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. (Vestal, 2005)
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. (Schmidly and Davis, 1994; Vestal, 2005)
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. (Chapman and Litvaitis, 2003; Ruedas, 1998; Schmidly and Davis, 1994)
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. (Chapman and Litvaitis, 2003)
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. (Chapman and Litvaitis, 2003)
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. (Chapman and Litvaitis, 2003; Chapman, 1982)
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. (Chapman and Litvaitis, 2003)
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. (Schmidly and Davis, 1994)
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. (Bothma, et al., 1977; Chapman and Litvaitis, 2003)
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. (Lee, 2000)
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. (Chapman and Litvaitis, 2003; Schmidly and Davis, 1994)
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. (Chapman and Litvaitis, 2003)
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. (MacDonald, 2001)
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. (Chapman and Litvaitis, 2003)
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. (MacDonald, 2001; Nowak, 1999; Schmidly and Davis, 1994)
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. (Chapman and Litvaitis, 2003)
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. (Chapman and Litvaitis, 2003)
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. (Chapman and Litvaitis, 2003)
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. (Ruedas and Smith, 2011)
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. (Lee, et al., 2010; Ruedas, 1998; Schmidly and Davis, 1994; Schmidly, 1977; Vestal, 2005)
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.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
an animal that mainly eats the dung of other animals
active at dawn and dusk
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
an animal that mainly eats leaves.
A substance that provides both nutrients and energy to a living thing.
An animal that eats mainly plants or parts of plants.
ovulation is stimulated by the act of copulation (does not occur spontaneously)
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
specialized for leaping or bounding locomotion; jumps or hops.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
scrub forests develop in areas that experience dry seasons.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
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