There are stories circulating that rattlesnakes are evolving and losing their rattles because they no longer use them due to the fact that it's safer for them to remain silent around humans. There's no real proof that this is happening. Here's more information about that.
The tail of a newborn juvenile has only a single silent yellow button on the end of its tail. As it grows it will add rattle segments at the end of the tail behind the button, which remains at the end.
Variations in Appearance Near the Southern Range Limit
C. o. oreganus near its southern range limit is variable in appearance, sometimes with markings similar to C. o. lutosus. Identification of rattlesnakes found in this region can be confusing and open to debate. I have received several comments that I might have mis-identified snakes from this region - that they could be intergrades or hybrids, or that the Kern County snake from the Greenhorn Mountains shown in the row below on the left is actually C. o. lutosus. However, it is a C. o. oreganus, based on appearance, location, and some preliminary genetics work that has been done in the area on other rattlesnakes. The Inyo County rattlesnake depicted in the row below on the far right from the southern Sierras has been identified by various viewers of the photo as C. o. oreganus or C. o. lutosus, but it is actually a young Panamint Rattlesnake - Crotalus stephensi. Rumors of C. oreganus x C. stephensi hybrids have not yet been confirmed by genetic analysis. Some of these controversies should be resolved when the results of further studies on these species are published.
According to herpetologist Robert Hansen, who has studied in depth the reptiles and amphibians of the Southern Sierra Nevada Mountains and the surrounding regions: "Among populations of 'oreganus' inhabiting arid landscapes near their southern range limits (e.g., southern San Joaquin Valley, Carrizo Plain), there is a tendency toward small size, light ground color, and reduced dorsal blotch size...features that cause these snakes to superficially resemble lutosus."..."The southern extent of the range of lutosus in eastern California (e.g., the Mono/Inyo counties region) has been mapped in reasonable detail, and thus far, there are no known instances where the ranges of oreganus and lutosus come into contact. However, farther north, where the Sierra Nevada crest is much lower and the potential for populations of oreganus and lutosus to meet is likely greater, careful field studies are lacking. Ultimately, reliance on features of coloration and pattern to distinguish one form from the other in areas of potential contact is not advised."
A Northern Pacific Rattlesnake crossed a mountain road on a windy spring morning in Contra Costa County then coiled defensively at the edge of the road. Concerned with my presence a few yards away, it is seen here sensing the air with its tongue and rattling its tail, then pausing to watch a bicycle speed down the road, then rattling some more.
A juvenile rattlesnake rattles and crawls off a road in the foothills of Fresno County in early Fall.
A Northern Pacific Rattlesnake
shakes its tail.
The snake here is seen slowly following a snake hook with curiosity, not aggression. The hook had been used earlier to pick up a breeding pair of snakes, and we decided that this one was probably a male that smelled the scent of the breeding female on the hook.
Most rattlesnakes will do exactly what this one did when I encountered it in the late afternoon on a mountain road - turn and crawl quickly away, with a little rattling thrown in as a warning. Rattlesnakes are often depicted in fiction as aggressors, leaping and striking viciously, often for no reason other than to give the hero an excuse to kill it to prove himself. The truth is that rattlesnakes are almost always defensive, not offensive, when they encounter humans, wanting nothing more than to escape, and the least heroic thing someone can do is to automatically kill them.
This video begins with a squirrel's high-pitched alarm call coming from a large group of shrubs in the Sierra Nevada mountains. When I got closer the squirrel ran away and I saw this rattlesnake climbing down a branch then farther back into the bushes. Later, after the camera batteries died, the snake returned and crawled outside the shrubs while the squirrel called and ran around outside the bushes near the snake, but outside of its striking range. I suspect the squirrel was harassing the snake to distract it from young squirrels in a nest.
A Northern Pacific Rattlesnake in the Sierra Nevada mountains crawls into a crack and shakes its tail.
Listen to a Northern Pacific
Click on the picture to see more rattlesnake signs.
Rattlesnakes are important members of the natural community. They will not attack, but if disturbed or cornered, they will defend themselves. Reasonable watchfulness should be sufficient to avoid snakebite. Give them distance and respect.
"Rattlesnakes are also among the most reasonable forms of dangerous wildlife: their first line of defense is to remain motionless; if you surprise them or cut off their retreat, they offer an audio warning; if you get too close, they head for cover. Venom is intended for prey so they're reluctant to bite, and 25 to 50 percent of all bites are dry - no venom is injected."Leslie Anthony. Snakebit: Confessions of a Herpetologist. Greystone Books, 2008.
Rattlesnakes are typically described as poisonous, but they are actually venomous.
A poisonous snake is one that is harmful to eat. A venomous snake injects dangerous venom into its victim.
A bite from a rattlesnake can be extremely dangerous, but rattlesnakes should not be characterized as aggressive and vicious, striking and biting without provocation, as they are often shown. If rattlesnakes are given some space and enough time to escape to a safe place, they will usually just crawl away as fast as possible to avoid confrontation. Rattlesnakes will not strike without a reason: they will strike at a potential meal and they will defend themselves from anything they perceive as dangerous. They avoid striking and biting because it uses up their valuable supply of venom which they need to kill and digest their food.
Rattlesnakes are often portrayed with the body partly coiled, the tail rattling loudly, and the head raised up and ready to strike, but they do not need to coil up this way to strike and bite. This display is a warning not to come any closer. It's a defensive behavior that some rattlesnakes use when they sense that crawling away would put them in danger of attack.
Rattlesnakes do not always rattle a warning. Sometimes they rattle loudly to warn potential enemies of their presence, but other times they remain silent when they sense a threat, choosing to remain still to rely on their cryptic color and pattern to let them blend into their surroundings to hide from the threat. Making a noise in this situation risks advertising their presence. They also use their natural camouflage to hunt by sitting still, without rattling, trying to remain invisible as they wait for a warm-blooded prey animal to pass close enough to strike.
Dangerously Venomous(Commonly but inaccurately called "Poisonous.")
A bite from this snake can be very dangerous without immediate medical treatment. Treatment can require hospitalization and great expense.
Adults 15 - 36 inches long, (38 - 91 cm) sometimes up to 48 inches (121 cm) with 60 inches being the longest (151 cm).
A heavy-bodied pit viper, with a thin neck, a large triangular head, and a rattle on the end of the tail consisting of loose interlocking hollow segments.
Pupils are elliptical.
Scales are keeled.
Rattlesnakes are "pit vipers" which means they have two pits that are used to sense heat when hunting warm-blooded prey - with one pit on each side of the front of the head above the mouth.
Color and Pattern
The ground color is variable, matching the environment - olive-green, gray, brown, golden, reddish brown, yellowish, or tan.
Dark brown or black blotched markings, usually with dark edges and light borders, mark the back, with corresponding blotches on the sides.
Dorsal blotches mark the front 2/3 of the body, change to dark bars on the body and dark and light rings on the tail which are well-defined and of uniform width.
The underside is pale, sometimes weakly mottled.
Usually has a light stripe extending diagonally from behind the eye to the corner of the mouth.
Young are born with a bright yellow tail with no rattle - just a single button which does not make a sound. They grow rattles and lose the yellow color as they age.
The pattern is brighter on juveniles than on adults.
Primarily nocturnal and crepuscular during periods of excessive daytime heat, but also active during daylight when the temperature is more moderate.
Not active during cooler periods in Winter.
In colder areas, known to den in burrows, caves, and rock crevices, sometimes in large numbers, and sometimes with other snake species.
Fangs and Venom
Rattlesnakes have long, hollow, movable fangs connected to venom glands. The fangs are replaced if broken. A snakes uses its fangs to inject a toxic venom which quickly immobilize its prey. A rattlesnake can control the amount of venom injected.
Bites that inject venom into humans are potentially dangerous without immediate medical treatment.
Sometimes a rattlesnake bites but does not inject venom. These are called "dry bites." A dry bite may still require medical attention.
Even a dead snake can bite and inject venom if the jaws open and close reflexively when they are touched.
A bite from any kind of rattlesnake of any age or any size should be treated as a serious medical emergency, but the bite of a juvenile rattlesnake is not more dangerous than the bite of an adult.
Experts disagree whether or not juvenile rattlesnake venom is more potent than adult rattlesnake venom, but this does not really make much difference in the severity of a bite.
While adult rattlesnakes can control the amount of venom they inject depending on their needs (small animals need less venom, a defensive or warning bite may need no venom, etc.), it is often assumed that juvenile rattlesnakes do not have the same ability and that they always inject the full amount of venom they have available. Some studies show this is not true.
There is also no proof that adult rattlesnakes are more likely than juveniles to bite without injecting venom when they are biting as a warning. Regardless of these things, adults have far more venom to inject than juveniles so the potential danger from the bite of an adult is significantly higher than the danger from the bite of a juvenile. Even when an adult does not inject the full amount of venom it has available, it most likely injects more venom than a juvenile would inject.
Sound - The Rattle
When alarmed, a rattlesnake shakes its tail back and forth. The movement rubs the rattle segments together producing a buzzing sound which serves as a warning. Juveniles are born with only a silent button at the end of the tail.
A new rattle segment is added each time the skin is shed, which can be more than one time per year.
Diet and Feeding
Eats birds, lizards, snakes, frogs, insects, and small mammals, including mice, rats, rabbits, hares, and ground squirrels.
(Adult California Ground Squirrels are immune to rattlesnake venom and will intensely confront any snake they feel to be a threat.)
Prey is found while the snake is actively moving, or by ambush, where the snake waits near lizard or rodent trails, striking at and releasing passing prey.
The snake then follows the trail of the envenomated animal and swallows it whole.
Pits on the sides of the head sense heat. These heat sensors help the snake to locate warm-blooded prey by their temperature.
Rattlesnakes are ovoviparous. The mother keeps her fertilized eggs inside her body and gives birth to living young.
Mating typically occurs in the spring. Males search extensively for females during the mating season.
Females probably start bearing young at three years of age and breed annually. (Klauber, 1982)
An average litter consists of 4 to 12 young which are born from August to October. (Stebbins & McGinnis, 2013)
Male "Combat Dance"
Adult males engage in a ritual "Combat Dance" during the spring breeding season and at other times. Throughout much of history this activity was presumed to be a mating male and female instead of two competing males. Despite the common name, it is not combat as neither male is injured. And it's not a dance, it's essentially a wrestling match in which necks and forebodies are intertwined, with the stronger snake slamming the smaller one to the ground until the weaker snake leaves the area. Most bouts end in a draw.
"Certainly the presence of a female is not necessary to stimulate males to dance."
"Dancing is not restricted to a single season of the year."
Inhabits rocky hillsides, talus slopes and outcrops, rocky stream courses, rocky areas in grasslands, mixed woodlands, montane forests, pinyon juniper, sagebrush.
This subspecies, Crotalus oreganus oreganus - Northern Pacific Rattlesnake, is found in California from Santa Barbara county, where it intergrades with the Southern Pacific Rattlesnake, east to near the crest of the Sierra Nevada, and north east of the coast and west of the Sierra Nevada and the Cascades ranges. Beyond California it continues north through Oregon, west of the Cascades Mountains in Washington and into British Columbia, Canada, and extreme northwestern Idaho.
The species Crotalus oreganus - Western Rattlesnake, occurs from Baja California north into British Colombia, throughout most of the non-desert areas west of the Rocky Mountains, excluding most of Arizona and the area west of the Cascades Mountains in Washington State.
Crotalus viridis [oreganus] has been found from sea level to around 11,000 ft. (3,350 m.) (Stebbins, 2003)
In 2010, a new elevation record for C. oreganus (lutosus) was documented at 12,112 ft. (3962 m.) Wheeler Peak, Great Basin National Park, White Pine County, Nevada. (Herpetological Review 41(1), 2010)
Notes on Taxonomy
The taxonomy of Western Rattlesnakes is controversial with several different theories. Some of these theories recommend making the three subspecies found in California full species, but this has not been widely accepted. Instead, most authorities seem to favor the split of the Western Rattlesnake species Crotalus viridis into two species - Crotalus viridis, and Crotalus oreganus.
Some authorities still use the former species name Crotalus viridis, recognizing the subspecies covered on this page as Crotalus viridis oreganus.
A study published in February 2016* used head shapes and genetic analyses to determine that there are 6 full species of western rattlesnakes found in the former Crotalus viridis complex and suggested the following names, with the three species found in California shown here at the top of the list.
If this taxonomy is accepted, the ranges and common names of western rattlesnakes found in California will remain the same, but they will be full species instead of subspecies.
* Mark A. Davis, Marlis R. Douglas, Michael L. Collyer, Michael E. Douglas. Correction: Deconstructing a Species-Complex: Geometric Morphometric and Molecular Analyses Define Species in the Western Rattlesnake (Crotalus viridis). PLOS ONE, 2016; 11 (2): e0149712 DOI: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0149712)
A 2002 study** split the Western Rattlesnake species Crotalus viridis into 7 distinct species:
Crotalus oreganus oreganus becomesCrotalus oreganus,
Crotalus oreganus helleri becomesCrotalus helleri
Crotalus oreganus lutosus becomesCrotalus lutosus. Crotalys abyssus
The common names remain the same.
** Douglas, Douglas, Schuett, Porras, & Holycross
[2002. Phylogeography of the Western Rattlesnake (Crotalus viridis) Complex, With Emphasis on the Colorado Plateau]. Pp. 11-50. In Biology of the Vipers [Schuett, Höggren, Douglas, and Greene (editors). Eagle Mountain Publishing, Eagle Mountain, Utah]
According to Todd Battey, author of SoCal Herps, an electronic field guide to the reptiles and amphibians of Southern California, Northern Pacific Rattlesnakes that occur from the Carrizo Plains south along the western side of the San Joaquin Valley differ from others of the subspecies in having a yellow dorsal coloration, a large dose of mojavetoxin in the venom, and fewer large scales between the supraoculars. This form is called the "Carrizo Yellow" form and may be distinct enough to be considered a separate subspecies pending more research.
Alternate and Previous Names (Synonyms)
Timber Rattlesnake (It is not uncommon for a rattlesnake found in a forested area in California
to be called a Timber Rattlesnake. The true Timber Rattlesnake (Crotalus horridus) is not found in California. It occurs from southeast Minnesota down to central Texas and east to northern Florida up to south-central New Hampshire.)
Mojave Green (Probably due to the green coloring on some Northern Pacific Rattlesnakes, they are sometimes called a Mojave Green, especially in the southern Sierra Nevada Mountains. The Northern Mohave Rattlesnake (aka Mojave Green) occurs only in the deserts south and east of the range of the Northern Pacific Rattlesnake.)
Stebbins, Robert C., and McGinnis, Samuel M. Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.
Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.
Samuel M. McGinnis and Robert C. Stebbins. Peterson Field Guide to Western Reptiles & Amphibians. 4th Edition. Houghton Mifflin Harcourt Publishing Company, 2018.
Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.
Behler, John L., and F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.
Powell, Robert., Joseph T. Collins, and Errol D. Hooper Jr. A Key to Amphibians and Reptiles of the Continental United States and Canada. The University Press of Kansas, 1998.
Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Snakes of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.
Bartlett, R. D. & Alan Tennant. Snakes of North America - Western Region. Gulf Publishing Co., 2000.
Brown, Philip R. A Field Guide to Snakes of California. Gulf Publishing Co., 1997.
Ernst, Carl H., Evelyn M. Ernst, & Robert M. Corker. Snakes of the United States and Canada. Smithsonian Institution Press, 2003.
Wright, Albert Hazen & Anna Allen Wright. Handbook of Snakes of the United States and Canada. Cornell University Press, 1957.
Ernst, Carl. H. Venomous Reptiles of North America. Smithsonian Institution Press, 1999.
Hayes, William K., Kent R. Beaman, Michael D. Cardwell, and Sean P. Bush, editors. The Biology of Rattlesnakes. Loma Linda University Press, 2009.
Hubbs, Brian R., & Brendan O'Connor. A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tricolor Books, 2011.
Klauber, Laurence M. Rattlesnakes. University of California Press. (Abridged from the 1956 two volume Rattlesnakes:
Their Habits, Life Histories, and Influence on Mankind.) University of California Press, 1982.
Rubio, Manny. Rattlesnake - Portrait of a Predator. Smithsonian Institution Press, 1998.
Walls, Jerry G. Rattlesnakes: Their Natural History and Care. T. F. H. Publications, Inc., 1996.
The following conservation status listings for this animal are taken from the August 2019 California Natural Diversity Database (CNDDB) Special Animals List and the CNDDB 2019 Endangered and Threatened Animals List, both of which are published by the California Department of Fish and Wildlife.
If no status is listed here, the animal is not included on either CDFW CNDDB list. This most likely indicates that there are no serious conservation concerns for the animal. To find out more about an animal's status, you can go to the NatureServe and IUCN websites to check their rankings.
This snake is not included on the Special Animals List, which indicates that there are no significant conservation concerns for it in California.