SOUTHERN PACIFIC RATTLESNAKE

Crotalus oreganus helleri

Geographic Distribution

Southern Santa Barbara County to northwestern Baja California, Mexico and Santa Catalina Islands.

Habitat

These rattlesnakes live in a variety of areas including grasslands, mountain forests, coastal dunes, rocky deserts and hillsides, and agricultural fields. In the northern end of their range they spend the winter hibernating in rock crevices and ledges. Many individuals (sometimes hundreds) will gather together in “snake dens” to over-winter.

Physical Characteristics

The thick body of Southern Pacific rattlesnakes ends in a short stubby tail. The rattles at the end of the tail are made up of a series of loosely jointed, dry, hollow segments of skin. Narrow ridged (keeled) scales cover the entire body. The large triangular head widens at the base. Fangs are contained in the front of the mouth. The neck is thin. Heat sensing pits are located on each side of the head. The pupils of the eyes are elliptical. The tail of young juveniles ends in a soft prebutton (an extra large scale) instead of a rattle. When the snakes shed their skin for the first time at one to two weeks after birth, another scale, the button, emerges. The button is the first segment of a rattlesnake’s rattle.

Most of these rattlesnakes blend into their surroundings due to their coloration. Although usually brown to olive-brown, they may be gray or a greenish tint. A thin brown, grey, or black stripe extends from the corner of each eye to the mouth, covers their eyes. Large, dark-rimmed spots of brown, olive, tan, grey, or black cover the back. The spots narrow into strips toward the tail. Very young snakes in this species usually have a bright yellow-green tail. Southern Pacific rattlesnakes found on Santa Catalina Island are usually almost completely black, lacking patterns.

Size

Adults are usually 75 to 100 cm (30 to 44 in) long. Some individuals grow to be over 135 cm (54 in) in length.

Diet

Rattlesnakes eat only when they are hungry. If their last meal was large, adults can go two weeks between meals. Juveniles usually eat once a week. Young snakes feed mostly on small lizards, while adults usually eat 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.)  Rattlesnakes usually are nocturnal hunters. One way that they track passing prey in the dark is by flicking their forked tongue in and out to pick up of ground odors that come from the potential meal. The smell is transmitted to organs in the roof of the mouth that connect to the brain. These snakes also catch a meal by hiding near their prey’s territory and ambushing it. Usually, one bite is enough to kill the victim before it can run or fly away.

See the Adaptation section for another way that rattlesnakes find and track prey.

Reproduction

Rattlesnakes have complex breeding behaviors. In the spring a female ready to mate releases chemicals called pheromones. Male rattlesnakes smell the pheromones and pursue the female. If two males compete for the same female, they may perform a “Combat Dance”. In this display the two males coil around each other and push up to a third of their bodies over the ground. Since the snakes have no limbs to maintain their balance, both snakes promptly topple over. This encounter can be repeated for over 30 minutes. Eventually, one snake, usually the smaller of the two, retreats. The other snake continues to look for the female. Once he finds her, he courts her by touching her with his tongue and rubbing her back with his chin.

Fertilization is internal. Unlike many snakes, most rattlesnakes are ovoviviparous. About 90 days after mating, 4-12 live, well-developed young (7 to 10 in) long are born. They are dangerous from birth as a result of being born with short fangs and the ability to inject venom. They usually stay in the area where they were born for about two weeks which is when their first molt commonly occurs and they begin forming their rattle.

Behavior

Since they are cold-blooded, rattlesnakes are only as warm or as cold as their environment. To maintain an ideal body temperature, rattlesnakes move into sunlight or shade throughout the day. By hunting and moving mostly at night, they avoid very warm daytime temperatures. Night hunting when the ambient temperature is cooler also allows their heat sensitivity to be at peak performance. Not active during cooler periods in winter.

Adaptation

All rattlesnakes are pit vipers. They have a heat receptive pit or organ between each eye and nostril covered by a thin membrane that is sensitive to infrared radiation. This sixth sense “tells” these cold-blooded snakes when their body temperature is above or below the surrounding environment. The snakes seek sunlight or shade depending on what the organs sense. Their sixth sense also enables them to “see” the heat signature of a potential prey animal or the heat trail it left behind on the ground as it ran away after being bitten by the snake. Rattlers can track their dying victim over fairly rugged terrain and comparatively long distances.

The rattle at the end of the tail of southern Pacific rattlesnakes is made up of segments of keratin. When the snakes shed their skin, a new segment of the rattle is formed.

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. The rattle warns other animals the snake is venomous and can and will defend itself. It is thought that the rattle may also prevent trampling of the snake. For example, American bison are very in tune with the particular sound of a snake rattle and will avoid it.

Rattlesnake venom is another important adaptation. The two long, hollow, hinged fangs at the front of the mouth are normally folded into a groove in the roof of the snake’s mouth. When a rattlesnake strikes, the fangs unfold snapping forward at a 45o angle. Once the fangs make contact, glands attached to the venom duct (a pathway from the venom glands to the fangs) contract, injecting the toxin. These snakes are able to control the amount of venom injected, usually injecting 20-25% of their supply at a time.

Longevity

Disease, predation, and accidents kill many rattlesnakes. As a result, many snakes only live for a few years. In protected environments, however, rattlesnakes can live between 10 and 20 years.

Conservation

Southern Pacific rattlesnakes are not listed as threatened or endangered either by the IUCN Red List or California Fish and Game. Unfortunately, due to increasing road construction and human ignorance, rattlesnakes are on the decline in almost every environment where they are found. Without these stealthy predators as a natural control, it the rodent population may increase threatening human food supplies and other wild flora and fauna.

Other than humans, rattlesnakes are commonly preyed on by birds of prey, coyotes, and Roadrunners, (Geococcyx californianus).

Amazing Facts

Much of our current-day technological advances in night-vision and heat seeking ability are a result, in part of research done on pit vipers such as the southern Pacific rattlesnake.

Southern Pacific rattlesnakes’ venom changes as they age. While the snakes are young, their venom is less potent and does not digest prey very quickly. As the snakes age and favor faster, harder to digest prey, the venom becomes stronger, adapting to the need to hunt larger and different prey to satisfy their appetites.

Rattlesnakes in California

As springtime calls people and snakes alike to the outdoors, encounters with snakes become inevitable. California has a variety of snakes, most of which are benign. The exception is California’s only native venomous snake – the rattlesnake.

California rattlesnake species include the northern Pacific rattlesnake (in northern California), and the Western Diamondback, Sidewinder, Speckled rattlesnake, Red Diamond rattlesnake, Southern Pacific, Great Basin rattlesnake and the Mojave rattlesnake (all found in Southern California). Though rattlesnakes are dangerous if provoked, they also provide humans with a tremendous service they eat rodents, other reptiles, and insects, and are in turn eaten by other predators. In California where rattlesnakes are found from sea level to the inland prairies and desert areas and to the mountains at elevations of more than 10,000 feet, enjoying the outdoors means learning how to avoid contact with rattlesnakes.

Generally not aggressive, rattlesnakes strike when threatened or deliberately provoked, but given room they will retreat. Most snake bites occur when a rattlesnake is handled or accidentally touched by someone walking or climbing. The majority of snakebites occur on the hands, feet and ankles.

Rattlesnakes can cause serious injury to humans on rare occasions. The California Poison Control Center notes that rattlesnakes account for more than 800 bites each year with one to two deaths. Most bites occur between the months of April and October when snakes and humans are most active outdoors. About 25 percent of the bites are “dry,” meaning no venom was injected, but the bites still require medical treatment.

The potential of running into a rattlesnake should not deter anyone from venturing outdoors, but there are several precautions that can be taken to lessen the chance of being bitten when out in snake country – which is just about anywhere in California.

Dos and don’ts in snake country

First, know that rattlesnakes are not confined to rural areas. They have been found near urban areas, in river or lakeside parks, and at golf courses. Be aware that startled rattlesnakes may not rattle before striking defensively. There are several safety measures that can be taken to reduce the likelihood of startling a rattlesnake.

• Never go barefoot or wear sandals when walking through wild areas. Wear hiking boots.
• When hiking, stick to well-used trails and wear over-the-ankle boots and loose-fitting long pants. Avoid tall grass, weeds and heavy underbrush where snakes may hide during the day.
• Do not step or put your hands where you cannot see, and avoid wandering around in the dark. Step ON logs and rocks, never over them, and be especially careful when climbing rocks or gathering firewood. Check out stumps or logs before sitting down, and shake out sleeping bags before use.
• Never grab “sticks” or “branches” while swimming in lakes and rivers. Rattlesnakes can swim.
• Be careful when stepping over the doorstep as well. Snakes like to crawl along the edge of buildings where they are protected on one side.
• Never hike alone. Always have someone with you who can assist in an emergency.
• Do not handle a freshly killed snake, it can still inject venom.
• Teach children early to respect snakes and to leave them alone. Children are naturally curious and will pick up snakes.

Is it a rattlesnake?

Many a useful and non-threatening snake has suffered a quick death from a frantic human who has mistakenly identified a gopher snake, garter, racer or other as a rattlesnake. This usually happens when a snake assumes an instinctual defensive position used to bluff adversaries. A gopher snake has the added unfortunate trait of imitating a rattlesnake by flattening its head and body, vibrating its tail, hissing and actually striking if approached too closely.

A rattlesnake is a heavy-bodied, blunt-tailed snake with one or more rattles on the tail. It has a triangular-shaped head, much broader at the back than at the front, and a distinct “neck” region. The rattlesnake also has openings between the nostrils and eyes, which is a heat-sensing pit. The eyes are hooded with elliptical pupils. Additional identifying characteristics include a series of dark and light bands near the tail, just before the rattles which are different from the markings on the rest of the body. Also note that rattles may not always be present, as they are often lost through breakage and are not always developed on the young.

Keeping snakes out of the yard

The best protection against rattlesnakes in the yard is a “rattlesnake proof” fence. It can be expensive and requires maintenance, however. The fence should either be solid or with mesh no larger than one-quarter inch. It should be at least three feet high with the bottom buried a few inches in the ground. Slanting your snake fence outward about a 30-degree angle will help. Vegetation should be kept away from the fence since the snake could crawl to the top of an adjacent tree or shrub. Discourage snakes by removing piles of boards or rocks around the home. Use caution when removing those piles – there may already be a snake there. Encouraging and protecting natural competitors like gopher snakes, kingsnakes and racers will reduce the rattlesnake population in the immediate area. And, kingsnakes actually kill and eat rattlesnakes.

What to do in the event of a snake bite

Though uncommon, rattlesnake bites do occur, so have a plan in place for responding to any situation. Carry a portable phone, hike with a companion who can assist in an emergency, and make sure that family or friends know where you are going and when you will be checking in.

The first thing to do if bitten is to stay calm. Generally, the most serious effect of a rattlesnake bite to an adult is local tissue damage which needs to be treated. Children, because they are smaller, are in more danger if they are bitten. Get to a doctor as soon as possible, but stay calm. Frenetic, high-speed driving places the victim at greater risk of an accident and increased heart rate. If the doctor is more than 30 minutes away, keep the bite below the heart, and then try to get to the doctor as quickly as possible.

The California Poison Control Center advises:

• Stay calm
• Wash the bite area gently with soap and water
• Remove watches, rings, etc, which may constrict swelling
• Immobilize the affected area
• Transport safely to the nearest medical facility

For more first aid information please visit California Poison Control.

References:

Aquarium of the Pacific

(aquariumofpacific.org/onlinelearningcenter/southernpacificrattlesnake)

California Department of Fish & Wildlife

(wildlife.ca.gov/News/Snake)

California Herps

(californiaherps.com)