“Tiger sharks will see an easy meal and snatch it up, but I was surprised to learn that the sharks were eating songbirds—I assumed that they’d be seabirds,” co-author Kevin Feldheim of Chicago’s Field Museum said in a statement. “It was one of the coolest projects I’ve been associated with using DNA to tell a story.”
Marcus Drymon of Mississippi State University — lead author of the study published in the journal Ecology — and his colleagues focused on baby tiger sharks and analyzed their diet. Of the 105 sharks they studied, 41 were found with bird remains in their stomachs.
Researchers couldn’t determine what kinds of birds were in their stomachs because they were partially digested, so they sent the bird remains to the Field Museum’s Pritzker Laboratory for Molecular Systematics and Evolution for DNA analysis. They tested the remains using various chemicals and then compared them to those in the database.
“None of them were seagulls, pelicans, cormorants, or any kind of marine bird,” Drymon said. “They were all terrestrial birds”—the kinds that might live in your backyard.
This is not the first record of tiger sharks eating birds. According to Feldheim, there is a site off Hawaii where albatross babies learn how to fly, which is a great opportunity for sharks to grab them. However, this is the first time baby sharks were recorded has having songbirds on their menu.
“The tiger sharks scavenge on songbirds that have trouble flying over the ocean. During migration, they’re already worn out, and then they get tired or fall into the ocean during a storm,” Feldheim explained.
He believes terrestrial birds appear to be more attractive prey because they are not as good at handling themselves over the sea as seabirds.
This study helps scientists get a better understanding of baby tiger sharks and tiger sharks in general. This study especially contributes to improving protection for these predators.
“All sharks are in trouble,” Feldheim said. “We don’t know the extent of how industrialized fishing has taken a toll, but the vast majority of top predator populations have declined in recent years.”
However, scientists note that beyond the conservation and protection of the sharks, this study is important to improve databases about sharks which are currently available to scientists by showing how many more things they can learn from their DNA.