Sylvilagus robustus

Geographic Range

Robust cottontails, or Davis Mountain cottontails, occupy mountainous areas in the southern United States and northern Mexico. They are found in the Trans-Pecos region between the Rio Grande River in New Mexico and the East Pecos River in Texas. This region is highly mountainous, containing the Guadalupe, Davis, Chinati, and Chisos Mountain Ranges, which are home to this species. It was previously thought that they had been extirpated from the Chisos Mountains, but populations have been found there between 2007 and 2012 in Big Bend National Park. Some populations are found in the Coahuila Range in Mexico, south of what was once considered their geographic distribution.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Robust cottontails inhabit pinyon-oak-juniper woodland areas in mountain ranges at elevations mostly between 4700 and 8000 feet, though sometimes also at lower elevations. These areas tend to be dry, brushy mountain areas, and these rabbits inhabit dense brush of sumac or mahogany , emerging only toward evening to feed.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• scrub forest scrub forest
• mountains mountains

Physical Description

Robust cottontails are larger than their closest sister species, eastern cottontails . This light gray species of cottontail has large ears and light gray fur on the dorsal portion of its body with darker iron gray rump and black washing. The tail and underparts are white, the shoulders and top of the tail are brownish, and the abdomen is gray. They have several typical features shared by all species of Sylvilagus : large feet and ears, skulls containing a highly fenestrated maxillary bone, as well as supraorbital processes on the frontal bone, and straight cutting edges on the incisors with peglike teeth behind. The dental formula is 2/1, 0/0, 3/2, 3/3. The feet are particularly thickly furred. Cranial morphometrics most distinctly separate S. robustus from its closest relative, S. floridanus . These distinguishing features include: S. robustus possesses 2 distinct mandibular foramina of different size and conformation than S. floridanus ; different shape of the interparietal and alisphenoid bones; lack of a tympanic process in S. robustus ; mental foramena twice as long and located on the dorsal aspect of the mandible in S. robustus , while foramena on S. floridanus are less than one half as long and high and usually located on the labial aspect of the mandible.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Reproduction

The mating system of robust cottontails has not been extensively studied, but it is thought that mating behaviors are similar to other Sylvilagus species. Breeding occurs at higher elevations than eastern cottontails , so may begin later on average. In almost all Sylvilagus species, aggressive male hierarchy systems exist where dominant males are able to obtain more mating opportunities. Dominance is maintained through aggressive interactions among males. Courting behaviors occur among members of Sylvilagus species, including defensive displays mainly at night. There is little additional information available on mating behavior in robust cottontails. Breeding among Sylvilagus species is promiscuous, with males and females each having multiple partners.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Sylvilagus females can produce several litters per year. Like other lagomorphs , they exhibit induced ovulation, in which ovulation does not occur until copulation, causing breeding synchrony. Young are altricial and born in a nest. The number of young per litter varies according to time of year and corresponding temperature, rainfall, and food availability in the habitat and age of the female. In the range of robust cottontails, mean litter sizes of 4 have been reported. A female's first litter size generally ranges from 2.95 to 5.10. Mean litter size in eastern cottontails , the closest sister species, varies from 3.60 to 5.60. Females can produce up to 5 litters per year.

Gestation length information for robust cottontails are not available. However, a strong correlation between latitude and gestation length has been reported for all Sylvilagus species. Populations in southern areas have longer gestation periods while populations in northern areas have shorter gestation periods to support more litters in a shorter period of warm weather. The average gestation period for S. floridanus is 28 days, with a range of 25 to 35 days.

Sexual maturity for both males and females occurs at one year of age. However, juvenile females (under 1 year of age) may participate in breeding in their first summer. Most Sylvilagus young reach reproductive maturity after one year and participate in second year breeding. Some juvenile male reproductive activity has been reported (under 1 year of age), but has been presumed insignificant due to the polygamous breeding pattern of Sylvilagus . More young males may participate in late season breeding during their first year, as decreased libido has been observed among more senior males late in the season in many species of Sylvilagus .

Neonates of eastern cottontails weigh between 35 and 45 grams upon birth. The young open their eyes between day 6 and 7 and weaning is complete by day 15, with the young beginning to venture out of the nest by day 12.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• induced ovulation induced ovulation
• viviparous viviparous

Female robust cottontails are primarily responsible for caring for the young. Before the litter is born, the mother builds a nest, a slanting hole in the ground in a protected area, and lines it with leaves and a layer of her own fur. In Texas, five of these nests averaged 12.5 cm in length, 10.4 cm in width, and 9.1 cm in depth (Bothma and Teer, 1977). Young are born naked, blind, and therefore entirely dependent on their mothers. Mothers care for their young until they are able to leave the nest.

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Robust cottontails live up to 3 years in the wild but have been recorded living up to 8 years in captivity. Predation is the main limit to lifespan of robust cottontails in the wild.

Behavior

Robust cottontail behavior has not been extensively studied because of their recent recognition as a distinct species and the difficulty of locating populations in the wild. Behavior is likely to be very similar to their sister species, eastern cottontails . Eastern cottontails are solitary and congregate only during the mating season, when males often interact aggressively in competition for mates. Cottontail species are predominantly active between dusk and dawn, times at which it is safest to enter open areas and leave their protective brush environment. In areas where predator populations have been reduced by humans, densities can reach 20 rabbits per hectare. In other areas, densities can be as low as 1 individual per hectare. Territory size varies greatly by population and is dependent on available vegetation.

• Key Behaviors
• terricolous
• saltatorial saltatorial
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary
• dominance hierarchies dominance hierarchies

Home Range

Cottontails generally do not maintain territories. Home ranges overlap where there is cover and food availability during the late fall and winter. However, female home ranges do not overlap during the breeding season. Home range sizes vary substantially seasonally and by habitat quality.

Communication and Perception

Little specific information on communication and perception in robust cottontails is available. Mating communication is primarily based on scent and visual displays by males who compete over female mates. Sound plays a less important role in communication for most cottontails than does scent. Scents are secreted from special glands under the chin and in the groin area. Though rarely vocal, cottontails are capable of uttering high pitched squealing noises as a warning when attacked by a predator and they may drum their rear feet loudly as a warning.

• Communication Channels
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Robust cottontails are strictly herbivorous, as are other cottontails . However, the specific plants eaten vary substantially among species depending on local availability. Cottontails feed on a variety of grasses and forbs but, when such vegetation is scarce during the winter, they eat the twigs and bark of shrubs and small trees. Coprophagy, or the reingestion of fecal pellets, has been documented for many species, although it has not been investigated closely in S. robustus . It is likely that soft, so-called “green food” pellets are ingested by S. robustus before they are even dropped, as 60% of these pellets are composed of useful nutrients.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • lignivore
• coprophage coprophage

• Plant Foods
• leaves
• wood, bark, or stems
• flowers

• Other Foods
• dung

Predation

Robust cottontails experience predation by a number of mammalian and avian predators. In general, cottontail species behavioral responses to predation are well documented. They use dense cover to hide from predators and are active in open areas mostly at night. Cottontails also remain still and quiet when under threat by a predator in order to evade detection and are cryptically colored. Little is known about specific predators species of robust cottontails, but they may be preyed on by gray foxes ( Urocyon cinereoargenteus ), bobcats ( Lynx rufus ), golden eagles ( Aquila chrysaetos ), and great horned owls ( Bubo virginianus ), all of which are found in their range.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Robust cottontails play an important role as a food source for their predators, a relationship which has been proposed to keep their populations cyclic and cause them to peak approximately once every ten years. In addition, they play an important role as hosts to a range of parasites, most importantly ticks, a vector for Rickettsia rickettsii . Specific information on parasites of robust cottontails is not available. Other Sylvilagus species are host to a range of ectoparasites, including ticks of the Ixodidae family, fleas of the Pulicidae and Leptopsyllidae families, and warbles of the family Cuterebridae . Endoparasites include the nematodes Obeliscoides , Trichostrongylus , Longistriata , and Trichuris , and the cestodes Mosgovoyia and Taenia .

Economic Importance for Humans: Positive

Robust cottontails are sometimes hunted as game. Although other cottontail species reproduce rapidly, robust cottontail populations may not survive hunting pressure well because of their limited range.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Robust cottontails have caused minor damage to orchard trees in winter and gardens or other agriculturally important crops in summer. Contrary to their close relative, S. floridanus , robust cottontails are not commonly found in residential areas.

• Negative Impacts
• crop pest

Conservation Status

Sylvilagus robustus is listed as Endangered on IUCN’s Red List, though the population trend is unknown. Other organizations do not list robust cottontails as endangered, likely because of its recent recognition as a distinct species. Because of this recent change, little is known about population trends.

Other Comments

Taxonomic history in this group is complicated and contested. Sylvilagus robustus was first described as a distinct species by Nelson in 1909 on the basis of morphological features and lack of apparent intergrades, but was relegated to a subspecies of S. floridanus by Hall and Kelson on the basis of apparent morphological intermediacy of a single specimen. In 1974, Davis’s Mammals of Texas listed S. robustus as a separate species. It was again described as a subspecies by Schmidly (1977) in his Mammals of the Trans-Pecos after his examination of the widely varied S. floridanus throughout Texas and New Mexico, noting the “considerable overlap in external and cranial measurements among examples of S. robustus and S. floridanus specimens” (Vestal, 2005: 3) and the subspecific level differences within S. robustus . In 1994, Schmidly and Davis again updated the classification, noting classes of nominal cranial differences between S. floridanus and S. robustus , which were confirmed by a morphological analysis of 26 cranial, mandibular, and dental characters in 5 taxa of cottontails (Ruedas, 1998). Since that time, S. robustus has been recognized as a distinct species, although a 2005 study by Vestal suggested that subspecific genetic variation in cytochrome b exceeds interspecies divergence between S. robustus and S. f. cognatus . In response and explanation to this study, Lee et al. (2010) amplified fragment length polymorphisms using DNA fingerprinting techniques, which showed that there was a lack of gene flow between the two species and that this, combined with morphological data, should be enough to classify S. robustus as a distinct species.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Stephanie Schuyler (author), Yale University, Eric Sargis (editor), Yale University, Rachel Racicot (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

References

Bothma, J., P. Du, J. Teer. 1977. Reproduction and productivity in South Texas cottontail rabbits. Mammalia , 41/3: 253-281.

Chapman, J., G. Ceballos. 1990. Rabbits, hares, and pikas: status survey and conservation action plan . Gland, Switzerland: IUCN.

Chapman, J., J. Litvaitis. 2003. Eastern Cottontail: Sylvilagus floridanus and allies: Wild Mammals of North America: Biology, Management, and Conservation . Baltimore, MD: Johns Hopkins University Press.

Chapman, J. 1982. Latitude and Gestation Period in New World Rabbits. The American Naturalist , 124/3: 442-445.

Lee, D., R. Pfau, L. Ammerman. 2010. Taxonomic status of the Davis Mountains cottontail, Sylvilagus robustus, revealed by amplified fragment length polymorphism. Journal of Mammalogy , 91/6: 1473-1483.

Lee, E. 2000. "Sylvilagus floridanus" (On-line). Penn State New Kensington Species Page. Accessed April 01, 2012 at http://www.psu.edu/dept/nkbiology/naturetrail/speciespages/cottontail.htm. .

MacDonald, D. 2001. Sylvilagus. Pp. 457-460 in The Oxford Encyclopedia of Mammals , Vol. 1/1, 3rd Edition. London: Oxford University Press.

Nowak, R. 1999. Walker’s Mammals of the World, Sixth ed . Baltimore, MD: Johns Hopkins University Press.

Ruedas, L., A. Smith. 2011. "Sylvilagus robustus" (On-line). IUCN Red List of Threatened Species. Accessed April 01, 2012 at http://www.iucnredlist.org/apps/redlist/details/41310/0. .

Ruedas, L. 1998. Systematics of Sylvilagus Gray (Lagomorpha: Leporidae) from Southwestern North America. Journal of Mammalogy , 79/4: 1355-1378.

Schmidly, D. 1977. Mammals of the Trans-Pecos . College Station, TX: Texas A&M University Press.

Schmidly, D., W. Davis. 1994. The Mammals of Texas . Austin, TX: Texas Park and Wildlife Department.

Smith, A. 2008. Conservation of Endangered Lagomorphs . Heidelberg: Springer Verlag.

Vestal, A. 2005. Genetic Variation in the Davis Mountain Cottontail (Sylvilagus robustus). ProQuest Dissertations and Theses , 1/1: 1-71.