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Every fall and spring peregrine falcons migrate along the shores of South Padre Island on a 5,000-mile journey that takes them from their breeding grounds in the Arctic to South America.

In a joint effort between the Peregrine Fund and Earth Span, researchers have been monitoring the peregrines passage, and the 36-year study is one of the longest continuous field research projects in the world.

Peter Jenny, President and CEO of the Peregrine Fund, said, "This is a wonderful opportunity to study peregrine falcons, as you know at one time that was a critically endangered species.  The good story is that 10 years ago they were delisted; they were removed form the endangered species list.  Now, as scientists we get to use them, because they are a wonderful indicator species of the health of the environment.  Padre Island right here is an incredible part of that story, because this represents one of the best concentration points of peregrine falcons migrating from North America to the wintering grounds in South America."

Researches capture the falcons, weigh and measure them and take blood samples before banding and releasing them.

The banning of the harmful pesticide DDT in 1972 enabled the peregrine falcons to rebound, but now this indicator species faces a possible new threat.

"They are the indicator species, because they live at the end of a very long, very complex food chain, and in each one of those steps they tend to accumulate those toxins.  You know, right now we are concerned about the effects of those oil spills that have happened here in the Gulf, and we have encountered some of the highest concentrations in the blood of these peregrine falcons of any species recorded to date of these PAH's, that's a poly-cyclic aromatic hydrocarbon.  That's just a fancy word for a marker for raw petroleum, and these spills happen naturally," said Jenny.

While researches do not yet know whether these elevated levels are the result of the huge BP spill in March of 2009 or perhaps other sources they will continue to monitor the peregrines on their migratory journey.