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Crotalus enyoLower California Rattlesnake

By Kendall Lewis

Geographic Range

Baja California rattlesnakes (Crotalus enyo) are native to the Nearctic region and are endemic to Baja California Peninsula. Their range extends from the southern tip of the peninsula as far north as the San Quintin Valley in central Baja California, Mexico. Baja California rattlesnakes can also be found on multiple islands off the coast of the Baja California peninsula, both in the Gulf of California and in the Pacific Ocean. (Hollingsworth and Frost, 2007)

Habitat

Baja California rattlesnakes inhabit arid lowlands and montane regions, including deserts, canyons, and sand dunes. They typically live in areas where they can shelter in rocky outcrops or under vegetative cover from desert tolerant plants, including shrubs such as slipper plants (Pedilanthus macrocarpus), cacti such as creeping devils (Stenocereus eruca), and trees such as Boojum trees (Fouquieria columnaris). They use old mammal burrows or hollow spaces underneath rocks, logs, and live plants to conceal themselves from predators and prey.

Baja California rattlesnakes can live in areas near human settlements and may shelter in trash piles or underneath areas of houses such as porches, where they are likely attracted by the presence of prey species. There is no elevational range reported for Baja California rattlesnakes. (Douglas, et al., 2006; Goldberg and Beaman, 2003; Hollingsworth and Frost, 2007; Minnich and Vizcaino, 1998)

Physical Description

Baja California rattlesnakes vary in coloration between tan, pale brown, dark brown, grayish brown, or silvery gray depending on the individual. The anterior portions of their body are darker than their posterior portions. Baja California rattlesnakes have 28 to 42 blotches that are reddish to yellowish brown with black edges along their dorsal sides. The blotches near their heads and anterior portions are subrectangular, whereas the blotches near their midbodies are more hexagonal in shape. They have transverse pale bars crossing their supraocular scales and dark spots extending from the posterior edge of their supraocular scales to the parietal region of their heads. Between these blotches is a pale brown stripe that extends from the area between their eyes to their necks. Baja California rattlesnakes have ventral sides that are cream in color, but can be heavily mottled with gray or brown. They have 4 to 8 rings of specialized scales that make up their rattles, The proximal regions of their rattles are black, but the distal regions of their rattles are light brown in color.

Baja California rattlesnakes measure up to 89.8 cm in length. As adults, Baja California rattlesnakes exhibit sexual dimorphism, with males larger than females on average. However, as juveniles, both males and females range from 20.6 cm to 22.2 cm. Juveniles have similar coloration to adults.

Baja California rattlesnakes have 23 to 27 rows of dorsal scales on their midbodies, with an average of 25 rows. The number of ventral scales and subcaudal scales differs between sexes. Males typically have 159 to 168 ventral scales and 22 to 28 subcaudal scales whereas females have 161 to 177 ventral scales and 18 to 23 subcaudal scales. Both males and females have 12 to 15 scales supralabial scales and 11 to 16 infralabial scales. They have 2 to 3 preocular scales and 4 to 5 rows of scales between their supraocular scales. Baja California rattlesnakes have 1 to 8 loreal scales, 2 internasal scales and 2 canthal scales. (Beaman and Grismer, 1994)

  • Sexual Dimorphism
  • male larger
  • Range length
    898 (high) mm
    35.35 (high) in

Development

Baja California rattlesnakes are ovoviviparous. Females spend 2 to 5 months gestating eggs, which hatch internally and are born precocial. Newborns range in length from 20.6 to 22.2 cm. Baja California rattlesnakes exhibit indeterminate growth, although growth rates decrease when they reach maturity. Females reach sexual maturity after 4 to 6 years, whereas males reach maturity after 7 to 13 years. Males are larger than females, on average, with a maximum recorded length of 89.8 cm. (Douglas, et al., 2006; Ruiz-Sanches, et al., 2019)

Reproduction

Baja California rattlesnakes reproduce sexually and have a polygynous mating system. They find potential mates by releasing and detecting sex-specific pheromones. Males compete aggressively with other males for access to females, but their competition is non-violent. When a male and female copulate, they line up their cloacae so that males can deposit sperm. Once their cloacae are aligned, males evert a pair of reproductive organs, called hemipenes, and insert them into the cloaca of their mate. In some instances, males will wrap their tails around the cloacal region of their mate. Once males insert their hemipenes, they exhibit mild twitching movements that only end once they separate from their mate. (Armstrong and Murphy, 1979; Goldberg and Beaman, 2003)

Baja California rattlesnakes reproduce sexually with internal fertilization. They are ovoviviparous, meaning eggs hatch internally and females give birth to live young. Baja California rattlesnakes have a two-year breeding cycle, meaning individuals breed every other year, with a breeding season in early spring. Females have clutches of 2 to 9 young, with larger females having larger clutches. Newborn Baja California rattlesnakes are immediately independent and reach maturity at different times depending on sex. Females reach sexual maturity after 4 to 6 years, whereas males reach sexual maturity after 7 to 13 years. Newborns measure 20.6 to 22.2 cm in length, but individuals can reach up to 89.8 cm in length as adults. (Goldberg and Beaman, 2003)

  • Breeding interval
    Baja California rattle snakes breed every other year
  • Breeding season
    Baja California rattlesnakes breed in late spring
  • Range number of offspring
    2 to 9
  • Range gestation period
    2 to 5 months
  • Average time to independence
    0 minutes
  • Range age at sexual or reproductive maturity (female)
    4 to 6 years
  • Range age at sexual or reproductive maturity (male)
    7 to 13 years

Baja California rattlesnakes do not exhibit extended parental care. Females carry developing eggs internally for 2 to 5 months, but show no parental involvement once young are born. Males exhibit no parental care beyond the act of mating. (Goldberg and Beaman, 2003)

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

Lifespan/Longevity

In captivity, Baja California rattlesnakes can live up to 17.1 years. There is limited information regarding the lifespans of wild Baja California rattlesnakes. However, another species in their genus, timber rattlesnakes (Crotalus horridus) can live 16 to 22 years in the wild. It is likely that Baja California rattlesnakes have similar lifespans in the wild. (Snider and Bowler, 1992)

  • Range lifespan
    Status: captivity
    17.1 (high) years

Behavior

Baja California rattlesnakes are crepuscular, although they also hunt nocturnally. They emerge during the day to bask in solar-exposed areas, such as rocks or bare patches of ground. Besides basking behaviors, Baja California rattlesnakes mostly remain hidden among rocks or vegetation during the day. They are mobile and social, typically living in small groups. Even though they are mobile, Baja California rattlesnakes do not migrate. They reproduce sexually and females give birth to 2 clutches of 2 to 9 young every other year. Baja California rattlesnakes brumate in the winter to conserve energy when temperatures are lowest.

During mating season, male Baja California rattlesnakes compete aggressively with each other for mates, but their competitive behaviors are non-violent. Competitive behaviors include aggressive posturing and hissing. They also hiss and use the rattles on their tails to intimidate nearby predators. Baja California rattlesnakes are venomous, but mostly strike at prey and will only strike at predators that are not deterred by their rattles. They are small and do not inject large amounts of venom in their bites. (Chiszar, 1977; Chiszar, et al., 1980; Chiszar, et al., 1981; Hollingsworth and Frost, 2007; Marmie, et al., 1990; Olivier, 2008)

Home Range

There is little information regarding home range sizes of Baja California rattlesnakes. However, another species in the same genus, eastern diamondback rattlesnakes (Crotalus adamanteus) maintain one home range throughout their life, but are not territorial. Female eastern diamondback rattlesnakes tend to maintain smaller home ranges compared to males. It is likely that Baja California rattlesnakes exhibit similar patterns of behavior regarding home ranges. (Timmerman, 1995)

Communication and Perception

Baja California rattlesnakes primarily rely on chemical cues to perceive their environment. They have forked tongues that pick up chemicals from the environment and deliver them to the vomeronasal organ, which processes chemical signals to determine their source. Baja California rattlesnakes use their tongues to sense chemicals released by predators, prey, and conspecifics. Baja California rattlesnakes do not have external ears, but are highly sensitive to vibrations propagating through the ground, such as approaching footsteps of predators or prey. They also have pit organs, which allow them to detect infrared radiation from warm objects, such as endothermic animals.

Baja California rattlesnakes also communicate acoustically, hissing and rattling their tails to intimidate predators or attract mates. They also use visual communication to intimidate predators or potential competitors for mates. When threatened, Baja California rattlesnakes raise their heads and coil the posterior section of their bodies to appear larger and prepare to strike. Males also use aggressive postures when competing with other males for mates. While copulating, Baja California rattlesnakes use tactile communication with their mates. (Chiszar, 1977; Chiszar, et al., 1982; Taylor, 2001)

Food Habits

Baja California rattlesnakes are considered carnivores. They feed mainly on small mammals and reptiles, but sometimes consume arthropods. A 2016 study on Baja California rattlesnakes in the Cape region of the Baja California peninsula found that their diets consisted of 83.3% rodents and 16.7% lizards. Baja California rattlesnakes eat items that are dead or alive, as long as they can swallow them whole. There are no apparent differences in their diets between dry and rainy seasons.

Known prey items of Baja California rattlesnakes include rodents such as Botta’s pocket gophers (Thomomys bottae), spiny pocket mice (Chaetodipus spinatus), kangaroo rats (Dipodomys), and deer mice (genus Peromyscus). Baja California rattlesnakes also consume lizards, including dunes sagebrush lizards (Sceloporus arenicolus), common side botched lizards (Uta stansburiana), orange-throated whiptails (Aspidocelis hyperythra), Baja California spiny-tailed iguanas (Ctenosaura hemilopha), and Hunsaker's spiny lizards (Sceloporus hunsakerii). Baja California rattlesnakes have also been reported to eat centipedes in the genus Scolopendra. (Arnaud, et al., 2016; Chiszar, 1977; Taylor, 2001)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
    • eats non-insect arthropods
  • Animal Foods
  • mammals
  • reptiles
  • terrestrial non-insect arthropods

Predation

Baja California rattlesnakes serve as prey for mammals, such as bobcats (Lynx rufus), coyotes (Canis latrans), and wild boars (Sus scrofa). They are also eaten by birds of prey, such as red-tailed hawks (Buteo jamaicensis) and turkey vultures (Cathartes aura). Baja California rattlesnakes have cryptic coloration, which helps them blend in with their surroundings and hide from predators. If they are detected by predators, Baja California rattlesnakes will adopt aggressive body postures, hiss, and use their rattles to intimidate predators. Baja California rattlesnakes also produce venom, which can cause serious injury or death to animals that they bite. (Harmel, et al., 2020)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Baja California rattlesnakes eat rodents, small reptiles, and arthropods. They likely play a role in controlling population sizes of prey species. Baja California rattlesnakes also serve as prey for larger animals, including carnivorous mammals and birds of prey.

Baja California rattlesnakes are known to be hosts for tapeworms in the genus Mesocestoides and acanthocephalans in the family Oligacanthorhynchidae. (Soria-Díaz, et al., 2019)

Commensal/Parasitic Species
  • Tapeworms (genus Mesocestoides)
  • Acanthocephalans (family Oligacanthorhynchidae)

Economic Importance for Humans: Positive

Baja California rattlesnakes that live near human residences may control populations of rodent and insect pests. However, there is currently no quantitative research that explicitly addresses this possibility. (Chiszar, 1977; Chiszar, et al., 1980; Chiszar, et al., 1981)

Economic Importance for Humans: Negative

Baja California rattlesnakes produce venom that can cause serious health issues, although they typically do not strike unless provoked. Baja California rattlesnake venom contains hemotoxins that affect the circulatory system. Furthermore, the antivenom that negates the toxin can cause allergic reactions or anaphylaxis in some people. Such reactions can be life-threatening and require immediate medical treatment. (Purohit, 2019; Putman and Clark, 2015; Radcliffe, et al., 1980)

  • Negative Impacts
  • injures humans

Conservation Status

Baja California rattlesnakes are classified as a species of "Least Concern" on the IUCN Red List. They have no special status on U.S. Federal List, CITES, or the State of Michigan List.

Baja California rattlesnakes typically avoid human activity, which makes it difficult to determine conservation threats to their populations. They have been observed as roadkill and thus suffer from increased mortality near roadways. Furthermore, agricultural development is replacing and fragmenting their natural habitat, although these effects are currently concentrated in the northern part of their geographic range. Finally, because they are restricted to the Baja California peninsula - a relatively small geographic range - future climate change and habitat loss may have a large impact on the health of their populations.

There are currently no conservation efforts in place specifically for Baja California rattlesnakes. However, there are populations of Baja California rattlesnakes in protected areas, such as national parks. It is important to gain a better understanding of Baja California rattlesnake life history to make informed conservation decisions. (Carbajal Márquez, 2013; Hollingsworth and Frost, 2007)

Contributors

Kendall Lewis (author), Radford University, Sierra Felty (editor), Radford University, Karen Powers (editor), Radford University, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

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.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

infrared/heat

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

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).

motile

having the capacity to move from one place to another.

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.

polygynous

having more than one female as a mate at one time

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

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

venomous

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

visual

uses sight to communicate

References

Armstrong, B., J. Murphy. 1979. The Natural History of Mexican Rattlesnakes. Lawrence, Kansas: University of Kansas Museum of Natural History.

Arnaud, G., R. Carbajal-Márquez, M. Martins, G. Quintero-Díaz. 2016. Diet of Crotalus enyo (Serpentes: Viperidae) from the Baja California cape region, Mexico. Acta Zoológica Mexicana, 31/1: 45-48.

Beaman, K., L. Grismer. 1994. Crotalus enyo (Cope) Baja California rattlesnake. Catalogue of American Amphibians and Reptiles, 589: 1-6.

Carbajal Márquez, R. 2013. Uso de Hábitat de Crotalus enyo (Serpentes: Viperidae) en la Región del Cabo, Baja California Sur, México (Master's Thesis). La Paz, Baja California Sur, Mexico: Centro de Investigaciones Biológicas del Noroeste.

Chiszar, D. 1977. Analysis of the behavioral sequence emitted by rattlesnakes during feeding episodes: I. Striking and chemosensory searching. Behavioral Biology, 21/3: 418-425.

Chiszar, D., C. Radcliffe, T. Byers, R. Stoops. 2017. Prey capture behavior in nine species of venomous snakes. The Psychological Record, 36: 433-438.

Chiszar, D., C. Radcliffe, B. O'Connell, H. Smith. 1982. Analysis of the behavioral sequence emitted by rattlesnakes during feeding episodes II. Duration of strike-induced chemosensory searching in rattlesnakes (Crotalus viridis, C. enyo). Behavioral and Neural Biology, 34/3: 261-270.

Chiszar, D., C. Radcliffe, B. O'Connell, H. Smith. 1980. Strike-induced chemosensory searching in rattlesnakes (Crotalus enyo) as a function of disturbance prior to presentation of prey. Transactions of the Kansas Academy of Sciences, 83/4: 230-234.

Chiszar, D., C. Radcliffe, H. Smith, H. Bashinski. 1981. Effect of prolonged food deprivation on response prey odors by rattlesnakes. Herpetologica, 37/4: 237-243.

Douglas, M., M. Douglas, G. Schuett, L. Porras. 2006. Evolution of rattlesnakes (Viperidae; Crotalus) in the warm deserts of western North America shaped by Neogene vicariance and Quaternary climate change. Molecular Ecology, 15/11: 3353-3374.

Ernst, C., E. Ernst. 2012. Venomous Reptiles of the United States, Canada, and Northern Mexico: Volume 2 Crotalus. Baltimore, Maryland: The John Hopkins University Press.

Goldberg, S., K. Beaman. 2003. Reproduction in the Baja California rattlesnake, Crotalus enyo. Bulletin Southern California Academy of Sciences, 102/1: 39-42.

Harmel, M., H. Crowell, J. Whelan, E. Taylor. 2020. Rattlesnake colouration affects detection by predators. Journal of Zoology, 311/4: 260-268.

Hollingsworth, B., D. Frost. 2007. "Crotalus enyo" (On-line). The IUCN Red List of Threatened Species 2007: e.T64316A12765256. Accessed September 05, 2022 at https://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T64316A12765256.en.

Marmie, W., S. Kuhn, D. Chiszar. 1990. Behavior of captive-raised rattlesnakes (Crotalus enyo) as a function of rearing conditions. Zoo Biology, 9/3: 241-246.

Minnich, R., E. Vizcaino. 1998. Land of Chamise and Pines: Historical Accounts and Current Status of Northern Baja California's Vegetation. Berkeley, California: University of California Press.

Olivier, R. 2008. Da Baja California ratelslang, Crotalus enyo en een kweekverslag van de Rosario ratelslang, Crotalus enyo furvus. Lacerta, 66/1: 30-39.

Purohit, M. 2019. "Baja California rattlesnake bite" (On-line). DoveMed. Accessed November 16, 2022 at https://www.dovemed.com/diseases-conditions/baja-california-rattlesnake-bite/.

Putman, B., R. Clark. 2015. Habitat manipulation in hunting rattlesnakes (Crotalus species). The Southwestern Naturalist, 60/4: 374-377.

Radcliffe, C., D. Chiszar, B. O'connell. 1980. Effects of prey size on poststrike behavior in rattlesnakes (Crotalus durissus, C. enyo, and C. viridis). Bulletin of the Psychonomic Society, 16/6: 449-450.

Ruiz-Sanches, E., G. Arnaud, O. Cruz-Andres, F. Garcia-De Leon. 2019. Phylogenetic relationships and origin of the rattlesnakes of the Gulf of California islands (Viperidae: Crotalinae: Crotalus). The Herpetological Journal, 29: 162-172. Accessed November 19, 2022 at https://doi.org/10.33256/hj29.3.162172.

Snider, A., J. Bowler. 1992. Longevity of Reptiles and Amphibians in North American Collections, Second Edition. Ithaca, New York: Society for the Study of Amphibians and Reptiles.

Soria-Díaz, L., J. Rábago-Castro, H. Domínguez-Vega, Y. Gómez-Ortíz, J. Manjarrez, L. Garrido-Olvera. 2019. Parasites in feces of the endemic rattlesnake, Crotalus triseriatus (Serpentes: Viperidae), from Mexican highlands. Zoologia, 36: 1-6. Accessed October 31, 2022 at https://doi.org/10.3897/zoologia.36.e29587.

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