First, why study rattlesnakes at all? In the simplest terms, it is difficult to dispel myths and folklore without credible well-documented sources of alternative information. Indeed, a person’s own first-hand experience, no matter how extensive, is no more believable than another’s unless it is carefully documented and subjected to the timely scrutiny of others.
Many scientists have studied rattlesnakes in the past but those efforts did not include detailed investigations of the snakes’ natural history before the advent of effective radiotelemetry. Biologists knew a good deal about rattlesnake anatomy, about their venoms, and about their bites. But we knew little about how they live, how they use their venom, and how their behavior brings them into contact – and conflict – with people. But the development of miniature surgically-implantable radio transmitters with batteries that last a year or more now allow us to follow these secretive creatures around and learn where and how they live. At the same time, biochemists have been discovering that snake venoms are far more complex that we thought, often containing dozens of proteins, peptides, and enzymes – some of which are not toxic by themselves but deadly in combination. Furthermore, the structure and function of these complex toxins have turned out to be fertile ground for pharmaceutical research into potential new therapeutic drugs for humans… and knowing what the snakes eat and how they hunt and kill their prey provides clues to the physiological effects of the various venom components.
I started out radio-tracking Mohave rattlesnakes, a much-feared desert species with potent neurotoxic venom whose natural history had not been investigated in detail. Unlike Mohave rattlesnakes, other biologists have studied the natural history of northern Pacific rattlesnakes, which is the only species we have around Sacramento. But the more we learn, the more questions we have. For example, we are finding that many traits vary from population to population, including venom components, denning behavior, and reproductive frequency, just to name a few. Thus, multiple studies of different populations allow biologists to understand what traits are common and which vary from one group to another. And for those traits that vary, we want to know what causes them to vary.
Ten years ago at Loma Linda University Medical Center, we noticed that the number of snakebites in the emergency department peaked during the rattlesnakes’ courtship seasons, when females move very little while males search widely for them. Within a couple of years, we were able to show that most of these snakebites are the result of encounters with male rattlesnakes. I also had the opportunity to compare behavior of Mohave rattlesnakes during a severe drought in the desert to behavior during years with typical precipitation, producing findings that were later reinforced by northern Pacific rattlesnakes in El Dorado County. The bottom line: drought doesn’t cause rattlesnakes to wander around looking for water (e.g., drought doesn’t drive rattlesnakes into yards). They get most of their water from their prey and their greatest danger during drought is evaporative water loss. They minimize water loss by staying out of the sun and wind and remaining tightly coiled, thereby reducing exposed skin where most evaporation occurs. But because they are ambush predators, they can continue to hunt – and about 70% of the weight of each lizard or rodent eaten is water.
So why choose Effie Yeaw Nature Center for a rattlesnake study? There are two answers; first, mine: EYNC particularly interests me because the preserve is pretty much confined by the golf course and river on three sides and a densely populated residential area on the north. Since I know that the typical home range of males is large enough to challenge the boundaries of the preserve and I am keenly interested in how rattlesnake behavior creates interactions with people, I want to know how often the Effie Yeaw rattlesnakes venture into yards, as well as onto the golf course and elsewhere in the park. And I am always interested in new predatory and reproductive behavior.
Answer number two: When Denise and I found and fell in love with Effie Yeaw Nature Center, we soon became acquainted with the staff. As we shared our interest in rattlesnakes, the staff had questions. Are there only a few rattlesnakes around the Nature Center that are encountered repeatedly or are there many coming and going? Where do they spend the winter? Where do they have their babies? How often do they hide around and under the buildings?
Of course, radiotelemetry could easily answer all of those questions and more. And, at the time, I was finding my study site in El Dorado County to be less than ideal due to steep terrain, almost impenetrable chaparral, and distance from my home. I longed for an area that was closer, flatter, had fewer ticks, and less manzanita, chamise and poison oak! So Effie Yeaw Nature Center was a win-win for everyone.