Sharks are fairly eclectic eaters. They’re going to go for prey starting from fish and invertebrates to sea mammals and turtles. A shark might also have a chomp on the odd surfer. If they’ll catch it, or scavenge it, and it is made from meat, sharks will typically eat it.
A brand new examine figuring out the contents of the bellies of child tiger sharks (Galeocerdo cuvier) utilizing DNA evaluation has discovered a dietary part nobody anticipated, although: land-based songbirds.
Sure, like those you see in your yard, similar to doves, sparrows and meadowlarks.
“Tiger sharks will see a simple meal and snatch it up, however I used to be shocked to study that the sharks had been consuming songbirds – I assumed that they’d be seabirds,” stated biologist Kevin Feldheim of the Chicago Area Museum.
“It was one of many coolest tasks I have been related to utilizing DNA to inform a narrative.”
It began after a small tiger shark off the Mississippi-Alabama coast coughed up some land-bird feathers – from a brown thrasher (Toxostoma rufum) throughout a shark inhabitants monitoring survey in 2010.
This was a shock, so a crew of researchers from Mississippi State College determined to analyze additional. Simply how widespread was it? The best approach to determine what an animal likes to eat is to take a look at what’s being digested in its stomach, so that is what the crew did.
Thereafter, throughout month-to-month surveys between 2010 and 2018, they saved an eye fixed out for different unusual shark abdomen contents. They might haul the sharks onto the boat, pump their stomachs, and let the sharks go once more. What a job, hey. However they managed to gather the abdomen contents from 105 tiger sharks in that point.
Certain sufficient, there within the stomachs of 41 of these sharks had been a complete bunch of partially digested songbirds. These had been discovered yearly through the examine interval when the crew collected abdomen contents.
That is additionally the place the DNA half is available in, as a result of it may be fairly laborious to determine a hen when solely half of it stays, and it is coated in shark bile.
The hen samples had been despatched to the Area Museum, the place their DNA was sequenced and matched in opposition to a DNA database. The outcomes had been fascinating.
“None of them had been seagulls, pelicans, cormorants, or any sort of marine hen,” stated marine fisheries ecologist Marcus Drymon of Mississippi State College. “They had been all terrestrial birds.”
Not. One. Marine. Hen.
Nicely, not recognized, anyway. They solely made conclusive constructive identifications of 11 species of birds. These had been eight passerine songbirds, two close to passerine land birds and one waterbird (freshwater, not marine).
So how they heck had been the sharks getting these land birds? Nicely, an enormous clue was in once they had been turning up within the sharks’ stomachs.
Bear in mind how the surveys had been month-to-month? The researchers had been capable of outline a peak hen season for the sharks, which coincided remarkably nicely with the time of 12 months the birds can be migrating close to the place the sharks dwell.
Any stragglers that fall into the water are simple pickings.
“The tiger sharks scavenge on songbirds which have hassle flying over the ocean,” Feldheim stated. “Throughout migration, they’re already worn out, after which they get drained or fall into the ocean throughout a storm.”
In the meantime, as a result of seabirds already dwell close to the ocean waters, maybe they’re higher capable of deal with falling into the ocean than a land hen, in flip making them much less simple to prey on.
The examine is a sobering demonstration of the advanced dynamics at play within the pure world and of how a lot we nonetheless do not know, to not point out that even altering small issues may have repercussions we won’t even start to think about.
Which may clarify why so many shark populations, after swimming the ocean for a whole lot of thousands and thousands of years, at the moment are perilously near the brink of extinction.
The analysis has been revealed in Ecology.