The propensity of tiger sharks to eat almost anything they could sink their teeth into seems to start at a very young age.
Scientists in Alabama, Chicago, and Mississippi examined what a normal diet would be for juvenile tiger sharks. They found several items in the animals' bellies, the most interesting of which are body parts of birds.
What is surprising about the discovery is that the birds were not even regular seabirds but species commonly found in home backyards, such as doves, sparrows, and woodpeckers.
"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," said Kevin Feldheim, a researcher from Chicago's Field Museum and one of the authors of the study.
Feldheim was the one who conducted the DNA analysis that identified what kind of birds were found in the sharks' stomachs.
"It was one of the coolest projects I've been associated with using DNA to tell a story," he added.
Backyard Birds In Baby Tiger Sharks' Bellies
Marcus Drymon, a marine fisheries expert from Mississippi State University, led the team in inspecting the stomach contents of 3-foot-long baby sharks. They pumped the animals' bellies and analyzed the different items that were regurgitated. They then released the sharks back into the ocean unharmed.
Of the 105 baby tiger sharks that they examined, 41 of them had bird remains in their bellies. However, since many of the birds' parts have already been partially digested, the researchers had a difficult time identifying what specific species they were.
To solve this problem, the team sent samples of the bird remains to the Pritzker Laboratory for Molecular Systematics and Evolution at the Field Museum for DNA analysis.
After obtaining the samples' DNA sequences, the researchers then compared them to records of bird DNA to determine what specific birds they were from.
They discovered that none of the samples were from species typically found at sea, such as cormorants, pelicans, or seagulls. Instead, they were all from terrestrial birds, the ones that could be found in backyards.
Tiger Sharks' Voracious Appetite
Tiger sharks have gained a reputation in the animal world for having a voracious appetite. They are known to just eat anything that could fit in their mouths, including rubber tires and other man-made wastes.
Some sharks have even been shown to eat birds, such as baby albatrosses in Hawaii still trying to learn how to fly, according to Feldheim.
However, the new study is the first instance where tiger sharks have been observed to eat songbirds that are typically found in the land. This is because these predators often travel to 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 said.
Feldheim explained that the sharks likely scavenged on songbirds that have difficulties making the flight over the ocean. He said these birds are already worn out due to their migration, and they often get tired or fall into the water during storms.
The researchers said the tiger sharks might be more attracted to songbirds than seabirds because these terrestrial birds are less capable of handling themselves in or around bodies of water compared to marine birds.
Drymon and his colleagues hope that their work could lead to better ways to protect tiger sharks, which they believe are in trouble.
It is still unknown just how much-industrialized fishing has affected the animals, but Feldheim said a large number of top predator populations have already dropped in recent years.
He also pointed out how DNA databases can help scientists understand more about sharks.
The findings of the multi-organizational study are featured in the journal Ecology.