Exotic Antics

Visitors to Padre Island National Seashore in South Texas who are interested in spotting wildlife are in for a treat. The park is home to an incredible variety of animals, including five species of sea turtles, nearly 400 kinds of birds, armadillos, dolphins and the occasional bobcat — as well as very large bluish antelope that originate all the way from India and Pakistan.

The nilgai stand out, and not only because they literally tower above all other Padre Island creatures. Unlike the barrier island’s native denizens, the invasive antelope, which were imported decades ago for hunting purposes and apparently escaped from nearby ranches, are not welcome in the park. They consume large amounts of grasses, forbs and woody plants, and risk damaging the park’s fragile coastal ecosystem and outcompeting some of the seashore’s residents.

“Life is hard on a barrier island, and the biggest threat the nilgai pose is the direct competition for food resources with our native white-tailed deer populations,” said Charles Sassine, a biological science technician at Padre Island.

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To remedy the situation, the National Park Service is proposing a plan, which it released for public comment in the fall, to eradicate the park’s exotic species including nilgai and feral pigs. The goal would be to protect wildlife habitats and archaeological sites, as well as prevent these species from potentially injuring visitors. (Feral hogs, which have also caused problems at other coastal parks such as Cumberland Island and Canaveral national seashores, are of great concern partly because they like to feast on turtle eggs.) Park managers’ preferred option, which would use existing funding from the Inflation Reduction Act, includes baiting, trapping, ground and aerial shooting, and possible fencing. Palo Alto Battlefield National Historical Park, south of Padre Island in Brownsville, is also plagued by a nilgai invasion, and the park is considering putting out its own management plan once Padre Island’s has been finalized, said Emily Smithey, Palo Alto’s integrated resources program manager.

For all the impact nilgai have on Padre Island, they are even more destructive at Palo Alto. Both parks count upward of 50 nilgai, but Palo Alto’s population seems to be increasing, and because that park is much smaller, the damage there is magnified. “If you go to Palo Alto, there’s piles of nilgai dung everywhere,” Sassine said. “It’s like a big litter box.”

Male nilgai, known as blue bulls in their native range for the gray-blue hue of their fur, can be 5 feet tall at the shoulder and weigh more than 600 pounds. The antelope is the biggest in Asia. “It’s like a deer on steroids,” Smithey said. “They’re just really muscular looking.” They are among the largest invasive animals in the National Park System, according to Jennifer Sieracki, an invasive animals ecologist for the Park Service. Tigers prey on nilgai in their Asian habitat, but Texas predators aren’t big enough to take down such large antelope. (By some unverified accounts, there could be more tigers in Texas zoos, sanctuaries and private homes than there are wild tigers in Asia, but no tiger is known to roam South Texas.)

The nilgai arrived in Texas in the 1920s when the King Ranch, a sprawling estate in South Texas, acquired a few individuals, mainly from the San Diego Zoo. That herd grew quickly, and other ranches built their own. Today, nilgai make for prized hunting trophies, and the King Ranch charges hunters between $2,400 and $5,250 for a nilgai kill. Also, the meat is excellent, said Sassine, who tried it unknowingly. “I thought it was regular beef fajitas,” he said.

There may be as many as 36,000 nilgai in South Texas, and about half reside on a parcel of the King Ranch that sits across from Padre Island. Between the two is the Laguna Madre, a hypersaline lagoon. Sassine said ranch managers didn’t build a fence on the lagoon side because they didn’t think nilgai would swim across — but some possibly did, as early as 2012. (King Ranch representatives didn’t return calls seeking comment.) Barbed-wire fences do separate Palo Alto from ranches adjacent to the park, but nilgai don’t seem to care. “Occasionally, they will take out a whole section, and then the cattle from the neighboring ranches end up on our property,” Smithey said.

The presence of nilgai at Palo Alto was noted decades ago, and park managers suspect numbers have been increasing of late perhaps in part because the antelope realized they’d be safe from hunters within the confines of the park. A few years ago, park staff worked with partners to set up nearly two dozen camera traps and found that an estimated 58 nilgai used the park year-round. While nilgai sightings are rare at Padre Island, they are less so at Palo Alto. “You can look out from our overlook and, on occasion, see them running in a herd,” Smithey said.

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In parts of the park away from visitors, nilgai defecate in what scientists call communal latrines, a behavior that might serve some communication purpose, such as signaling their reproductive availability to potential mating partners. They also produce smaller dung piles pretty much everywhere else, from wide-open prairies to hard-to-reach spots tucked under very thick brush. “And you’re just like, these are big animals. How are they getting into this tight space?” Smithey said. “But they do somehow.”

Maintenance crews remove unsightly mounds quickly, but the damage is not only visual, Smithey said. Nilgai prefer to munch on non-native grasses, and they spread seeds wherever they deposit waste. This dispersion of non-native seeds hinders the park’s efforts to restore native meadows, which the Texas tortoise and other native species depend on. In addition, nilgai, which are members of the bovid family, tend to follow the same paths over and over. “You can just see an endless amount of social trails that they’re creating throughout all of the landscape,” Smithey said.

Nilgai pose problems beyond park boundaries, too. By now, they have established breeding populations outside ranches in South Texas and northern Mexico, and while that pleases hunters, it worries cattle farmers. Nilgai are potential carriers of cattle fever, a disease eradicated in the U.S. but still present in Mexico. Nilgai roam widely and could make outbreaks more difficult to contain. (In parts of their native range, nilgai have been classified as “vermin” for the damage they cause to crops.)

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Nilgai have adapted well to South Texas’ inland plains and brush, but they can’t thrive in Padre Island’s coastal environment, Sassine said. So removing them might be a service to both the park and the nilgai themselves. Recently, two emaciated young females, one of them limping, were seen by a fenced-off pond. “They were in bad shape,” Sassine said. “You could see all their bones.” Sassine suspects they were looking for fresh water, a rare commodity on the island. Also, the park’s perennial grasses hold little nutritional value, which is why native species such as white-tailed deer tend to be “small and very lean,” Sassine said.

“These things are gigantic,” Sassine said of the nilgai. “And that’s part of the problem with them trying to live here. They have way too much body mass to be living in such a poor, poor habitat.”