Habitat Use and Food Habits of Nutria (Myocastor coypus) in the Rio Grande Village Area of Big Bend National Park
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Nutria are large, semi-aquatic rodents introduced into the United States from South America as a fur resource during the early 1900s. The feeding activities of this invasive exotic species is destructive to wetland habitats and competitive with native species. Nutria first were reported at Rio Grande Village, Big Bend National Park, in 1993. They inhabit the Rio Grande River and adjacent wetlands including the Rio Grande Village (RGV) Beaver Pond, which sustains a population of the endangered Big Bend gambusia (Gambusia gaigei) and the endangered Mexican beaver (Castor canadensis mexicanus). The National Park Service is concerned that nutria and their associated activities may negatively impact these wetland habitats and endangered species. I surveyed the Rio Grande River from Gravel Pit, near Hot Springs, to the mouth of the Boquilla Canyon, including the Beaver Pond and Daniel’s Ranch within RGV for nutria activity sites and possible food sources. I documented and recorded approximately 30 locations of nutria activity along the Rio Grande. I captured, marked, and released 24 nutria. Using the Schnabel and Chapman methods, I estimated that 38-74 nutria inhabit the RGV area. I collected stomach contents from 14 nutria for food habit analysis. To identify and quantify the plant species in the stomach contents, I made reference slides of 19 resident microhistological comparison of plant epidermal tissue and stomach contents. Stomach contents contained common cane (Phragmites australis) (59.86% ), water pennywort (Hydroctyle umbellata) (12.71% ), giant reed (Arundo donax) (6.3% ), spikerush (Eleocharis caribaea) (6.14% ), bermudagrass (Cynodon dactylon) (4.79% ), water hyssop (Bacopa monnieri) (2.0% ), foxtail (Alopecurus sp.) (0.93% ), and flatsedge (Cyperus sp.) (0.71% ). Lineintercept techniques were used to quantify vegetation surveys along the Rio Grande River and at the Beaver Pond. Bermudagrass, salt cedar (Tamarix sp.), baccharis (Baccharis sp.), and Arundo composed the majority of the riparian vegetation. Beaver Pond vegetation was composed primarily of Arundo and Phragmites.
CitationMilholland, M. T. (2005). Habitat use and food habits of nutria (Myocastor coypus) in the Rio Grande Village area of Big Bend National Park (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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