When fisheries biologist James Drymon noticed feathers in the vomit of a tiger shark, he first assumed they belonged to some unfortunate seabird: a gull, perhaps, or a pelican. But when he and his team genetically sequenced the feathers, the results surprised them: the quills came from a land-based songbird called a brown thrasher. So what was it doing in a tiger shark's stomach in the Gulf of Mexico?
Drymon, a researcher at Mississippi State University's Coastal Research and Extension Center, and his colleagues sorted through the stomach contents of 105 juvenile tiger sharks between 2010 and 2018. Nearly 40 percent had recently feasted on birds that hail from dry land. In all, the scientists counted 11 terrestrial bird species showing up on the sharks' menu. The results were published online in May in Ecology.
Researchers have known since the 1960s that sharks sometimes eat songbirds, “but what was interesting to us was the prevalence” of the behavior, Drymon says. “This is something that happens every year in a high number” of sharks.
Every fall and spring, songbirds undertake dramatic migrations across the Gulf of Mexico. If bad weather comes along, they can be forced to land on the water—which is effectively a death sentence. “The estimate for the number of migrants that die because of storm-related events is in the billions,” Drymon says. He suspects that sharks have long taken advantage of this twice-yearly nutritional bounty raining down from the skies, but scientists have only recently had the genetic tools to confirm this by identifying partially digested feathers.
The results underscore how interconnected marine and terrestrial ecosystems can be, says University of Miami marine ecologist Neil Hammerschlag, who was not involved in the study: “It shows how opportunistic and amazingly generalist these sharks are.”