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Crotalus unicolorAruba Island Rattlesnake

By Sheri Sanders

Geographic Range

Crotalus unicolor is one of the rarest of the rattlesnakes; it was once found on much of Aruba Island and possibly other West Indies Islands. However, this species is now mainly confined to the southern end of Aruba, due largely to habitat destruction tied to tourism industry development. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; Howard, et al., 2002; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005)

Habitat

Aruba Island rattlesnakes inhabit undisturbed sandy, rocky and arid hillsides of this volcanic island, now totaling only 12 square miles of protected land that includes the Arikok National Park. They are typically found on terraced mountainsides consisting of igneous rock and dry stream beds. The diabase mountains and limestone plateaus have been found to harbor the largest densities of this species, possibly due to the relatively low human presence. They are found from 2 meters above sea level to 188 meters elevation on Mount Jamanota. Oddly, despite the seeming preference for undisturbed areas, Aruba Island rattlesnakes are found within 1 km of the two largest cities on the island.

There is little seasonal variation in temperature in this tropical marine habitat; the average temperature is approximately 81 F (27 C) with daily average highs of 84 F and lows of 78 F. Summers tend to be slightly warmer in temperature – up to average highs of 89 F. ("CIA - The World Factbook", 2006; "AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "CIA - The World Factbook", 2006; "Weather Underground", 2006; "AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; Howard, et al., 2002; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Walter, 1999)

  • Range elevation
    2 to 188 m
    6.56 to 616.80 ft

Physical Description

As with most other rattlesnakes, Aruba Island rattlesnakes are heavy bodied, with a triangular head and a rattle-tipped tail. Dorsal scales are triangular and overlapping, with a slight keel. Diamond-shaped markings are present in a variety of colors ranging from a scarcely discernable white or rust color to an obvious dark brown or blue-gray. These markings blend into a pair of dark lines on either side of the spine which terminate at the head. The body color is also variable from light pink to dark tan, occasionally leaving the markings indistinguishable save for a small band along the spine. There are few markings on the head of this species; at most paired stripes extend from the eye toward the ventral boarder of the jaw. Conspicuous heat-sensing pits are visible below and slightly posterior to the nostrils, one on each side. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake", 2006; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

  • Sexual Dimorphism
  • male larger
  • Range mass
    14 (low) g
    0.49 (low) oz
  • Average length
    1 m
    3.28 ft

Development

Fertilization in Aruba Island rattlesnakes is internal and occurs during the September through January breeding season. Mated females give birth to 5 to 15 live young after four months of gestation. The autonomous young have already developed fully functional venom sacs at this time and average 20 cm in length and 14 g in weight. After their first shedding, the young begin to hunt for their first meal. They may double or triple in size in the first year. At four years for males and five years for females, they reach reproductive maturity and begin to breed. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Aruba Island Rattlesnake", 2006; "Aruba Island Rattlesnake - Crotalus unicolor", 2006; Pough, et al., 2003)

Reproduction

When a female is reproductively receptive, she will emit a pheromone attractant to signal males of this state. Attracted males will compete for the attention of females by “wrestling”. In this form of combat, the two snakes will rear up and entwine the front half of their length in attempts to push the opponent down. Venom is never used in these battles. Once a male has gained access to a female, courtship continues in a fashion common to many snake species. The male comes in contact with the female, lines up along side of her, and runs his lower jaw along the female’s spine. The tongue of the male is continually flicking and the lateral body movement is in a jerky manner, presumably to differentiate courtship from incidental contact. If receptive, the female permits access to her cloaca by lifting her tail. The male then wraps his tail around hers and inserts one prong (of one of the paired hemipenes)into her cloaca. The pair may continue to mate for several hours at a time. ("Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake - Crotalus unicolor", 2006; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

This is an ovoviviparous species; the eggs of the female are retained within the body, and maternal nutrient sharing with the embryos has not been demonstrated. At the end of the four month gestation period, the young emerge from the female as live young, leaving the egg membranes inside the female. Typically 5 to 15 young will emerge during the spring as fully independent snakes. The generation interval has been defined as ten years in all management predictions. Ongoing research will attempt to determine if sperm storing occurs in females. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

  • Breeding interval
    Breeding occurs once yearly.
  • Breeding season
    Breeding occurs from September through January, with births occuring from January through April (birth).
  • Range number of offspring
    5 to 15
  • Average gestation period
    4 months
  • Average time to independence
    0 minutes
  • Average age at sexual or reproductive maturity (female)
    5 years
  • Average age at sexual or reproductive maturity (male)
    4 years

The only parental investment in this species is pre-fertilization and gestational, as the young are independent upon birth. The female is burdened with the majority of this investment, as producing and yolking eggs is energetically expensive. Carrying the developing young for four months is a physical as well as a nutritional burden on her body; the young increase her body size, probably making hunting and feeding difficult.

Male investment consists of sperm production and the energy necessary for courtship and female defense; it is considered negligible compared to that of the female. ("Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Pough, et al., 2003)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Expected lifespan in captivity and in the wild is between 12 and 20 years. ("Aruba Island Rattlesnake", 2006)

  • Typical lifespan
    Status: wild
    12 to 20 years
  • Typical lifespan
    Status: captivity
    12 to 20 years

Behavior

Aruba Island rattlesnakes inhabit a climate that allows year round activity. Normal daily activity is highest during the early morning hours and the late evening; however increased temperatures in summer months may induce these animals to adopt a nocturnal activity cycle. There are few social interactions, with the exception of reproduction and male-male competition for access to females. These snakes are also unlikely to attack unless provoked. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

Home Range

Research to define home range size of Aruba Island rattlesnakes is in progress. There is no evidence of true territorial defense at present. ("Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005)

Communication and Perception

As in all members of the "pitviper" group, subfamily Crotalinae, these rattlesnakes possess a pair of pit organs located below the nostrils. These organs contain infrared receptors that provide information on the body heat, and thus distance, size, and shape, of potential predators and prey. These allow the snakes to hunt during low light conditions, such as during warmer months when they are nocturnal. The directionality of this sense is a result of the physical structure of the pit. Heat information enters the pit much as light enters an eye, and is detected on a curved membrane similar to the way the retina detects the origin of light. It is important to note that this method of detection is more effective in detecting endothermic (mammalian or avian) prey than other ectothermic species and sight is still used in conjunction with infrared sensory detection. ("Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Pough, et al., 2003)

Another form of communication with other species is the series of hollow, keratinized structures that form the rattle at the tip of the tail. The tip of the tail is moved through muscle movement and the vibrations produce a characteristic sound used to warn potential predators. ("Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Pough, et al., 2003)

Pheromones are an important chemical attractant and cue. These rattlesnakes can pick up odors using both the sense of smell and the vomero-nasal (Jacobson’s) organ, where chemicals are supplied by the tongue. The sense of smell is extensive in Aruba Island rattlesnakes, as in most snakes. ("Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Pough, et al., 2003)

Food Habits

These reptiles hunt with the aid of their heat sensing pits, sight, and smell. Targeted species are mainly rodents, birds, and lizards, especially teiids. After prey is located, these snakes position themselves in a striking stance, characterized by an ‘S’ shaped neck. Launching itself forward, these rattlesnakes opens its mouth, allowing two venom delivering fangs to fold down and sink into the prey animal. The venom contains numerous chemicals, most notably proteolytic enzymes which begin to digest the animal before ingestion while other chemicals are responsible for increasing venom uptake and blocking energy to vital systems. After striking, the animal exhibits a period of increased tongue flicking in order to find the envenomatted prey. Interestingly, this behavior is still present when offering live rodents to captive adult animals raised on frozen or thawed (dead) rodents. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake", 2006; O'Connell, et al., 1982; "Aruba Island Rattlesnake - Crotalus unicolor", 2006; Pough, et al., 2003)

Upon debilitation of the prey, these snakes consume their prey whole by unhinging the lower jaw and stretching the mandibular symphysis at the front of the lower jaw. Only feeding perhaps once to a few times per year, the digestive system of these rattlesnakes is reactivated upon ingestion of the food, increasing blood flow to the digestive organs that are dormant during fasting periods, and probably causing a spike in metabolic rate, as observed in other rattlesnakes. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake", 2006; O'Connell, et al., 1982; "Aruba Island Rattlesnake - Crotalus unicolor", 2006; Pough, et al., 2003)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • reptiles

Predation

There are no reported natural predators of Aruba Island rattlesnakes, which are top predators in these habitats. Human encroachment and poaching for rattles and the pet trade are currently the primary threats to the population. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Birds of Aruba - Checklist", 2006; Walter, 1999)

'Crested caracaras Caracara cheriway', 'merlins Falco columbarius', and 'osprey Pandion haliaetus' are possible snake eating species that are found on Aruba, but no specific information about possible predation threats to young rattlesnakes was found. Their cryptic coloration, venom, and habit of warning potential predators of their threat is likely to protect them from much predation. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Birds of Aruba - Checklist", 2006; Walter, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Aruba Island rattlesnakes are top trophic level predators to many small lizards, mammals, and birds. They lack natural predators as adults, their main threat being humans. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; Smith, et al., 1986; Walter, 1999)

Commensal/Parasitic Species
  • Reptilian Calicivirus Crotalus type 1
  • Ophidian Paramyxovirus Pneumonia

Economic Importance for Humans: Positive

Though illegal, a source of some of the threat to these animals is thought to be capture for the pet trade. More recently, increased education has elevated these animals to national symbols, generating tourism to Arikok National Park. The presence of these snakes was instrumental in spurring the development of this park. Increased research efforts have also occurred in recent years, bringing more money to the island. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; Walter, 1999)

Economic Importance for Humans: Negative

Aruba Island rattlesnakes only attack when provoked, but envenomation can be debilitating or life-threatening to a human who is bitten. ("Aruba Island Rattlesnake - Crotalus unicolor", 2006; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

  • Negative Impacts
  • injures humans

Conservation Status

Ecological destruction in the form of charcoal and firewood industry, aloe cultivation, and resort and tourism development has reduced the undisturbed habitat available for Aruba Island rattlesnakes to only twelve square miles. Even in these twelve square miles, there is a growing feral goat population that has been destroying native vegetation. This problem has begun to be addressed with growing support for the preservation of the island's endemic species. Media campaigns and education programs highlight the ecological and economic importance of this native rattlesnake. An improved public image has emerged from articles, interviews, and educational efforts, resulting in the Aruba Island rattlesnake being featured on new currency and postage stamps. Conservation posters are being developed by the Association of Zoos and Aquariums (AZA) to further promote these efforts.

Along with this growing respect for the snakes, the AZA Aruba Island Rattlesnake Species Survival Plan (SSP) helped establish the Arikok National Park. The park consists of 19% of Aruba’s land and includes most of the rattlesnake population. There are also plans underway to remove feral goats and list the species in CITES, Appendix II to ban trade of the snakes into the pet trade and sales of the rattles.

There are currently approximately 230 of these rattlesnakes left in the wild and about 110 managed by the AZA (53 females and 57 males) in zoos. The government donated ten wild caught individuals to help with the breeding program in the SSP and help investigate the details of the breeding physiology and release capabilities. Also, animals not used in breeding are being used to test a vaccine for Paramyxovirus, which has killed several SSP snakes.

Another major issue that is currently being researched is the effects of the introduction of large boas, Boa constrictor, to Aruba. ("AZA - Aruba Island Rattlesnake Fact Sheet", 2000; "Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor", 2006; "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake", 2005; "Aruba Island Rattlesnake - Crotalus unicolor", 2006; Walter, 1999)

Other Comments

Aruba Island rattlesnake venom is thought to be among the most toxic of any rattlesnake. Crotalus unicolor was thought to be extinct before efforts were made to investigate "former" habitats. (Cohn, 2000; "Aruba Island Rattlesnake - Crotalus unicolor", 2006)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Sheri Sanders (author), Michigan State University, James Harding (editor, instructor), Michigan State University.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

island endemic

animals that live only on an island or set of islands.

iteroparous

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).

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

American Zoos and Aquarium Association. 2000. "AZA - Aruba Island Rattlesnake Fact Sheet" (On-line). Accessed October 03, 2006 at http://www.nagonline.net/Fact%20Sheet%20pdf/AZA%20-%20Aruba%20Island%20Rattlesnake%20Fact%20Sheet.pdf#search=%22aruba%20island%20rattlesnake%22.

Sedgwick County Zoo. 2006. "Aruba Island Rattlesnake - Crotalus unicolor" (On-line). Sedgwick County Zoo. Accessed October 03, 2006 at http://www.scz.org/animals/r/airsnake.html.

Lincoln Park Zoo. 2006. "Aruba Island Rattlesnake" (On-line). Accessed October 03, 2006 at http://www.lpzoo.com/animals/FACTS/REPTILES/aruba_rattler.html.

Association of Zoos and Aquariums. 2006. Association of Zoos and Aquariums SSP Masterplan for Aruba Island Rattlesnake, Crotalus unicolor. AZA Aruba Island Rattle Snake SSP: 1-46.

Birds of Aruba. 2006. "Birds of Aruba - Checklist" (On-line). Accessed December 10, 2006 at http://www.arubabirds.com/.

2006. "CIA - The World Factbook" (On-line). Aruba. Accessed November 05, 2006 at https://www.cia.gov/cia/publications/factbook/geos/aa.html.

Jacksonville Zoo and Gardens. 2005. "Jacksonville Zoo and Gardens: Aruba Island Rattlesnake" (On-line). Jacksonville Zoo and Gardens. Accessed October 03, 2006 at http://www.jaxzoo.org/things/biofacts/ArubaIslandRattlesnake.asp.

2006. "Weather Underground" (On-line). Accessed November 25, 2006 at http://www.weatherunderground.com/history/airport/TNCA/2005/11/30/CustomHistory.html?dayend=30&monthend=11&yearend=2006&req_city=NA&req_state=NA&req_statename=NA.

Cohn, J. 2000. Zoos and aquariums are shifting the focus of their conservation efforts to the wild. Bioscience, 50 (7): 564-569. Accessed November 16, 2006 at http://www.bioone.org.proxy2.cl.msu.edu:2047/perlserv/?request=get-document&doi=10.1641%2F0006-3568%282000%29050%5B0564%3AWOTB%5D2.0.CO%3B2.

Howard, , K. Einert, L. Auretta, M. Ushar, G. Ian, L. Rocco, M. Goode, R. Odum. 2002. Distribution of the Aruba Island Rattlesnake, Crotalus unicolor, on Aruba, Dutch West Indies. Caribbean Journal of Science, 38 (2): 126-128. Accessed November 05, 2006 at http://scholar.google.com/scholar?hl=en&lr=&safe=off&q=cache:GT2slLuBXxEJ:caribjsci.org/june02/38_126-128.pdf+crotalus+unicolor.

O'Connell, B., R. Greenlee, J. Bacon, D. Chiszar. 1982. Strike-induced chemosensory searching in old world vipers and new world pit vipers at San Diego Zoo. Zoo Biology, 1(4): 287 - 294. Accessed November 05, 2006 at http://www3.interscience.wiley.com/cgi-bin/abstract/110494680/ABSTRACT?CRETRY=1&SRETRY=0.

Pough, F., R. Andrews, J. Cadle, M. Crump, A. Savitsky, K. Wells. 2003. Herpetology, Third Edition. Upper Saddle River, NJ: Prentice Hall.

Smith, A., M. Anderson, D. Skilling, J. Barlough, P. Ensley. 1986. First isolation of calicivirus from reptiles and amphibians. American Journal of Veterinary Research, 48(8): 1718-1721. Accessed October 16, 2006 at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3019189&dopt=Citation.

Walter, M. 1999. "Some Species Get No Respect - protection for the Aruba Island rattlesnake" (On-line). Find Articles.com. Accessed October 03, 2006 at http://www.findarticles.com/p/articles/mi_m0FRO/is_4_132/ai_55198442.

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