Meso-Mammal Cave Use and North American Porcupine Habitat Use in Central Texas

Authors: A. E. Montalvo

Meso-mammals are frequent cave visitors whose role in cave ecology is poorly understood. Understanding meso-mammal cave use is essential because caves are often managed for United States federally endangered, cave-obligate arthropods. My objectives for this study were to quantify annual meso-mammal cave visitation, determine behaviors of meso-mammals while in the caves, to develop multinomial regression to determine which variables best differentiate caves use by each species, and to determine how North American porcupines incorporate caves into their home range and habitat use. North American porcupines (Erethizon dorsatum) were the most common cave visitor (64%), followed by raccoons (Procyon lotor; 14%) and Virginia opossums (Didelphis virginiana; 10%). These results are noteworthy because central Texas caves were historically associated with raccoons and the additional nutrient inputs of North American porcupines could facilitate replacement of cave-obligate species by more competitive, or predatory, terrestrial species. Videos recorded in cave passages showed North American porcupines used caves for denning and grooming, while Virginia opossums used caves for feeding. The strongest multinomial model showed that, compared to North American porcupine, raccoons and Virginia opossums had greater odds of using caves with gates (2.36, 4.10, respectively) and pit entrances (6.11, 2.23, respectively). Conversely, raccoons and Virginia opossums, compared to North American porcupine, had lower odds of using caves that were constructed or excavated (0.42, 0.14, respectively), and visiting during the spring (0.46, 0.28, respectively) and winter (0.43, 0.37, respectively). These variables all likely relate to either Virginia opossums’ and raccoons’ greater dexterity or restricted movements after entering torpor during low temperatures. North American porcupine home range estimates (46–421 ha) and overlap indices (42% and 93%) were larger than expected with females spending a majority of their time near a cave entrance. All individuals selected forested cover at the landscape and point scales. Bare ground was selected at the home range scale likely to be used as trails. The results from my study represent an initial step in understanding meso-mammal cave use in central Texas. Should cave nutrient levels need to be managed, my data can be used to manipulate habitats to make caves less desirable to North American porcupine.

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