Prior to the mid 1850s armadillo dispersal may have been inhibited by native subsistence hunters, the Rio Grande acting as a physical hindrance, and natural habitat barriers posed by fire-maintained grasslands. European colonists settled south Texas in mass during the latter half of the 19th century and largely removed existing impediments to armadillo range expansion, effectively releasing the species into the United States. The speed of the armadillo's natural range expansion after 1850 was probably accelerated by human travel and commerce into and out of its historic range in south Texas on a proliferation of roadways and railroads. This translocation process will likely continue and, combined with natural dispersal, will provide the armadillo the opportunity to ultimately become established in any habitats in the United States in which it can survive. Limits to future distribution will likely be determined by climatic factors, and may be bounded by regions receiving at least 38 cm annual precipitation and having mean January temperatures >-2°C, or fewer than 24 total annual freeze days. Armadillos may have already approached a precipitation-defined boundary to the west and a distribution on the Great Plains limited by winter temperature minima. They may be expected to continue their advance up the East Coast to about the region of 41° North Latitude, decreasing to 39° North Latitude across the midwestern states. Future introductions on the West Coast may result in the establishment of armadillo populations in suitable habitats from California to Washington, an event that has already taken place with another tropical mammal emigrant, the opossum.
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