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BATON ROUGE -- One of the great wildlife events of the world takes place over the heads of Louisiana residents every spring, says an LSU biologist.
Preliminary estimates from recent research indicate that more than half a billion birds fly over the Gulf of Mexico and enter the United States over the east coast of Texas and all along the Louisiana shoreline each spring, said Bob Russell, a researcher with LSU's Museum of Natural Science.
Russell is one of several scientists tracking bird migration across the Gulf of Mexico. With a $535,000 grant from the Minerals Management Service and matching funds from Exxon, Mobil, British Petroleum, Phillips and Texaco, ornithologists have taken to the offshore oil rigs to observe migration.
This huge migration is largely invisible to people, said Russell, because the birds fly at altitudes of 2,000 to 5,000 feet and because they come in over relatively uninhabited marshland and usually do not stop on the coast. "They proceed inland because their fat stores haven't been depleted completely, so they are capable of doing so. Also, there really aren't a lot of habitats suitable for migratory stopovers on the coast, so they continue on to denser woods," he said.
It takes most birds 11 to 18 hours to cross the roughly 600 miles of the Gulf from the Yucatan, where many of them stage before the crossing. Their high flight gives them the advantage of tailwinds, which may boost their speed up to 40 knots -- a little faster than 46 miles per hour.
Most of the birds winter in Mexico and Central America, but a few come from as far away as South America. The seven full-time observers working offshore have identified about 170 species, most of which fly in small, mixed-species flocks of 25 to 100 birds. After they reach Louisiana, they spread throughout the Eastern United States, some going as far as central Canada.
Most of the time, when the weather conditions on the Yucatan are good, conditions all across the Gulf will be favorable for the migration, Russell said. But occasionally, the winds become adverse and the birds fall out onto the offshore oil platforms where the observers see them.
So far, Russell and his team have studied only the spring migration. Some birds might not take the direct route across the Gulf when heading south in the fall, Russell said. "The ruby-throated hummingbird is an example. It's a trans-Gulf migrant in the spring, but in the fall there are large flights observed on the coast, going around the Gulf. So we really don't know what's going to happen. Our suspicion is that birds that migrate by day go around the Gulf in the fall and those that migrate by night go across the Gulf."
The discovery that large numbers of ruby-throated hummingbirds do fly across the Gulf ends a long-standing controversy. In the early 1950s there was a lot of dispute about the ability of the hummingbird to fly so far. "People did some physiological calculations and said, ëHey, it's absolutely impossible. Ruby-throated hummingbirds can't carry enough fat to fuel trans-Gulf flight.' It's been pretty controversial until now," Russell said.
Something perhaps even more surprising is that several species of dragonflies have been identified as true trans-Gulf migrants, he said. The green darner and spot-winged glider have been identified, but the most famous migratory insect, the monarch butterfly, apparently stays over land.
The migrations are tracked by National Weather Service Doppler radar at the same time the observers are out on the platforms. "The radar gives us a really good picture of where the flights are coming in and how many birds are involved, but it doesn't give us any indication of what species they are," Russell said. That's where human observers come in.
Not all the birds that cross the Gulf fly from the Yucatan. Radar also indicates that some birds seem to be coming in from the Brownsville, Texas, area.
Russell is a post-doctoral researcher with LSU's Museum of Natural Science who holds degrees in mathematics ecology and has a passion for birds. He came to LSU from the state of Washington especially for this project. Other researchers include LSU Museum of Natural Science curator Van Remsen; museum research associate Donald Norman, who will compare tissue contaminants in birds flying north in the spring with those flying south in the fall; and Sidney Gauthreaux, who received his doctorate at LSU and is now on the faculty at Clemson. Gauthreaux, a pioneer in the study of trans-Gulf migrations, is doing the radar work.
The researchers will go back offshore from August through October. The project ends with the spring migration of the year 2000.
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