Not-So-Vacant Lots

From birds to trees to rats, post-Katrina New Orleans is a study in “disaster ecology.”

Photo: K Schneider/FlickrA female northern cardinal

New Orleans doesn’t sound the same as it did before Hurricane Katrina hit 10 years ago. Jazz and blues may be ringing out in the French Quarter and throughout the Big Easy again, but if you were to stop and listen to the songs of birds, you might find one tune noticeably absent—that of the northern cardinal

“It was a very popular bird in the city, one that people loved to have in their yard,” says the University of New Orlean’s Peter Yaukey, who has conducted bird surveys in the city since before Katrina. “Their numbers fell precipitously after the storm—they basically disappeared—and now they’re so uncommon in the flood zone that I keep track of individual locations when I come across them.” 

Yaukey’s research is just one of the efforts seeking to understand the hurricane’s long-term ecological effects on NOLA. The storm pounded the Gulf Coast with winds that topped 140 miles per hour, and by the time Katrina left, floods inundated more than 80 percent of New Orleans. The influx of brackish water spread sediment across the landscape and killed huge numbers of trees.

“It’s like when Mount Saint Helens erupted,” says ecologist Michael Blum, head of the Tulane/Xavier Center for Bioenvironmental Research. “It was a massive catastrophe.” The storm’s path of destruction has made New Orleans something of a living laboratory, where scientists are investigating the recovery process—or what Blum calls “disaster ecology.”

While Yaukey’s ecological work has largely focused on birds—mocking birds, mourning doves, and European starlings are all thriving, by the way—Blum’s team has spent the last several years compiling data on less charismatic organisms: trees and rats.

Since 2010, the scientists have been monitoring 500 plots across the city, mapping everything from towering oak trees to grasses just a few inches high. Working with the U.S. Forest Service, they’ve tracked the changing forest canopy in the city and dug up pre-Katrina satellite imagery for comparison’s sake. The research is revealing how vegetation is recovering—important information given the numerous benefits of plants, including the shade and air filtration they can provide. One interesting finding is that the plants colonizing the Lower Ninth Ward, one of the hardest hit areas, are unlike the species that grew there pre-Katrina. The weedy forests that have sprouted up in the numerous vacant lots in the last decade are a mix of plants typically found in more rural areas. Tree cover is also of interest because it’s home to rats.

In the aftermath of Katrina, nobody knew what the distribution of rats was like, or what pathogens the critters might be carrying (and historic records had all been lost due to flooding—“They were in a basement in the Lower Ninth Ward,” says Blum). So four years ago, Blum’s group started studying rats, teaming up with other researchers and local agencies. They trap the rodents, conduct surveys to see if where people think rats live matches up with reality, and perform necropsies to figure out what pathogens the squeakers carry.

Rat trappers in New Orleans in 1914, during an outbreak of bubonic plague.

New Orleans is home to Norway rats and black rats; the latter are infamous (though perhaps falsely accused) for carrying the plague, but Blum says, “they’re actually very sweet.” Norway rats live in underground burrows, while black rats live in tree canopies or the roofs of buildings (the reason they’re also called “roof rats”). 

Every summer and winter, about 10 people don T-shirts that read “Rat Trapping Team” and show a big picture of—you guessed it—a rat. They put out 1,000 to 2,000 traps a week. Rats are neophobic, meaning they don’t like new things. “Getting your hands on an animal is incredibly hard,” says Blum. So the rat catchers use an irresistible bait to entice their quarry: a mixture of tuna, oatmeal, and, peanut butter. “If you’re a rat, it smells wonderful,” he says.

The research has revealed that rats are strongly associated with abandoned and vacant lots. And they carry a host of diseases. Seoul virus, an old-world hantavirus that causes hemorrhagic fever, is rare but present. Rats carrying the bacteria leptospirosis occur across the city, and the team has detected hot spots of another pathogen, bartonella.

“The findings are not a reason to be alarmed, but it is important to know so we can take the right steps to protect health and safety of the public,” says Claudia Riegel, director of the New Orleans Mosquito, Termite and Rodent Control Board, which does extensive trapping as well and coordinates with Blum on the rodent/infectious disease research. “It’s been fabulous—we’re getting a far better picture of what’s going on with roof rats and Norway rats than if we were working alone.”

Back to trees. Blum’s group is investigating whether trees help black rats move throughout the city. By examining satellite imagery, they are trying to get a sense of how the extent tree cover and adjacent buildings may act as rat corridors.

Ultimately, Blum will feed that kind of data into models that will help guide the city’s management decisions. Say, for instance, New Orleans considers clearing out a block of abandoned properties. Blum’s model would forecast how the move might change forest cover and how that, in turn, might affect rodent populations and the spread of infectious disease. “We want to have very detailed information derived from satellite imagery,” he says. “Then we could go block by block and see, if were to take this block out, what would it do to the next block, or six blocks over?”

In the meantime, Blum, Yaukey, and others will continue tracking the progression of NOLA’s wildlife as the city continues to remake itself—and they’re sure to be more surprises. For instance, remember the northern cardinal? Yaukey has found that the one place these conspicuous songbirds are making a comeback in New Orleans is the very place making the slowest recovery: the shattered Lower Ninth Ward. “There’s still so much we don’t understand,” says Yaukey. 


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

Join Us