Researchers at Dauphin Island Sea Lab in Alabama, who have been conducting a two year study focusing on the diets of Tiger Sharks in the Gulf of Mexico, have made a surprising discovery: not only are the sharks feeding on fish and other marine organisms, they are also feeding on land-based birds, such as woodpeckers, tanagers, meadowlarks, catbirds, kingbirds, and swallows.
“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,” said lead researcher Dr. Marcus Drymon.
The study findings may lend support to an issue American Bird Conservancy (ABC – the nation’s leading bird conservation organization) has been raising for several years, and which was referenced in a 2005 federal government study Interactions Between Migrating Birds and Offshore Oil and Gas Platforms in the Northern Gulf of Mexico. That study made reference to a bird migration phenomenon in which potentially large numbers of night-migrating birds become fatally attracted to lighted oil and gas platforms.
These avian fatal attractions occur more often on cloudy nights, and can involve hundreds or even thousands of birds that apparently confuse the platform lights with stars by which they navigate. The birds become trapped in a cone of light – either reluctant or unable to leave it and fly into a wall of darkness.
“Some birds circle in confusion before crashing into the platform or falling from the sky, exhausted. Others land on the platform where there is no food or drinking water. Some of these birds continue on quickly, but many stay for hours or even days. When finally able to leave, they can be in a weakened state and unable to make landfall, and ultimately, are more vulnerable to predation,” said Dr. Christine Sheppard, Bird Collisions Campaign Manager for ABC.
Studies have shown that hundreds of thousands of birds die from oil and gas platform lighting effects in the Gulf every year. A study often cited is a 2007 report by F.J.T. Van De Laar, Green Light to Birds – An Investigation into the Effect of Bird-Friendly Lighting, which looked at oil and gas platform lighting impacts to birds in the North Sea. The paper suggested that the key to solving the problem lies in the use alternative lights using specific wavelengths. Using green lighting at platforms – as opposed to red or white lights – would nearly eliminate the circling behavior, the study suggested.
Another study, titled Green Light for Nocturnally Migrating Birds and published in Ecology and Society Journal in 2008, showed similar findings – “…..strongest bird responses were found in white light, which seems to interfere with visual orientation ………. the artificial light becomes a strong false orientation cue and birds can get trapped by the beam. ………The bird responses observed in the colored-light conditions are similar to those of previous studies in the laboratory where red light caused disorientation……… it was found that green light caused no or minor disturbance of orientation.”
However, a solution is far from clear as other studies have produced findings that suggest the issue may be more complex. Some studies have also indicated bird attraction could be mitigated greatly by cycling lighting off and on but observed that optimum cycling rhythms have yet to be determined. Studies of cell towers show that strobing white and red lights are far less dangerous than steady burning ones. A simple application of this strategy has been used for the 9/11 memorial in lights, turned on each year on the anniversary of the attacks on the Twin Towers of the World Trade Center. They are monitored and briefly turned off when too many birds accumulate in the beams.
“Some countries, such as the Netherlands, have already instituted bird friendly lighting on oil and gas platforms off their coast. The 2005 study for the Department of the Interior called for research on the issue, but no further action was taken until ABC, in an attempt to advance a solution, requested it. A federal study is now planned for 2013,” Sheppard said.
There are approximately 6,000 oil and gas platforms in the Gulf of Mexico.
This article was written by American Bird Conservancy (ABC), a a 501(c)(3) not-for-profit membership organization whose mission is to conserve native birds and their habitats throughout the Americas. ABC acts by safeguarding the rarest species, conserving and restoring habitats, and reducing threats, while building capacity in the bird conservation movement.