Tiger rattler, Tiger rattlesnake
The tiger rattlesnake (Crotalus tigris ) is a highly venomous pit viper species found in the southwestern United States and northwestern Mexico. No subspecies are currently recognized. The specific name tigris, Latin for "tiger", refers to the many narrow dorsal crossbands, which create a pattern of vertical stripes when viewed from the side.
The Tiger rattlesnake is a highly venomous pit viper species that is easily identified by its small, spade-shaped head. It has the smallest head of any rattlesnake and a large rattle. The color pattern consists of a gray, lavender, blue-gray, pink, or buff ground color that usually turns to pink, pale orange, or cream on the sides. Tiger rattlesnakes are the only rattlesnake with crossbands on the anterior portion of their bodies, with a series of 35 to 52 gray, olive, or brown bands across the dorsum consisting mainly of heavy punctations. These crossbands have vague borders and are wider dorsally than laterally. The most distinguishable mark on the head is a dark cheek strip.
Tiger rattlesnakes are found in the southwestern United States and northwestern Mexico. They occur from central Arizona south through south-central Arizona in the United States, to southern Sonora, Mexico, including Isla Tiburón in the Gulf of California and was recently discovered in the southern Peloncillo Mountains of Arizona. Tiger rattlesnakes inhabit rocky desert canyons, foothills, and bajadas, in vegetation zones ranging from thorn scrub, ocotillo-mesquite-creosote bush, saguaro-paloverde, mesquite grassland, and chaparral to tropical deciduous forest (southern Sonora) and the lower edge of oak woodland. In southeastern Arizona, these snakes occur strictly in rocky areas in winter and spring but use edges of arroyos in summer.
Tiger rattlesnakes are solitary and prefer to spend their time singly. They are nocturnal during the hot summer (June-August) but become diurnal and crepuscular during the fall season. They hibernate during the late fall and winter in rock crevices or animal burrows. In spite of being ground-dwelling, their activity is not restricted to the ground. They swim readily and have been found in bushes 60 cm (24 in) above the ground. Little information is available concerning communication and perception among Tiger rattlesnakes. However, like other pit vipers, Tiger rattlesnakes have heat-sensing pits (located on each side of the face between the eye and nostril) to detect warm-blooded predators and prey. These snakes ambush much of their prey, but also actively hunt for small rodents and lizards. Their venom is considered the most toxic of all rattlesnakes and like all pit vipers, they inject venom into prey through long, hollow, retractable fangs.
Although it has a comparatively low venom yield, its toxicity is considered to be the second highest of all rattlesnake venoms (next to the mojave), and the second highest of all snakes in the Western Hemisphere. It has a high neurotoxic fraction that is antigenically related to Mojave toxin (see Crotalus scutulatus, venom A), and includes another component immunologically identical to crotamine, which is a myotoxin also found in tropical rattlesnakes (see Crotalus durissus ). A low but significant protease activity is in the venom, although it does not seem to have any hemolytic activity.
Brown (1973) lists an average venom yield of 11 mg (dried venom) and an LD50 value of 0.6 mg/kg IP for toxicity. Other studies give LD50 values of 0.07 mg/kg IP, 0.056 mg/kg IV, and 0.21 mg/kg SC. Minton and Weinstein (1984) list an average venom yield of 6.4 mg (based on two specimens). Weinstein and Smith (1990) list a venom yield of 10 mg.
There is very little information available for bite symptoms. Human bites by the tiger rattlesnake are infrequent, and literature available on bites by this snake is scarce. The several recorded human envenomations by tiger rattlesnakes produced little local pain, swelling, or other reaction following the bite, and despite the toxicity of its venom no significant systemic symptoms. The comparatively low venom yield (6.4–11 mg dried venom) and short 4.0 mm (0.40 cm) to 4.6 mm (0.46 cm) fangs of the tiger rattlesnake possibly prevent severe envenoming in adult humans. However, the clinical picture could be much more serious if the person bitten was a child or a slight build individual. The early therapeutic use of antivenom is important if significant envenomation is suspected. Despite the low venom yield, a bite by this rattlesnake should be considered a life-threatening medical emergency. Untreated mortality rate is unknown but this snake has a very high venom toxicity and its bites are capable of producing major envenomation.
Tiger rattlesnakes are carnivores that generally feed on rodents, but they have also been known to prey on lizards. In addition, these small rattlesnakes have been known to eat fairly large prey, including kangaroo rats, deer mice, packrats, and even spiny lizards.
Tiger rattlesnakes are polygynandrous (promiscuous), and either the male, female, or both have more than one mate within a single mating season. Breeding occurs from late May to mid-August, during the summer monsoon season. Like the majority of rattlesnakes, Tiger rattlesnakes are ovoviviparous with females giving birth to 5 well-developed young. Once born, snakelets break through the embryonic sac and travel a short distance to a safe nook with the siblings. Generally, rattlesnakes invest little in offspring following birth. The smallest known reproductively mature female measured 54 cm (21.3 in) snout-vent length, while the smallest mature male measured 51 cm (20.2 in)
Tiger rattlesnakes are considered endangered at present. However, southern populations on the flatter areas of the coastal plain of Sonora may suffer from habitat loss due to the intensification of agriculture. In addition, the skin and tail rattles of rattlesnakes are often considered valuable and are often sold as souvenirs throughout the American Southwest.
According to IUCN, the Tiger rattlesnake is locally common throughout its range. The total adult population size of this species is unknown but presumably exceeds 10,000 mature individuals. Currently, the Tiger rattlesnake is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
Tiger rattlesnakes prey upon a number of rodent species considered pests by humans throughout their geographic range. They also feed on a number of small vertebrate species and likely help regulate their abundance and distribution.
