Here's a little info on the Prairie Rattler that you could run across in South Dakota hunting Pheasants.
http://www.sdsnake.com/Rat.htm
The color of the Prairie Rattlesnake varies from light brown to green, with a yellowish belly. Dark oval blotches with light colored borders run along the center of its back. The blotches become crossbands on the back part of the body and rings around the tail. Adults will range in length from 30-40 inches, with a record of 57 inches. 3 foot rattlesnakes normally weigh 1 pound (a 54 incher weighed 4 1/2 pounds).
Many South Dakotans admit they have never seen a rattlesnake in the wild, even those in rattlesnake country. If they knew how many times they where within 10-15 feet of a snake, there would be many places they would never go back to. Use your mouse and click on this graphic to see if you can see the snake. The snakes are there; if you leave them alone, they will likely do the same to you. If you did not find the snake, click on this rattlesnake graphic to see the location of the snake lying outstreched in the grass. As seen with my graphic, snakes have a great display of camouflage. Most snakes are normally timid and secretive. When approached, they usually remain quiet to avoid detection. They may try to escape if given an opportunity. When frightened, cornered, or attacked, snakes will stand their ground and may attempt to strike at or bite their intruder.
There was an interesting article in the South Dakota Magazine (September/October 1991) "Rattlesnake Hunt at Mobridge". Several men went snake hunting on a prairie dog town on a warm fall afternoon. When the hunt was over, the men had killed over 400 rattlesnakes at this denning area. Most dens will average 250 snakes, but some dens have been reported to have up to 1,000 snakes of the different species, denning in the underground structure.
Rattlesnakes are cold-blooded or ectothermic animals. Their body temperature is influenced more by the temperature at the grounds surface where they are lying, rather than the air temperature. High or low temperatures cause the snakes to seek escape cover or shady areas. Most snakes cannot survive exposure to direct sunlight with temperatures over 100 degrees F, but rattlesnakes have a greater endurance to lower or freezing temperatures. Lethal temperatures for the snakes depend on the time of exposure. Unlike warm-blooded or endothermic animals, snakes are unable to produce their own body heat. To maintain a desirable temperature, snakes must rely the temperature or warmth of their surroundings. The snake's circulatory/nervous systems aid in controlling the warming or cooling of their body.
With the harsh winter conditions in the northern states, rattlesnakes need to find an underground refuge for the winter months. Early fall frosts and shortening daylight, encourage snakes to move toward the dens, normally found on hillsides, bluffs, and rocky outcrops with underground openings used as denning sites. Snakes will also den up in holes or burrow systems of prairie dogs or other animals. Any such underground hole, crevice, mammal burrow, or other retreat area must be deep and extend to a depth below the frost line. The dens are normally found on hillsides with a southerly sun exposure allowing for spring and fall basking in the sun. Preferred dens are found on higher elevations above creeks and drainages that may be prone to spring flooding. Snakes cannot dig their own holes, although they can push or root out material with their noses. Vacant holes left behind by other animals are often used as escape cover or denning over the winter months. The first freezing temperatures in the fall months, snakes start their movements toward the den and will congregate near the den until the lower temperatures drive them underground. In the late March or April, triggered by increasing ground temperatures, the snakes will move toward the ground surface or the den opening. With the warming nighttime temperatures and the prolonged period of sunlight, snakes leave the den to find food, mate, and have young during their summer travels. Throughout the summer months, the dens are abandoned and the snakes will travel 2-4 miles from their den. In a Wyoming study, radio transmitters were implanted in various snakes and one female rattlesnake traveled a distance of 8 miles from its den. Snakes return to the same den year after year, provided the den is not disturbed or destroyed. These dens or hibernaculums have been used by many generations of snakes over the years. Some people feel that snakes leave scent trails or pheromes to identify past travels. Other snakes, such as juveniles, may use their sense of smell to follow the odor or pheromes trails of adult snakes, to locate their dens.