Who’s been sleeping in my cave?

Research reveals porcupines prominent in many South Central Texas caves   

Writer: Paul Schattenberg, 210-859-5752, paschattenberg@ag.tamu.edu

Contacts: Dr. Roel Lopez, 210-277-0292, roel@tamu.edu

Andrea Montalvo, 210-687-8898, aem595@tamu.edu

COLLEGE STATION — Researchers studying the impact of small mammals on cave habitats with endangered invertebrate species got a prickly surprise when they discovered large numbers of porcupines parading in and out of dozens of caves in the San Antonio area.

“Our initial research was to describe the use of caves by meso-mammals, small to mid-sized mammals, in south central Texas that also contain federally listed endangered species,” said Andrea Montalvo, a research assistant with Texas A&M University’s Institute of Renewable Natural Resources, San Antonio.

The institute operates as a unit of Texas A&M AgriLife Research, the Texas A&M AgriLife Extension Service and the College of Agriculture and Life Sciences at Texas A&M University in College Station.

Meso-mammals include raccoons, opossums, skunks and porcupines, Montalvo explained.

Andrea Montalvo, left, and Chris Thibodaux explore a cave in northwest San Antonio. (Courtesy photo)

Andrea Montalvo, left, and Chris Thibodaux explore a cave in the northwest area of San Antonio. (Courtesy photo)

Montalvo has been working with Chris Thibodaux, a cave and karst specialist with the 502nd Civil Engineer Squadron’s Environmental Flight and Natural Resources unit. She said research they have been conducting in northwest San Antonio for the past three years should provide a more complete analysis of cave system dynamics, allowing biologists to better manage area cave resources and habitat.

“A more complete understanding of caves is essential because of their potential impact on the growth and development of a community,” Montalvo said.

“Recently, a $15 million highway expansion project was delayed after the federally endangered Bracken Bat Cave meshweaver spider was detected for the first time in three decades during the construction of a highway underpass. Construction plans were changed to an overpass and, as a result, the cost nearly tripled.”

“There have been other instances of construction or development in the area that have been halted or delayed due to concerns over harming an endangered species,” said Dr. Roel Lopez, San Antonio institute director.

“Research like this, which helps us understand these populations and their habitats, is vital in understanding and mitigating potential impacts that may arise.”

To conduct their research, Montalvo and Thibodaux set up trail video cameras near 30 cave entrances in northwest San Antonio for one year. Cameras also were placed throughout the tunnels and chambers of caves used regularly by meso-mammals.

“Meso-mammal species, time of day, temperature and total time elapsed were noted,” Montalvo said. “Then the data was analyzed to determine which variables, including cave characteristics, were associated with greater meso-mammal cave use. This data will be used to more fully understand local cave use, allow for more informed management decisions and provide a baseline from which to compare future meso-mammal use.”

While she expected to see meso-mammals such as raccoons, opossums and skunks using the caves, she was surprised by the number of porcupines, Montalvo said.

“Porcupines are relatively rare to south central Texas and they are also typically tree-dwellers, so I was really surprised to find that about 60 percent of all meso-mammal activity in the caves was by them. Their activity was more than that of skunks, opossums, raccoons and armadillos. In one particular cave, their scat indicated an extremely high degree of use,” Montalvo said.

She explained scat, or droppings, left by meso-mammals such as porcupines and raccoons “represent significant energy input into the cave environment in the form of food for other species.”

According to existing research, if the energy input to a cave is too small, cave-restricted species may have no resources. If the input is too large, the cave-adapted species may be replaced by more competitive or predatory species.

“I have been going into caves in central Texas for over 30 years,” Thibodaux said. “Thirty years ago, you never saw a porcupine in central Texas, much less a porcupine using a cave in this part of the state. In fact, the first porcupine I ever remember seeing was as road kill in West Texas, probably around 20 years ago.”

He said “porcupines are prolific poopers” and occupy many caves he monitors.

A porcupine tries to enter a covered cave opening in South Central Texas. (Photo courtesy of Andrea Montalvo)

A porcupine attempts to enter a covered cave opening in South Central Texas. (Photo courtesy of Andrea Montalvo)

Montalvo said the large number of porcupines also presented them the opportunity to investigate their movements and behaviors more thoroughly.

“We decided to track recurrent porcupines with GPS collars and consolidate information on the range expansion, cave use and management implications of porcupines in Texas,” she said. “We trapped them and fit them with GPS collars so we could get data that would allow us to better manage porcupine habitat and understand their role in cave dynamics in this area.”

Montalvo said in tracking their whereabouts she was surprised to learn the porcupines tend to use the caves in this area year-round.

“In the midwestern states, porcupines typically use caves during the winter, but the porcupines in south central Texas use them in the summer to escape the heat and in the winter to escape the cold,” she said.

Montalvo also cited the prevalence of shrubs and lack of large natural predators such as mountain lions as reasons for the porcupines’ migration and adaptation to the South Central Texas area.

“We feel the data we are gathering through this research will not only help in determining the impact of meso-mammals on cave-adapted invertebrates, but also provide insight into how landowners with cave or karst features on or near their land might manage habitat for porcupines,” Montalvo said.

In 2014, the San Antonio Express-News reported an increase in the number of porcupine/pet encounters in the Austin area, resulting in at least one dog getting a muzzle full of quills.

“While porcupines are fairly slow and docile, they have tens of thousands of extremely sharp quills on them and can harm dogs or other animals when they get too close and frighten them,” Montalvo said. “So landowners with caves or karst features on or near their property may want to take extra measures to make sure their pets steer clear of those areas.”


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