The young timber rattlesnake, coiled and camouflaged beside a log in Washington University's Tyson Research Center near Eureka, Mo., offers a steely stare. He doesn't give up his position with a rattle or a tongue flicker. And he can't blink.

For sheer cold-blooded indifference, rattlesnakes are unrivaled. They can remain motionless for days. But track 28 of the venomous pit vipers for six years, as Washington University researchers have, and the snakes reveal slightly more flamboyant behavior.

They swim. They climb trees. Some males travel more than six miles a year in search of mates. One snake caught rainwater in its funnel-shaped coil and drank from its own cup.

The snakes' paths suggest they can live in more than just forested areas - something that offers hope to biologists who have seen the rattlers' population decline over the last century. The snakes seem to prefer habitat ''edges,'' the boundary zones between a forest and a road or a crop field.

''Edges aren't all that bad,'' said Corey Anderson, a doctoral student in biology. ''Timber rattlesnakes are thought of as these sensitive, secret creatures. But it may be that some snakes can coexist with anthropogenic habitat. It'd be shocking to people if they knew how many den locations I have along I-44.''

The snakes might be able to live amid people, but the reverse generally hasn't been true. Some states offered bounties for severed tails into the 1980s.

Yet the snakes haven't posed much of a threat to humans. There were 1,245 rattlesnake bites reported to the American Association of Poison Control Centers in 2003, but only one death. That compares to the 44 people who died from lightning strikes in 2003, according to the National Weather Service.

The snakes are an important control on squirrel and mouse populations. But many people can't separate the snakes from the connotations of their Latin name, Crotalus horridus.

Maybe that's why Wayne Drda gives them cuter names, like Groucho, Abraham and Lucyfer.

Drda, a wiry 65-year-old, wields an antenna on a forested hilltop. He's listening for the beep of a radio transmitter embedded in the body cavity of Yanni, a 4 1/2 -foot-long rattler.

Veterinarians place the pinkie-sized transmitter in the snakes' body cavities after the researchers catch them - usually with a U-shaped tong and plastic buckets. The transmitters, finally small and cheap enough ($300), have revolutionized the study of snakes, long considered elusive.

Plumping up the preserve: The researchers have no way of knowing the total snake population at Tyson. Drda guesses there are about 200 adults in the 2,000-acre preserve.

After a career as a chemical engineer and schoolteacher, Drda volunteers as a researcher. He refers to the rattlesnakes almost like children. Drda fondly recalled the way Yanni digested a squirrel.

''When he got that bolus down, wow, he wanted to move,'' Drda said. ''That's such wonderful feeding area, you just watch them plumping up out there.''

The beeps get louder. Ryan Turnquist, 18, another research assistant, knows he's close. He freezes and scans the ground intently. He's well-practiced in spotting snakes: He has caught and raised eight snakes at home and has received science fair honors for his work with snakes. Drda has a breeding colony of 35 bull snakes at his home.

''They're herp kids,'' said Anderson, referring to herpetology, the study of snakes. ''Maybe their moms didn't let them have a dog.''

They soon find Yanni lounging in some leaves, shaded by sumac plants. Drda aims an infrared spot at the snake's head and measures its temperature. Anderson leans over to record Yanni's location with a Global Positioning System unit.

Yanni doesn't react at all.

''He's laid back - he just likes to lay in the leaves,'' Turnquist said. ''He kind of knows nobody will mess with him - he's so big.''

Living on the edge: At the Washington University biology department, Anderson analyzes the snakes' annual paths, from the time they emerge from dens in April to their hibernation in October.

He found that the snakes followed similar paths year after year - navigating by scent, perhaps. He also noticed the snakes avoided the vast wooded interior of the research center. Many instead clustered near the Meramec River flood plain or in an area along Interstate 44.

For example, Ingrid, a female, patrolled a narrow swath of land between a fence and I-44 - even though Anderson says it's a ''junky'' habitat full of honeysuckle vines, cedar trees and garlic mustard.

''It's almost like the snakes prefer not to use the woodlands,'' he said.

The edge habitat has two advantages, said Chris Phillips, a herpetologist with the Illinois Natural History Survey. There are more sources of food along edges. And there are more ways for the cold-blooded snakes to thermally regulate - to bounce back and forth from sun to shade.

But in the case of roads or crop fields, there are also more chances for a snake to get killed.

Phillips says biologists agree timber rattlesnake populations are declining. From 1880 to 1980, there were at least 100 rattlesnake sites along the Mississippi River between Missouri and the Wisconsin border, Phillips said. Now, there are only a half-dozen sites.

Nationwide, the rattlers exist in 30 states. They've disappeared from Canada, Maine, Rhode Island and Delaware. Thirteen states list the timber rattlesnake as threatened or endangered.

That's why Phillips is frustrated by hikers who say they're scared after learning Phillips studies rattlesnakes there. The snakes are both scarce and bashful. Phillips has a staff that searches 12 hours a day for rattlesnakes to track. They often return empty-handed.

''It would be the ultimate thrill to see one because it is such a rare event,'' he said.

Washington University researcher Wayne Drda uses an antenna to locate a receiver embedded in Paco, a timber rattlesnake in the Tyson Research Center in Eureka, Mo. Scientists use the data to learn about the snakes' range of travel and breeding habits.