Sharks eating land birds in Gulf of Mexico

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Reproduction and feather molt are two of the most energetically demanding aspects of birds’ lives. The breeding season can last five months or longer, and feather molt can take six to 10 weeks. Just finding enough food to stay alive during these stressful times can be a full time job.

Migratory species face additional challenges. Spring and fall migration can take weeks to complete, but migrants also face dangers ranging from aerial predators to severe weather over open weather.

A recent report from the Dauphin Island Sea Lab in Alabama revealed an additional and totally unexpected danger for land birds crossing the Gulf of Mexico. Sharks in Gulf waters eat a surprising number of land birds, everything from swallows and kingbirds to tanagers and catbirds.

Evidence

Feather balls, analogous to fur balls that cats cough up, have been found in shark stomachs during unrelated research. Some of these feather balls are as big as grapefruits.

These findings prompted researcher Dr. Marcus Drymon to wonder, “How do land birds end up in the water as food for sharks? This is certainly not something we expected to see.”

“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,” said Drymon. “We’re going to take a closer look at this over the next year and see if other factors are contributing to these bird deaths.”

Curious

The American Bird Conservancy (abcbirds.org), the nation’s leading bird conservation organization, has been wondering about this for several years. Its interest was piqued by a 2005 federal study titled Interactions Between Migrating Birds and Offshore Oil and Gas Platforms in the Northern Gulf of Mexico.

The study included concern for potentially large numbers of night-migrating birds that might become fatally attracted to illuminated oil and gas platforms.

On cloudy nights during migration, hundreds and sometimes thousands of birds experience a phenomenon called “nocturnal circulation.” Birds confuse platform lights with the stars by which they navigate. The birds become reluctant or unable to escape the lights’ effects. Some fly until exhausted and drop into the water.

In some cases estimates of as many as 100,000 birds have circled a single platform. Other times birds land on the platforms where they may rest for hours or even days. But without food or water, they eventually die when they make a last desperate effort to leave the platform. That’s how land birds get into sea water where sharks happily gobble them up.

Solution

Fortunately there is a simple solution to this problem — change the color of the lights. Similar problems have occurred around the oil platforms in the North Sea.

A 2007 study of the effects of platform lighting in the North Sea found that using green lights rather than white or red lights would virtually eliminate the problem. White and red light seem to have a disorienting or hypnotic effect on migrating birds. They somehow ignore or perhaps cannot see green lights.

Another study in 2008 reported similar findings. White and red lights disrupted birds’ ability to orient; green lights caused minor problems. So switching to green lights on Gulf oil and gas platforms seems a simple solution to a serious problem.

Another possibility that shows promise is cycling lights on and off during migrations. Strobing lights are far less confusing to birds than steady white and red beams. Studies at cell phone towers have revealed that strobing white and red lights create fewer problems than constantly illuminated lights.

In fact, this strategy has been used at anniversary events at 9/11 memorials at the Word Trade Center site. Lights are simply turned off when too many birds become attracted to the lights.

ABC bird collisions campaign manager Dr. Christine Sheppard says, “Some countries, such as the Netherlands, have already instituted bird-friendly lighting on oil and gas platforms off their coasts.”

About time

Though a U.S. Department of Interior study was planned for 2005, nothing materialized. So ABC has requested that the project be revived. A new federal study is now planned for 2013. Since there are about 6,000 oil and gas platforms in the Gulf of Mexico, it’s about time.

About the Author

Scott Shalaway, who holds a Ph.D. in wildlife ecology from Michigan State University, writes from his home in rural West Virginia. A former faculty member at Oklahoma State University and the University of Oklahoma Biological Station, he has been writing a weekly nature column for newspapers and freelancing for magazines since 1986. Send questions and comments to scottshalaway@gmail.com. You can also visit his Web site, http://scottshalaway.googlepages.com. More Stories by Scott Shalaway

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