Texas Tech University

DAVIS MOUNTAINS COTTONTAIL
Sylvilagus robustus (V. Bailey 1905)

Order Lagomorpha : Family Leporidae

Description. A large, pale buffy gray species with rather large ears; upperparts pale, dull buffy, washed with blackish; rump iron gray, contrasting with back; nape rufous; top of tail dull brownish; legs rusty; sides of head and abdomen grayish; shoulders brownish; underside of neck grayish or brownish; rest of underparts, including tail, clear white. Averages for external measurements: total length, 416 mm; tail, 53 mm; hind foot, 98 mm; ear from notch, 71 mm. Weight, 1.3–1.8 kg.

Sylvilagus robustus

Distribution. In Texas, restricted to the mountains of the central Trans-Pecos (Guadalupe, Davis, and Chisos). Also known from the Guadalupe Mountains in New Mexico and from the Sierra de la Madera of Coahuila, Mexico.

Distribution of Sylvilagus robustus

SUBSPECIES. Monotypic species.

Habits. The following account is based on the notes of William B. Davis during his fieldwork in the 1940s in the Chisos Mountains.

In the Chisos Mountains these rabbits prefer thickets of sumac, mountain mahogany, white brush (Lippia), and scrub oak as refuge sites. They usually spend the greater part of the day resting in such thickets and emerge late in the evening to feed in the interspersed open areas. On 2 May 1944, Davis flushed five of these rabbits in the basin of the Chisos Mountains. All were encountered in or near the bottoms of ravines where the brush was fairly dense. Three of them were flushed from under the basal rosettes of the large agave (Agave scabra). They often disappeared quickly in the dense brush, although he observed that they rely a good deal on freezing for protection. Their usual tendency is to run a short distance then stop, when they are partly concealed by vegetation, and watch the intruder. They also frequent rocky areas where boulders are large and utilize the associated crevices and crannies as retreats.

They feed most frequently in the late evening and early morning hours but occasionally do so during the hotter part of the day, as evidenced by notebook records of feeding at 10 a.m. and 2 p.m. in May. Their food consists of grasses (at least Muhlenbergia and Bouteloua), leaves of mountain mahogany, white brush, and numerous herbs.

The breeding season apparently is restricted to spring and early summer. A female collected in the Chisos Mountains on 6 April was lactating and had given birth to two young shortly before (determined by uterine scars). Another taken on 16 June was lactating and had borne three young. She was molting extensively on the back, sides, and breast. Several young of the year about the size of a man's fist were observed in June.

Nothing is known about the natural predators of this rabbit, but it is likely that it is preyed on by gray foxes, bobcats, golden eagles, and great horned owls.

Population Status. Uncommon. This species is restricted to the mountains of the central Trans-Pecos (Guadalupe, Davis, and Chisos). It generally occurs only above 1,800 m (5,900 ft.) and is a montane specialist. Although this species may be locally abundant, its elevational requirements prevent a widespread occurrence.

Conservation Status. The IUCN lists this species as endangered, but it does not appear on the USFWS or TPWD lists. Given its restricted distribution (montane regions of Texas, Guadalupe Mountains in New Mexico, and from the Sierra de la Madera of Coahuila, Mexico), this rabbit will almost certainly require conservation efforts in the future.

In 1998, Luis Ruedas (Portland State University) expressed concern that populations of this rabbit have declined dramatically in recent decades. Ruedas recommended state listing for this species, as well as listing as endangered by the IUCN, pending the completion of more detailed studies about the natural history of S. robustus, including assessment of population status and life history parameters, long-term ecological studies, and population genetic analyses. The Guadalupe and Chisos Mountains populations have been severely reduced, and no specimens have been seen or collected from these areas in the past 30 years. Recently, mammalogists from Texas Tech University obtained several specimens from the Davis Mountains, and it appears that a healthy population remains in the area. Careful monitoring of this species is needed throughout the isolated mountain ranges of the Trans-Pecos and northern Mexico to determine its overall conservation status.

Remarks. Throughout his many editions of The Mammals of Texas, William B. Davis continued to recognize S. robustus as a distinct species from S. floridanus. In the 1994 edition, authored by Davis and DJS, however, S. robustus was arranged as a subspecies of S. floridanus on the basis of nominal cranial differences. In a 1998 article published in the Journal of Mammalogy, Luis Ruedas documented distinct differences in size as well as skull and tooth morphology that separated robustus from the various subspecies of floridanus. On that basis, Ruedas proposed that S. robustus is a distinct species. In 2010, Loren Ammerman of Angelo State University and her students, using DNA sequence data, agreed that S. robustus should be recognized as a distinct species.

In the late 1990s, Clyde Jones and RDB at Texas Tech University made an extensive collection of rabbits in the Davis Mountains and recorded robustus-type specimens occurring with floridanus-type individuals. On that basis, and the genetic data, we have chosen to recognize S. robustus as a distinct species. 

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From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016.  Courtesy of the University of Texas Press.

Natural Science Research Laboratory