|Scientific Name:||Sylvilagus robustus|
|Species Authority:||(Bailey, 1905)|
|Taxonomic Notes:||There are no recognized subspecies of Sylvilagus robustus (Hall 1981). S. robustus was formerly considered a subspecies of S. floridanus (Ruedas 1998).|
|Red List Category & Criteria:||Endangered B1ac(iv); C2b ver 3.1|
|Assessor(s):||Ruedas, L. & Smith, A.T.|
|Reviewer(s):||Boyer, A.F. & Johnston, C.H. (Lagomorph Red List Authority)|
This species is historically known from several mountain ranges, but appears to have been extirpated from three of the four ranges. The Davis Mountains are thought to contain the only extant population of Sylvilagus robustus. The total extent of occurrence in this range is approximately 1,815 km², with a suspected area of occupancy of 730 km² (Ruedas 1998). The species also experiences extreme fluctuations in the number of mature individuals as a result of drought and other threats (Ruedas 1998).
Sylvilagus robustus has historically been known to occur in the Guadalupe Mountains (Texas and New Mexico), the Chisos Mountains (Texas), the Davis Mountains (Texas), and the Sierra de la Madera (Coahuila, Mexico). Currently, it is suspected that the Guadalupe and Chisos Mountains populations have been extirpated (Ruedas 1998). An unconfirmed Sylvilagus population may exist in the Sierra del Carmen, but it is unknown if it is S. robustus (Ruedas 1998).
S. robustus is not known to occur below 1,500 m in elevation, and becomes more common above 1,800 m (Ruedas 1998). The contiguous area in the Davis Mountains that contains suitable vegetation preferred by S. robustus is 1,815 km², but when considering the areas above 1,675 m only, potential habitat within the range is reduced to approximately 730 km² (Ruedas 1998).
Native:United States (New Mexico, Texas)
|Range Map:||Click here to open the map viewer and explore range.|
The population of Sylvilagus robustus in the Guadalupe Mountains has decreased in size continually since it was initially reduced to approximately 50 individuals in the 1940’s (Ruedas 1998). No individuals have been verified from the Chisos or Guadalupe Mountains since the 1960’s (Ruedas 1998). There have been two unconfirmed sightings in the Guadalupe Mountains from the 1970's, but it is probable that both populations have been extirpated (Ruedas 1998). In the Davis Mountains, the only recent specimen that exists is a roadkill from 1997, and that was the first record in 20 years from that area (Ruedas 1998). The population status of the Sierra de la Madera is not known, but it is reported that there may be a population of Sylvilagus in good condition in the Sierra del Carmen, in Coahuila, Mexico, though it is not confirmed to be S. robustus (Ruedas 1998).
S. robustus probably occurred historically in low densities and population numbers, resulting in greater sensitivity to threats and leading to local extinctions (Ruedas 1998).
|Habitat and Ecology:||
Sylvilagus robustus occurs in the mountains in Madrean evergreen woodland (Ruedas 1998).
Little is known about the specific ecology of S. robustus, though it can be assumed that it is similar to S. floridanus, of which S. robustus was formerly a subspecies (Ruedas 1998).
Total length ranges from 37.5-46.3 cm (Cervantes and Lopez-Hernandez 2005).
|Major Threat(s):||The nature of Sylvilagus robustus to occur in small population numbers and densities increases the sensitivity of the species to threats. It is likely that S. robustus is sensitive to drought, as they are observed less frequently in dry years (Ruedas 1998). Habitat destruction, in the form of urbanization, development, cattle grazing, and brush clearing, are reducing the habitat available for S. robustus (Ruedas 1998).|
The Natural Heritage Program in Texas considers Sylvilagus robustus to be rare or uncommon, but no state of federal listing currently exists, largely because of lack of data regarding population status and vulnerability (Ruedas 1998).
Detailed studies are necessary to determine the best approaches to conservation, including studies on population genetics, life history, population status, and the effects of threats (Ruedas 1998), followed by establishment of appropriate management plans and protected areas.
|Citation:||Ruedas, L. & Smith, A.T. 2008. Sylvilagus robustus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 06 March 2015.|
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