-pursuit strategy.

But the fish that were better at  taking refraction into account and adjusting their aim  accordingly, were able to use the more successful lunging-from-the-deep tactic. And we’re not just talking  about an occasional snack. During the 15-day study, these  tigerfish ate 300 swallows.

But why? Effective though they  are, tigerfish aren’t evolved to be natural predators of swallows. Normally, they prey on other, smaller fish.

However, the lake they live in  is artificial, created by a dam. It doesn’t have a lot of  those prey fish living in it. In fact, these particular  tigerfish have to spend as much as three times as much time foraging  for food as their cousins in other habitats.

So, supplementing their diet  with passing birds might be one way they’re adapting to this situation! But it has its downsides, too --  the researchers who did the study think that leaping into the air  after swallows could be exposing the tigerfish to predation  by other birds, like eagles. They’re hoping that other  scientists will continue to study this unique ecological interaction  to make sure it isn’t putting either the tigerfish population  or the swallow population at risk.

But either way, it sounds like small  birds in South Africa should probably be keeping an extra-close eye out  whenever they have to fly over water! Now it turns out these fish had to  solve a physics problem -- figuring out how the bending of light was making  it harder to target their prey. Maybe they should have signed up for  Brilliant’s Waves and Light course.

They would have learned all about how  light and other kinds of waves travel -- and maybe snagged a meal a little easier. All of Brilliant's courses have  storytelling, code-writing, and interactive problems. You can go to brilliant.org/scishow  to learn more -- and score 20% off an annual premium subscription! [♪ OUTRO].