How do doves and sparrows end up inside baby sharks?

In 2010, scientists were monitoring a shark population on the border between Mississippi and Alabama. They had hoisted a little tiger shark to tag when something strange happened: feathers. An analysis of the DNA revealed that the shark had eaten a brown carpet, a speckled migratory songbird akin to the mocking bird.

Further analysis revealed that it was not just an isolated incident: a significant percentage of the contents of the shark stomach revealed the remains of birds of barnyard and, surprisingly, a single species of water bird. The study, published in the journal Ecology, demonstrates that food webs are more complex than you think and may even offer predictions about shark behavior.

Scientists analyzed the contents of tiger shark stomach from 2010 to 2018 and found remains of birds each year, except in 2014, in 41 of the 105 sharks examined. Nineteen of these sharks were babies. There were 11 species of birds represented: Barn Swallow, Eastern Kingbird, Housewife, Common Gorge, Wren Wren, Steppe Alpine Moutains, Swamp Sparrow, Brown Mockingbird, White-winged Dove, Yellow Stinkpot and Coot d & # 39; America. These are species that bird watchers from the United States look forward to seeing during the annual migration of birds each spring and fall.

You may be wondering how sharks ended up eating these land birds and why there were no seabirds – researchers too. They examined each of the species on eBird, the community science database maintained by Cornell University, where bird watchers observe their observations to determine when birds should move into the Gulf. The moment when the remains of each bird were found coincided almost perfectly with the peak of the bird's fall migration period in the case of all but two species.

As to how the birds ended up in the ocean, it's not clear. Scientists have speculated that unexpected bad weather in the fall could lead many migrants to the ocean, unable to swim and dying; Previous studies have documented evidence of these massive mortality events. This would explain why there are not many seabirds in the remains of sharks: the eaten birds can not get away from the wave, unlike seabirds, which are better able to navigate the conditions ocean.

This is not the first time that remains of birds have been found in the belly of sharks, author of the Auriel Fournier study from Mississippi State University. tweeted. But what is interesting in this study is that it has followed sharks over time, allowing researchers to relate the behavior of sharks to the behavior of birds. They noted that fall bird migration occurs at about the same time as the peak number of baby tiger sharks, which are generally not ready to hunt alone. Foraging for dead migratory birds could be an important food source until they become capable predators.

Although this is just one specific example of surprising species interaction, it is another example of the surprising links between species on Earth. I just wish I did not have to think about all those dead birds.