The nilgai antelope is right at home in deep South Texas.
These current residents of the brush country are descendants of the first “blue bulls” from southern Asia that were transplanted on the famed King Ranch in the 1920s and 1930s, and their numbers have steadily grown from a few dozen to tens of thousands in the past century.
Nilgai are distinctive to say the least, with a number of well-known traits and forage habits. Males can tip the scales at more than 600 pounds though they don’t sport the same headgear as other sought-after antelope species. A truly big bull’s horns will only be roughly a foot in length. Nilgai also feature a unique beard that sprouts midway up their throat. Males are dubbed blue bulls due to their blue-gray coat though some younger males may have tinges of brown on them. Cows and calves are light to pale brown.
It’s also known by biologists and land managers that nilgai don’t do well in colder climates — prolonged hard freezes have been known to be detrimental on the South Texas herd, likely due to their tropical nature — but they are hearty animals that can do well across the scrub country. In fact, nilgai are now found from the Baffin Bay area all the way down to the Mexican border. There are currently free-ranging populations in Brooks, Cameron, Hidalgo, Kenedy, Kleberg and Willacy counties, which also are home to some pretty exceptional whitetail hunting.
Hunting Rio Grande Valley Wildlife Management Areas in Texas
The heaviest nilgai concentration occurs south of the Port Mansfield area and down into the Laguna Atascosa National Wildlife Refuge, which today offers drawn hunts for the exotics that feature an unlimited bag limit. Nilgai also are known to cross the Rio Grande between the U.S.-Mexico border.
While their current home range and behaviors are easy to quantify, the overall management of the nilgai population in South Texas has been somewhat of a mystery. They were introduced by Caesar Kleberg of King Ranch lore, but they sort of just took root and slowly expanded their figures without much in-depth study of their nature.
It wasn’t until noted researcher William J. Sheffield looked into nilgai biology more than four decades after they were introduced that we started to know more about Asia’s largest antelope. Sheffield deduced that nilgai are much like other hooved species, exhibiting differing territorial behaviors during different periods of the year. Nilgai segregate into male and female groups except during the breeding season, Sheffield noted in his research. Bulls also do not maintain a fixed territory but defend a space around themselves. Some breeding takes place year-round, but the principal breeding period in Texas is November through March, according to Sheffield. The peak calving period is September through November.
Since the treatise written by Sheffield in the 1970s, not many studies have focused on nilgai despite being a part of the South Texas landscape for nearly a century. However, because the South Texas ecosystem contains culturally and economically important native wildlife and cattle, there arose a need to better understand the position of the nilgai in the ecological network.
As a result, the Caesar Kleberg Wildlife Research Institute in Kingsville and other state and federal collaborators have been studying nilgai for several years to answer questions as it relates to cattle-nilgai interactions, especially centering on cattle fever ticks (CFT).
There is an effort to eradicate CFT from U.S. soil because CFT carry a parasite that causes fever in cattle, a fever that often is fatal. Nilgai are known to carry CFT, thus there became an interest in documenting nilgai movement patterns in order to develop management strategies to contain and effectively eradicate CFT.
One interesting study involved the nilgai on the East Foundation’s El Sauz Ranch in 2015. That research framework included the capture of 30 nilgai — 15 bulls and 15 cows — which were tagged and released back onto the landscape in order for researchers to track and study their movements for a year.
The data in subsequent months showed some interesting trends, including that about half of the antelope remained on the 10,000-acre ranch tract. Among the animals that moved away from the ranch, the distances varied widely — from a single mile to roughly 30 miles away.
The study also focused on other important questions involving nilgai management, including: Do cattle fences act as a barrier to nilgai movement? And do nilgai relocate to new areas after being exposed to helicopter activities?
The research yielded impressive results in terms of both exotic game management as well as the CFT issue.
Nilgai notoriously have little regard for fences. While researchers discovered that nilgai did not perceive cattle fences as a barrier, they did note that cattle fences do act as one when the fences run parallel with highways. Because of that, they noted that fences were useful in formulating CFT management zones.
Nilgai also had large and variable annual home range sizes, researchers noted, but they detected a trend of young females exhibiting large movement during summer months (June-August). Understanding high-risk periods when nilgai may introduce CFT into new areas can assist with CFT monitoring strategies, according to researchers.
The collaboration on research also examined nilgai responses to multiple types of helicopter-based ranch activities that are common in South Texas: cattle gatherings; large mammal surveys; deer captures; nilgai harvest; and nilgai captures. Researchers found that typical ranch management activities such as cattle gatherings and large mammal surveys did not result in the collared nilgai relocating into new areas, which should be an interesting aside for both cattle ranchers and for land managers and biologists.
As you might expect, capturing nilgai to affix collars produced the largest average distance moved relative to the other helicopter-based activities, according to researchers.
Another nilgai management topic that certainly is pertinent is the competition between exotics, cattle and white-tailed deer for local forage sources. Previous researchers investigating nilgai diets concluded that the antelope consumed a large amount of grass, and that nilgai diets overlapped more with cattle than with white-tailed deer.
Researchers examined the diets of all species as part of a recent four-year study in South Texas, with interesting results. It was found that nilgai were flexible foragers, consuming diets similar to deer during drought, with a typical diet composed primarily of forbs and browse. When rainfall was normal or above, nilgai diets were more variable, similar to cattle at some study sites and were composed largely of grass, while remaining similar to deer at other study sites, researchers noted.
Before the research, the general consensus among land managers was that nilgai do not compete with deer for forage, researchers documented. However, their results indicate that during times when forage is limited, nilgai do have the increased potential to compete with deer for browse. Managers who are interested in managing habitat primarily for white-tailed deer would benefit from keeping nilgai numbers low, the findings concluded.
As part of CFT control efforts, there also were multiple nilgai harvests conducted in late spring and early summer in the same area as the initial study. More than 100 adults and juveniles were taken from a helicopter, and later inspected for CFT, with none of the animals being found to be infected with CFT.
Nilgai will continue to be a large part of the South Texas landscape and now that researchers and biologists know more about these exotics, there will be a continued focus on practicing sound scientific methods in management practices for years to come.
Nilgai Antelope: Did You Know?
- The nilgai is the largest antelope that is native to Asia. It can be found all the way from the Himalayas in the north, to the state of Karnataka in the south. Nilgai were introduced to Texas in the first part of the 20th century for recreational purposes.
- Nilgai are considered an exotic by Texas Parks & Wildlife. There are no state bag or possession limits or closed seasons on exotic animals or fowl on private property. Therefore, they may be taken by any means or methods at any time of year. However, a hunting license and landowner permission are required to hunt them.
