How Are Birds Ending Up In Tiger Shark Bellies?

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Weird wildlife news has crossed headlines lately: For the second year in a row, researchers have found bird remains in tiger shark bellies. Researchers from Alabama’s Dauphin Island Sea Lab caught the sharks in the Gulf of Mexico, according to an article appearing in the Alabama’s Press-Register. Among their stomachs' avian contents were migratory species, such as scarlet tanagers, as well as more land-based birds, such as brown thrashers.

The findings beg the question: How in the world did creatures of the sky end up inside denizens of the deep?

A few causes factor in. First, there’s the whole migration aspect. Crossing the Gulf of Mexico is extremely arduous for migratory songbirds, says Melanie Driscoll, director of bird conservation for the Gulf of Mexico and Mississippi Flyway. Some birds that aren’t fit for the journey simply don't make it—and a bird that falls from the air could become food in the water, perhaps for tiger sharks. Second, there’s the possibility that birds that perish (from natural causes or for other reasons) in, say, a marsh, could be swept to sea, again becoming potential sustenance.

But there's another reason birds could become shark bait: 6,000-plus oil and gas platforms litter the Gulf, according to a press release from the American Bird Conservancy, and they pose additional obstacles to feathered flyers already facing natural hurdles. Lighting on these structures, for example, could confuse nocturnal migrants on foggy nights, causing them to circulate until they’re exhausted and, perhaps, drop from the sky into the sea. Birds could also collide with the platforms, knocking themselves into the water.

As Driscoll puts it, “We have effectively created a type of urban sprawl in the Gulf of Mexico—tall structures with bright lights, not concentrated like a city, but strewn across a concentration point for birds using both the Mississippi and the Central Flyways.”

The whole scenario—birds becoming food after exhausting themselves from circling around or crashing into manmade structures—is disturbing, no doubt. But what measureable impact does it have on bird populations? Unfortunately, we don’t know. And solutions to the problem aren’t clear-cut, either. A study in the North Sea that showed that using green lighting was less hazardous to birds has been contradicted by other studies. The take home lesson? We need better science in the Gulf to see what effect these structures are having, says Driscoll.

In 2005, the Bureau of Ocean Energy Management, Regulation, and Enforcement (formerly the Minerals Management Service) published a study indicating that lighting on platforms could trap birds, according to the Press-Register article. “While no follow-up studies on the topic have been published,” John Filostrat, a Bureau of Ocean Energy spokesman, said in the Press-Register piece, “there is a study proposed for 2013 that will potentially address some of the questions related to potential impacts of lighting on offshore oil and gas platforms.” Meanwhile, birds will continue to fly the gauntlet set by nature, and us.