Scientists Pumped Baby Tiger Sharks' Stomachs, and Found They Like to Eat Songbirds

Marcus Drymon tiger shark
Scientists empty the belly of a tiger shark as part of their study. Marcus Drymon

Scientists who emptied the stomachs of baby tiger sharks have found the animals feed on songbirds before they have learned to hunt.

The predators, which can grow up to 14 ft-long, have a varied diet that sees them use their powerful jaws and sharp teeth to chow down on food, from fish and sea snakes to turtles and seabirds.

However, there are a handful of accounts of sharks eating terrestrial birds, according to the authors of the study published in the journal Ecology.

The team was partly inspired to explore this phenomenon after they found a small tiger shark along the Mississippi/Alabama coast which regurgitated feathers from the brown thrasher bird which lives on land, in shrubs and trees.

Between 2010 and 2018, they captured 105 tiger sharks in the Gulf of Mexico, pumped their stomachs, and looked at the contents to see if they could find any remnants of birds. The sharks were then released back into the water, unharmed.

In total, 41 sharks had birds remains in their digestive system across 11 species: the barn swallow, eastern kingbird, house wren, common yellowthroat, marsh wren, eastern meadowlark, swamp sparrow, brown thrasher, white-winged dove, yellow-bellied sapsucker, and the American coot. Scientists didn't find a single marine bird in the sharks' bellies.

Sharks likely targeted these birds during the spring and fall, when more than 2 billion migrate across the Gulf of Mexico to and from the Mississippi and Alabama regions, the authors believe.

As they travel, birds can grow tired and can fall into the ocean. The sea creatures can also attack when birds are affected by unexpected poor weather, which can lead them to the surface of the water where they can't stop and take off again. The fall migration also coincides with the birth of tiger sharks in the north-central Gulf of Mexico.

"We suggest that these weather events, while lethal for the birds, provide unique scavenging opportunities for tiger sharks," the authors wrote.

Kevin Feldheim, study co-author and lab manager at the Field Museum, told Newsweek: "I was very surprised that none of the feathers were from marine birds."

"Two in every five sharks that were caught had bird remains, so scavenging on bird carcasses is probably more common than people think.

"To me, the fact that young-of-the-year tiger sharks scavenge on migratory birds shows they are quite adaptable. There is a reason sharks have been around for over 400 million years!"

Feldheim said one of the limitations of this study was that the team doesn't know how important these birds are as a food source for tiger sharks. "For example, if these bird populations suddenly crashed, would tiger sharks be affected, and if so, how much?"

He hopes the findings will help with efforts to protect tiger sharks. "The more we understand about species in general, the better able we are to conserve them," he said.

"Diet studies like this inform food web models which allow managers to consider the interactions between species and how changes in one may affect changes in another."

"As a geneticist, this was one of the coolest projects I have been associated with using DNA to answer a fascinating life history question!"

Last month, a separate group of scientists looked at the diets of a different species of shark: great whites.

Footage shot from cameras attached to sharks revealed the animals charge through underwater forests to hunt for seals in areas previously thought to be inaccessible to the predators. The findings were published in the journal Biology Letters.