About Crotalus ornatus Hallowell, 1854
Crotalus ornatus Hallowell, 1854 is a medium-sized rattlesnake. On average, adults of this species reach 76 to 107 cm (30 to 42 in) in length. Most large individuals are usually no longer than 100 cm (39 in), though maximum lengths of 125.0 cm (49.2 in), 125.7 cm (49.5 in), and 129.5 cm (51.0 in) have been documented in published records. Females of this species tend to grow larger than males. Body color ranges across yellows, olive greens, browns, and black. One of its most distinct features, consistent regardless of body color variation, is entirely black tail scales, which aligns with its common name. This rattlesnake often has a black facial mask: a band that crosses the eyes and extends diagonally downward to the corners of the mouth. Like all other rattlesnakes, this species has a keratin rattle at the tip of its tail. A new segment is added to the rattle each time the snake sheds its skin. Because snakes can shed multiple times per year, and the rattle is fragile and easily broken, rattle length cannot accurately indicate a snake's age unless the terminal end button remains intact. This species, commonly called the black-tailed rattlesnake, is distributed across the southwestern United States (Arizona, New Mexico, and west and central Texas), Mexico as far south as Oaxaca, and the Gulf of California islands of San Estéban and Tiburón. Its range reaches a maximum elevation of 2930 m; it has also been recorded at 6900 feet at McDonald Observatory in the Davis Mountains of west Texas. Its official type locality is Fort Webster, Santa Rita del Cobre, Grant County, New Mexico, USA. All rattlesnakes are carnivorous, and this species feeds primarily on rodents, other small mammals, birds, and small reptiles such as small lizards. Its activity patterns change with the seasons. In spring and fall, it is mainly diurnal. In summer, it becomes nocturnal to avoid high summer heat. In winter, it hibernates in abandoned dens originally created by other animals, often sharing these dens with other snake species. Its locomotion adjusts to the surface it is crossing; it actively switches between sidewinding and rectilinear movement. Although it is a capable climber and skilled swimmer, it is primarily a terrestrial species. It inhabits grasslands, desert areas, rocky and mountainous areas, and high-altitude forests. Breeding takes place in spring, when males follow the pheromone trails left by females. Copulation can last for hours and may happen multiple times across several days. After mating, the male typically remains near the female for several days to block other males from mating with her. Females give birth to live young in summer. Newborns only stay with their mother until they disperse on their own, which usually happens within one to two days. Females are thought to breed annually. Litter sizes can reach 10 to 12 young, but average four to six individuals. The average lifespan of this species is 15–20 years.
