Researchers in the Gulf of Mexico conducting a two year study on the feeding habits of tiger sharks (Galeocerdo cuvier) in the gulf have been shocked by what they have found in the stomachs of these apex predators. Birds, and not just of the ocean going kind, but a variety of different land-based species, including catbirds, kingbirds, meadowlarks, swallows, tanagers, and woodpeckers have been found in the stomachs of these opportunistic feeders, according to a press release by the American Bird Conservancy.
Though the scientists say that migratory patterns of land-based birds over the ocean contributes to bird deaths over water, the scientists lend some credence to an issue that the American Bird Conservancy has been vocal about for several years–that of a bird migration phenomenon over the gulf that results in the death of night migrating birds due to lighted oil and gas platforms. The ABC cites a 2005 study by the federal government titled “Interactions Between Migrating Birds and Offshore Oil and Gas Platforms in the Northern Gulf of Mexico.”
According to the study, the fatal bird flights occur when there are more clouds in the sky that obscure the vision of the migratory birds. The scientists speculate that the birds, often flying in flocks of thousands, mistakenly view the lights of oil platforms as the stars that the birds use to navigate the night sky. They become trapped in a cone of light, a sort of tunnel vision, and fly straight into the platforms or circle the platforms and fall into the ocean from exhaustion. This is where the tiger shark comes in. Unlike the great white shark (Carcharodon carcharias), which has more specific food requirements (sea mammals, dead land and ocean animals, large fish, and other sharks) and hunts accordingly, the tiger shark is more of an opportunistic feeder. Known as the garbage can of the sea, the tiger shark feeds on everything from sea turtles to sea birds and dead animals, and now, land-based birds that have lost their way.
“We were not expecting to see this. It certainly prompts a series of questions, the most obvious being, how does a land bird end up in the water as food for sharks? Certainly, bird migrations across the Gulf are incredibly strenuous treks that result in large numbers of bird deaths over water from exhaustion, but there may be other factors at play here. We’re going to be taking a look at this over the next year and see if there are other causative circumstances that are contributing to these bird deaths,” Dr. Marcus Drymon, lead researcher said in a press statement released by the ABC.
Several studies on the impact of lighted oil and gas platforms on bird migration have been made over the years, including a study published in 2007 that suggested changing the lights on the platforms to green from red or white lights would virtually eliminate the circling behavior of birds, and another study published in Ecology and Society Journal in 2008 titled “Green Light for Nocturnally Migrating Birds” surmised that white and red light is a contributing factor to bird disorientation and green light caused minimal or nil disturbance in bird disorientation.