Sharks are pretty versatile eaters. They will prey on everything from fish and invertebrates to marine mammals and turtles. A shark can even have a touch on one or the other surfer. If they can catch it or catch it and it is made of meat, sharks generally eat it.
A new study that identified the contents of the bellies of baby tiger sharks ( Galeocerdo cuvier ) using DNA analysis has found a food component that no one expected: Landsongbirds.
Yes, like the ones you see in your garden, like pigeons, sparrows and meadow larks.
"Tiger sharks will see a light meal and they grab themselves, but I was surprised to learn that the sharks were eating songbirds – I suppose they would be seabirds," said biologist Kevin Feldheim of the Chicago Field Museum.
"It was one of the coolest projects I've been associated with to tell a story with DNA."
It all began after a small tiger shark off the Mississippi-Alabama coast coughed a few feather plumes ̵
This was a surprise, so a team researcher from Mississippi State University decided to conduct further investigations. How common was it? The easiest way to find out what an animal likes to eat is to look at what is being digested in its stomach, and that's what the team did.
Thereafter, in monthly polls between 2010 and 2018, they have turned a blind eye to other strange shark-stomach contents. They pulled the sharks onto the boat, pumped their stomachs, and released the sharks. What a job, hey. During this time, however, they managed to collect the stomach contents of 105 tiger sharks.
Surely there were a whole series of partially digested songbirds in the stomachs of 41 of these sharks. These were found each year during the study period when the team was collecting stomach contents.
This is where the DNA part comes in, as it can be quite difficult to identify a bird when only half of it is left and it's covered with shark bile.
The bird samples were sent to the field museum where their DNA was sequenced and matched with a DNA database. The results were fascinating.
"None of them were seagulls, pelicans, cormorants or any kind of seabird," said marine fishery ecologist Marcus Drymon of Mississippi State University. "They were all land birds."
not. On. Marine. Bird.
Well, at least not identified. They identified only 11 species of birds clearly positive. These were eight passerine songbirds, two near-passerine land birds, and one waterbird (freshwater, not marine).
So how the hell did the sharks get these land birds? A big clue was when they appeared in the stomach of the sharks.
Do you remember how the polls were monthly? The researchers managed to define a peak season for the sharks, which coincided remarkably well with the season when the birds migrated near the habitat of the sharks.
Any straggler falling into the water is a light harvest.  "The tiger sharks eat songbirds that have difficulty flying over the ocean," said Feldheim. "They are already exhausted during the migration and then get tired or fall into the ocean during a storm."
Seabirds may already live near the sea, so they may be better able to do so. Fall into the sea rather than a land bird, and do not make it easy to hunt on them.
The study is a sobering demonstration of the complex dynamics in nature and how much we do not yet know. Not to mention that even changing small things could have an impact we can not even think about.
This could explain why so many shark populations, after swimming in the sea for hundreds of millions of years, are now in dangerous danger of extinction.
The research was published in Ecology .