The tiger sharks that eat woodpeckers and meadowlarks

Fatal attraction of brightly lit gas platforms

January 2012: Tiger sharks' diet has surprised researchers at Dauphin Island Sea Lab in Alabama. The scientists were studying the diets of the sharks in the Gulf of Mexico and found that as well as feeding on the expected fish and other marine creatures, the sharks were also eating 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?' said lead researcher Dr Marcus Drymon.

‘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.'

Birds become trapped in a cone of lightThe study findings may lend support to an issue American Bird Conservancy (ABC) has been raising for several years, that 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 of Mexico every year, but research suggests that using green lighting at platforms - as opposed to red or white lights - would nearly eliminate the circling behaviour, the study suggested.

Netherlands already has bird-friendly lightingSome 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,' said Dr Sheppard.

There are approximately 6,000 oil and gas platforms in the Gulf of Mexico .

http://www.wildlifeextra.com/go/news/shark-diet.html