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==Predators==
==Predators==
There is little to no information available regarding predators specific to tiger rattlesnakes. However, likely predators include [[hawk]]s, [[eagle]]s, [[coyotes]], and other snakes. Their cryptic coloration helps camouflage them from potential predators and helps reduce risk of predation. If disturbed, they rapidly shake their rattle and may strike in defense. Tiger rattlesnakes are known to have an irascible temperament and are easily excitable and can be quite aggressive.<ref name=B&D>{{cite journal|last=Beaupre|first=Steven J.|coauthors=Duvall, David J.|title=Integrative Biology of Rattlesnakes|journal=BioScience|year=1998|month=July|volume=48|issue=7|pages=531-538|url=http://www.jstor.org/discover/10.2307/1313315?uid=3739448&uid=2129&uid=2&uid=70&uid=3737720&uid=4&sid=21102777678891|accessdate=20 October 2013}}</ref>
There is little to no information available regarding predators specific to tiger rattlesnakes. However, likely predators include [[hawk]]s, [[eagle]]s, [[coyotes]], and other snakes. Their cryptic coloration helps camouflage them from potential predators and helps reduce risk of predation. If disturbed, they rapidly shake their rattle and may strike in defense. Tiger rattlesnakes are known to have an irascible temperament and are easily excitable and can be quite aggressive.<ref name=B&D>{{cite journal|last=Beaupre|first=Steven J.|coauthors=Duvall, David J.|title=Integrative Biology of Rattlesnakes|journal=BioScience|year=1998|month=July|volume=48|issue=7|pages=531-538|url=http://www.jstor.org/discover/10.2307/1313315?uid=3739448&uid=2129&uid=2&uid=70&uid=3737720&uid=4&sid=21102777678891|accessdate=20 October 2013}}</ref>

==Reproduction==
Tiger rattlesnakes are polygynandrous, and either the male, female, or both have more than one mate within a single breeding season. Little else is known of the reproductive behavior of this species. The reproductive behavior of this species is thought to be similar to the that of ''Crotalus atrox'' and ''Crotalus scutulatus''. Copulation in viperids can take minutes, hours, or days and can occur multiple times within a couple of days.<ref name=Gberg>{{cite journal|last=Goldberg|first=S.|title=.Reproduction in the Tiger rattlesnake, Crotalus tigris (Serpentes: Viperidae)|journal=The Texas Journal of Science|year=1999|volume=51|issue=1|pages=31-36|accessdate=20 October 2013}}</ref>

Tiger rattlesnake females follow a biennial reproductive cycle. Males follow a seasonal reproductive cycle, where sperm is stored in the vasa deferentia during winter. Breeding occurs from late May to mid August, during the summer monsoon season. Like the majority of rattlesnakes, tiger rattlesnakes are ovoviviparous. Mean clutch size for is 4 to 6 young. The smallest known sexually reproducing female measured {{convert|541|mm|in cm|abbr=on}} snout-vent length (SVL), while the smallest mature male measured {{convert|512|mm|in cm|abbr=on}} SVL.<ref name=Lowe86/><ref name=Gberg/><ref name=MR/>


==Conservation status==
==Conservation status==

Revision as of 04:25, 20 October 2013

Crotalus tigris
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Subphylum:
Vertebrata
Class:
Reptilia
Order:
Squamata
Suborder:
Serpentes
Family:
Viperidae
Subfamily:
Crotalinae
Genus:
Crotalus
Species:
C. tigris
Binomial name
Crotalus tigris
Kennicott, 1859
Synonyms
Common names: tiger rattlesnake, tiger rattler.[2]

Crotalus tigris is a venomous pit viper species found in the southwestern United States and northwestern Mexico. No subspecies are currently recognized.[3] 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.[4]

Physical Description

Tiger rattlesnakes are easily identified by their small, spade shaped head, which is about 1/25 of their total body length. They have 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 the body, 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. Also mid-dorsally, the crossbands become wider than the spaces that separate them. Posteriorly, the crossbands become darker and more clearly defined. They have 6 to 10 posterior rings. The markings on the head are mostly vague and irregular, although towards the rear of the head, a few dark markings may be arranged as paired occipital blotches and upper temporal streaks. The most distinguishable mark on the head is a dark cheek strip. Dorsal scales are keeled and in 21 to 27 rows. A relatively small species, individuals can weigh as much as 454 g (16.0 oz) and can range in length from 460 mm (18 in) to 910 mm (36 in), with an average length of 609 mm (24.0 in). The largest specimen on record measured 88.5 cm (34.8 in) (Klauber, 1956), until H.M. Smith and Brodie (1982) reported a maximum length of 91.2 cm (35.9 in).[5]Females have 164 to 177 ventral scales, and males have 158 to 172 ventral scales. Females have 16 to 21 caudal scales, and males have 23 to 27 caudal scales and are typically larger than females. They have relatively small eyes with an elliptical pupil.[4][6][7]

Distribution and Geographic range

The species' range extends from central Arizona south through south-central Arizona in the United States[8][9][10], to southern Sonora, Mexico, including Isla Tiburón in the Gulf of California and was recently discovered in the southern Peloncillo Mountains of Arizona. The type locality is described as "Sierra Verde and Pozo Verde". The latter is a spring located on the Sonora side of the US-Mexico border, near Sasabe. According to Stejneger (1893), this spring is on the western slope of the southern Sierra Verde, which is also known as the Sierra del Pozo Verde.[1] In these areas, the Tiger rattlesnake is observed at elevations from sea level to about 1,465 metres (4,806 ft)[11][12] Reported occurrences at higher elevations have not been confirmed.[12]

Habitat and Ecology

The Tiger rattlesnakes habitats include rocky desert canyons, foothills, and bajadas, in vegetation zones ranging from thornscrub, ocotillo-mesquite-creosote bush, saguaro-paloverde, mesquite grassland, and chaparral to tropical deciduous forest (southern Sonora) and the lower edge of oak woodland.[4][11][8] In southeastern Arizona, this snake occurs strictly in rocky areas in winter and spring but uses edges of arroyos in summer.[13] It is a terrestrial species but may climb into low vegetation.

Tiger rattlesnakes have also often been observed in the foothills, rocky canyons, and ravines of deserts or mesquite grasslands from 1,000 metres (3,300 ft) to 5,000 metres (16,000 ft) in elevation, throughout their geographic range. Tiger rattlesnakes also inhabit escarpments, outcroppings and cliff-faces in thorny scrub desert habitat.[14][6][11] In southeastern Arizona, mean home range size was 3.48 hectares (0.0134 sq mi; 0.0348 km2), and individuals moved an average of 33 metres (108 ft) per day during the active season.[13]

Behavior and Habits

Tiger rattlesnakes are terrestrial (ground-dwelling) snakes and are nocturnal during the hot summer months (June-August), but become diurnal and crepuscular in during the fall season. It hibernates during the cold months of late fall and winter. There is little information 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.[15]

This snake is inactive in cold temperatures (December/January) and extreme heat (July/August). It may be active both day and night; daytime activity consists mainly of basking on cool days. These snakes are often observed being active after warm rains.[11] In southeastern Arizona, they are active mainly from March to October.[13]

Diet and Food Habits

Tiger rattlesnakes generally feed on small mammals such as pocket mice, kangaroo rats, deer mice, and woodrats. They are also known to prey on lizards. This species' venom is considered the most toxic of all rattlesnakes and contains a myotoxin known to cause muscle necrosis and a neurotoxin similar to Mojave toxin. Like all venomous snakes, tiger rattlesnakes inject venom into prey through long, hollow, retractable fangs. If envenomated prey crawl into a small crevice, this species is especially suited for extracting them due to its unusually small head.[11][14][15]

Predators

There is little to no information available regarding predators specific to tiger rattlesnakes. However, likely predators include hawks, eagles, coyotes, and other snakes. Their cryptic coloration helps camouflage them from potential predators and helps reduce risk of predation. If disturbed, they rapidly shake their rattle and may strike in defense. Tiger rattlesnakes are known to have an irascible temperament and are easily excitable and can be quite aggressive.[16]

Reproduction

Tiger rattlesnakes are polygynandrous, and either the male, female, or both have more than one mate within a single breeding season. Little else is known of the reproductive behavior of this species. The reproductive behavior of this species is thought to be similar to the that of Crotalus atrox and Crotalus scutulatus. Copulation in viperids can take minutes, hours, or days and can occur multiple times within a couple of days.[17]

Tiger rattlesnake females follow a biennial reproductive cycle. Males follow a seasonal reproductive cycle, where sperm is stored in the vasa deferentia during winter. Breeding occurs from late May to mid August, during the summer monsoon season. Like the majority of rattlesnakes, tiger rattlesnakes are ovoviviparous. Mean clutch size for is 4 to 6 young. The smallest known sexually reproducing female measured 541 mm (21.3 in; 54.1 cm) snout-vent length (SVL), while the smallest mature male measured 512 mm (20.2 in; 51.2 cm) SVL.[8][17][18]

Conservation status

This species is classified as Least Concern on the IUCN Red List of Threatened Species (v3.1, 2001).[19] Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007.[20]

Population

The population trend of the tiger rattlesnake is considered to be stable. On a range-wide scale, Campbell and Lamar (2004) mapped 33 collection sites. Lowe et al. (1986) stated that the species is known from approximately 100 localities throughout the range. The adult population size is unknown but presumably exceeds 10,000. This snake is fairly common in some areas, but "some local populations seem small" (Ernst and Ernst 2003). Its extent of occurrence, area of occupancy, number of subpopulations, and population size are probably relatively stable or declining at a rate of less than 10% over 10 years or three generations.[19]

Threats

Southern populations on the flatter areas of the coastal plain of Sonora are probably losing habitat due to the intensification of agriculture. Overall, however, this species is not seriously threatened.[19]

Relevance to Humans and Ecosystems

Negative

Although tiger rattlesnakes are reluctant to strike, they are highly venomous, cantankerous and as a result pose a potential threat to humans. Their venom contains a neurotoxin called Mojave toxin and a myotoxin known to cause muscle necrosis. Although venom production is low compared to other rattlesnakes, their venom is the most toxic of any snake in the Western Hemisphere. The combination of neuro- and mytoxins in their venom makes them extremely dangerous to humans.[21]

Positive

In general, rattlesnake skin and tail rattles are often considered valuable and are often sold as souvenirs throughout the American Southwest. Rattlesnake venom is often used in biomedical research investigating neurological diseases. Finally, tiger rattlesnakes prey upon a number of rodent species considered pests by humans throughout their geographic range. Tiger rattlesnakes feed on a number of small vertebrate species and likely help regulate their abundance and distribution. There is no information regarding parasites specific to this species.[18]

Venom

Although it has a comparatively low venom yield, [22] its toxicity is considered to be the highest of all rattlesnake venoms, and the 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 there does not seem to be any hemolytic activity.[23]

Brown (1973) lists an average venom yield of 11 mg (dried venom) and an LD50 value of 0.6 mg/kg IP for toxicity.[24] Other studies give LD50 values of 0.07 mg/kg IP, 0.056 mg/kg IV, and 0.21 mg/kg SC.[25] 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.[26]

Essentially no information available for bite symptoms. 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 is known to cause major envenomation.[23][26]

See also

References

  1. ^ a b McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. ISBN 1-893777-00-6 (series). ISBN 1-893777-01-4 (volume).
  2. ^ Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. ISBN 0-8014-0463-0.
  3. ^ "Crotalus tigris". Integrated Taxonomic Information System. Retrieved 16 May 2007.
  4. ^ a b c Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
  5. ^ Smith, H.M. and Edmund D. Brodie, Jr. 1982. Reptiles of North America: A Guide to Field Identification. Golden Press. New York. 240 pp. ("TIGER RATTLESNAKE (Crotalus tigris)", pp. 204-205.)
  6. ^ a b Ernst, Carl H. (1992). Venomous Reptiles of North America. USA: Smithsonian Inst Pr. ISBN 1560981148.
  7. ^ Fowlie, JA (1965). The Snakes of Arizona. USA: Azul Quinta Press. {{cite book}}: |access-date= requires |url= (help)
  8. ^ a b c Lowe, CH (1986). The Venomous Reptiles of Arizona. USA: Arizona Game and Fish Department. ISBN 0917563034.
  9. ^ Painter, CW (1993). "Crotalus tigris (tiger rattlesnake)". Herpetological Review. 24 (4): 155–156. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Howland, JM (2002). "Crotalus tigris (Tiger Rattlesnake). Geographic Distribution". Herpetological Review. 33 (2): 149. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ a b c d e Stebbins, Robert C. (2003). A Field Guide to Western Reptiles and Amphibians. USA: Houghton Mifflin Harcourt; 3 edition. ISBN 0395982723.
  12. ^ a b Campbell, Lamar, Jonathan, William (2004). The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates; Two-volume set edition. ISBN 0801441412.{{cite book}}: CS1 maint: multiple names: authors list (link)
  13. ^ a b c Beck, DD (1995). "Ecology and energetics of three sympatric rattlesnakes in the Sonoran Desert". Journal of Herpetology. 29 (2): 211–223. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)
  14. ^ a b Bartlett, Tennant, R.D., Alan (1999). Snakes of North America: Western Region. USA: Taylor Trade Publishing. ISBN 0877193126.{{cite book}}: CS1 maint: multiple names: authors list (link)
  15. ^ a b Brennan, T. C. "The Reptiles and Amphibians of Arizona. An Online Field Guide". Retrieved 20 October 2013.
  16. ^ Beaupre, Steven J. (1998). "Integrative Biology of Rattlesnakes". BioScience. 48 (7): 531–538. Retrieved 20 October 2013. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  17. ^ a b Goldberg, S. (1999). ".Reproduction in the Tiger rattlesnake, Crotalus tigris (Serpentes: Viperidae)". The Texas Journal of Science. 51 (1): 31–36. {{cite journal}}: |access-date= requires |url= (help)
  18. ^ a b Rubio, Manny (1998). Rattlesnake - Portrait of a Predator. Smithsonian Institution Press; 1St Edition edition. ISBN 1560988088.
  19. ^ a b c Crotalus tigris at the IUCN Red List. Accessed 13 September 2007.
  20. ^ 2001 Categories & Criteria (version 3.1) at the IUCN Red List. Accessed 13 September 2007.
  21. ^ Powell, RL (2004). "Identification of a Neurotoxic Venom Component in the Tiger Rattlesnake, Crotalus tigris". Journal of Herpetology. 38 (1): 149–152. doi:http://dx.doi.org/10.1670/76-03N. Retrieved 20 October 2013. {{cite journal}}: Check |doi= value (help); External link in |doi= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  22. ^ Weinstein and Smith (1990)
  23. ^ a b Norris R. 2004. Venom Poisoning in North American Reptiles. In Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. ISBN 0-8014-4141-2.
  24. ^ Brown JH. 1973. Toxicology and Pharmacology of Venoms from Poisonous Snakes. Springfield, Illinois: Charles C. Thomas. 184 pp. LCCCN 73-229. ISBN 0-398-02808-7.
  25. ^ CALVETE, Juan J. (3). "Snake Venomics of Crotalus tigris: The Minimalist Toxin Arsenal of the Deadliest Neartic Rattlesnake Venom". Journal of Proteome Research. 11 (2): 1382–1390. doi:10.1021/pr201021d. Retrieved 19 October 2013. {{cite journal}}: Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  26. ^ a b "University of Adelaide Clinical Toxinology Resources".

Further reading

  • Kennicott, R. In Baird, S.F. 1859. Reptiles of the Boundary, with Notes by the Naturalists of the Survey. In Report of the United States and Mexican Boundary Survey, Under the Order of Lieut. Col. W.H. Emory, Major First Cavalry, and United States Commissioner, vol. 2, no. 2. Department of the Interior. Washington, District of Columbia. 35 pp.
  • Klauber, L.M. 1956. Rattlesnakes: Their Habits, Life Histories and Influence on Mankind. 2 volumes. University of California Press. Berkeley, California. 1,533 pp.
  • Stejneger, L.H. 1893. Annotated List of the Reptiles and Batrachians Collected by the Death Valley Expedition in 1891, with Descriptions of New Species. North American Fauna, No. 7, Part II, pp. 159-228.
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