How are songbirds ending up in tiger shark bellies? New study has some surprising answers
Tiger sharks are notorious for eating almost anything, but an ecologist who studies the fish for a living was still surprised by what happened on a catch-and-release expedition on the Gulf of Mexico in 2010.
A juvenile tiger shark that was wrestled onboard the boat to be measured and tagged threw up on deck. Out came a ball of feathers, Mississippi State University fisheries ecologist Marcus Drymon told National Geographic.
“Being a scientist, of course, I scooped them all up and took them back to the lab to analyze,” Drymon said.
Drymon got help identifying the feathers from Kevin Feldheim, a friend and molecular biologist at The Field Museum in Chicago, according to Popular Science Magazine.
Using a technique called DNA barcoding, Feldheim identified the feathers as that of a brown thrasher — a songbird commonly found in suburban yards.
Intrigued, Drymon decided to investigate the phenomenon.
Over a nine-year study in which they studied the stomach contents of 105 small tiger sharks, Drymon and his team pieced together a theory.
More than 40 of the sharks’ stomachs contained remains of common songbirds such as sparrows, doves, woodpeckers and wrens. All of the species were migratory.
The birds migrate south over the Gulf of Mexico in the fall, traveling over the same coastal waters that tiger shark moms use as nurseries for their newborns.
One of the hazards of the journey is occasional cold fronts, which can send large numbers of birds plummeting into the sea. The fallen fowl make easy pickings for young tiger sharks in search of a meal, the researchers concluded.
“All of the sudden, it’s not just a gee-whiz observation,” Drymon told Popular Science Magazine. “It’s something they do relatively frequently. It was really mind-blowing when we were able to put this together.”
More research is needed to confirm the theory, but it makes a convincing explanation for the unexpected phenomenon.
The study, titled “Tiger sharks eat songbirds: scavenging a windfall of nutrients from the sky,” was published in peer-reviewed science journal “Ecology” on May 21.