About Sylvilagus graysoni (J.A.Allen, 1877)
Sylvilagus graysoni, commonly called the Tres Marias cottontail, is a medium-sized cottontail rabbit. Adult body length ranges from 437 to 480 millimeters (17.2 to 18.9 inches), and it has short ears measuring 57 to 64 mm (2.2 to 2.5 inches). It also has a medium-sized skull, ranging 78 to 80 mm (3.1 to 3.1 inches) in length. Its fur is rufous, and lightens in color near the nape and rump. The underside and tail are whitish, and there is a brown patch on the throat. Its skin is recorded as very thin. The skull of this species has a long upper jaw with long incisive foramina, which are ducts in the mouth’s palate. There is a long gap between the incisors and premolars, and the basilar portion of the occipital bone is distinctly narrow. Like the marsh rabbit (S. palustris), it has bony extensions on the back of the brow (the supraorbital margin) that are fused to the rear of the braincase, the part of the skull that surrounds the brain. Like all rabbits and hares, it has a dental formula of 2.0.3.3/1.0.2.3 × 2 = 28: two pairs of upper incisors and one pair of lower incisors, no canines, three upper premolars and two lower premolars per side, and three upper and three lower molars on each side of the jaw. S. graysoni is similar in overall shape to its close relative the Mexican cottontail (S. cunicularius), which lives on mainland Mexico. It shares three key traits with S. cunicularius: a very deep lower jaw, carotid foramina of comparable width, and similarly sized skulls. These shared traits separate both species from the Eastern cottontail (S. floridanus), which has a shallow lower jaw, narrower carotid foramina, and a larger skull. The Tres Marias cottontail can be told apart from the Mexican cottontail by its shorter ears and reddish fur on its sides. Recognized subspecies of S. graysoni differ in size: S. g. badistes is slightly smaller on average than the nominate subspecies S. g. graysoni. Sylvilagus graysoni is endemic to the Islas MarÃas, which belong to the Mexican state of Nayarit. A late 19th century record of the species noted it was abundant on both MarÃa Madre and MarÃa Magdalena, but rarely seen on MarÃa Cleofa. Later surveys found the species on the three northern islands of the archipelago, but not on MarÃa Cleofa. More recent surveys report that S. graysoni lives on all four islands of the archipelago, with the population on San Juanito classified as the subspecies S. g. badistes. Across all the islands it occupies, the species’ total range is less than 500 square kilometers (190 sq mi). It is the only leporid species native to these islands. Its natural habitat is deciduous tropical forest, though the area it occupies on the Islas MarÃas is more arid than corresponding habitats on mainland Mexico. The habitat is dominated by plant species from the genus Bursera, false tamarind, and chupandÃa. On San Juanito, the rabbit does well in areas with dense trees, shrubs, and agaves that grow 3–4 meters (9.8–13.1 ft) tall. It can also move into abandoned farmland across the islands, though it prefers areas with abundant low shrubs. It occurs from sea level up to approximately 350 meters (1,150 ft) in elevation. Due to its island isolation, S. graysoni does not fear humans the way mainland rabbit species do. Individuals on San Juanito are particularly noted for lacking typical escape behavior. Members of this species spend most of the day resting in shallow depressions under bushes, and emerge into open areas after sunset. The Tres Marias cottontail has few documented predators. These include the Tres Marias raccoon, a subspecies of common raccoon, and two raptors: the red-tailed hawk and the crested caracara. Most of the species’ reproductive behavior remains unknown. One research expedition conducted in March 1978 recorded 11 lactating females, and two pregnant females carrying 75-millimeter (3.0 in) embryos. This species has 42 diploid chromosomes, a chromosome count that it shares with the Mexican cottontail, the eastern cottontail, and the desert cottontail (S. audubonii).
