Tiger sharks feast on songbirds, study shows | Science| In-depth reporting on science and technology | DW | 21.05.2019
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Tiger sharks feast on songbirds, study shows

Tiger sharks are among the most dangerous shark species for humans. But a new study shows that songbirds are far more likely to fall victim to the predators.

When it comes to unprovoked attacks on humans, tiger sharks are in the same class as great whites and bull sharks.

Still, the statistical likelihood of a swimmer, surfer or diver actually getting bitten by one is rather low.

Just over a hundred tiger shark attacks have been recorded since the late 16th century. Less than a third ended fatally. That equates to one deadly attack roughly every 20 years.

Now, a study has shown that songbirds have it far worse.

Read more: Sharks use Israel's coast as a Jacuzzi

Researcher Marcus Drymon pumping the stomach of a juvenile tiger shark (Marcus Drymon)

Marcus Drymon and his team took the samples directly from the stomachs of young sharks

DNA from shark stomachs

To reach this conclusion, a team of reseachers around Marcus Drymond at Mississippi State University caught 105 juvenile sharks by boat in the Gulf of Mexico.

The animals were less than a meter long (three feet), meaning they had not reached adulthood. The scientists pumped the sharks' stomachs and found that 41 of them had bird remains inside, including bones and feathers. After taking the samples, the researchers released the predators back into the water unharmed.

The biologist and his team then extracted genetic information from the stomach contents and, to their surprise, found DNA traces of a large variety of bird species. They included typical land-living sparrows, swallows, pigeons and even woodpeckers, some of which also are migratory birds.

But what surprised the biologists most was that they found no traces of water birds.

"None of them were seagulls, pelicans, cormorants or any kind of marine bird," Dryman said. 

Read more: Divers spot GREAT white shark near Hawaii

Infografik Zugvogelrouten über dem Golf von Mexiko EN

Where do the sharks go bird hunting?

The sharks don't leave the water to go hunting on land, of course. So how do they obtein their prey? It has do with the migratory routes of the birds.

The sharks were in the Gulf of Mexico during the birds' migration season. "In every instance, the timing of the tiger shark eating the bird coincided with the peak sighting for that species of bird off our coast," Drymon explains.

Kevin Feldheim, who works as researcher at Chicago's Field Museum and was a co-author of the study, adds, "The tiger sharks scavange on songbirds that have trouble flying over the ocean ... They're already worn out, and then they get tired or fall into the ocean during a storm." 

Tigerhaie (Marcus Drymon)

The biologists found these feathers in the shark's stomachs, none of which came from marine birds

Birds that can't swim, he suggests, are probably easier for sharks to prey on than marine birds, which can handle themselves better in water.

It is known, however, that adult tiger sharks do also prey on young albatrosses.

"There's a site of Hawaii, where baby albatrosses learn to fly, and adult tiger sharks pick them off," Feldheim says. 

Read more: Hong Kong activists demand end to shark fin soup

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