A Southwestern Speckled Rattlesnake hanging out in a drainage, as it does about every morning, during the lethally hot period of Arizona summer. For much of the year, rattlesnakes are largely nocturnal, encountered by hikers and homeowners only just after sunup and again after dark.
A Western Diamondback Rattlesnake in ambush in a sandy wash on a very hot night.
This sand is much cooler than the surrounding rock, with smaller particles that lose energy more quickly. While it’s easy to think of reptiles as ectotherms always looking for sources of heat, they’re just as often looking for ways to lose it. Thermoregulating is more like a behavioral thermostat, and areas like this help.
A Western Diamondback Rattlesnake resting in partial shade. By making small adjustments to position throughout the day, a snake can precisely regulate its temperature. While they may be encountered out in full sun, this is how the majority of basking is done.
A young Mojave Rattlesnake at rest, lifted just off the surface of the warm sand to get a little air flow. Thermoregulation is far from just “sunning” – much of the activity of reptiles in the desert during the summer is about getting cooler, rather than warmer.
A Western Diamondback Rattlesnake basking in partial cover. This is how rattlesnakes and other reptiles typically thermoregulate. Filtered light and conduction from nearby surfaces and substrate can help them tune in on the right temperatures to a fine degree, all while avoiding detection by predators and prey. This is also a reminder of why it’s best to stay on established trails and keep dogs on leash when hiking in the spring.
A young Blacktailed Rattlesnake moving up from the rock wall where it lives to catch morning sun in southeastern Arizona. Structures like this provide a range of options, allowing the snake to very precisely control its temperature – warming when it needs to, and retreating to shade as the day gets hot.
