Spring is the period of greatest activity. Emerging from winter hibernation, they are hungry and looking for mates, as this is also the breeding season. During this time they will eat prodigiously, look for females to court, and will battle competing males. During these times of stress, and when trying to eat and when in their opaque stage several days before they are ready to shed, they are most likely to act in an aggressive manner when disturbed. Snakes migrate to and from their winter denning site, so aggregations of them may be found during a short period of time during the spring and fall.
Dens are usually in rocky outcroppings in the hills, or in deep animal burrows.
It is mistakenly believed that rattlers are active only during the heat of the day. Not only do they rest during the heat of the day, sheltered from the sun, they are adept hunters in the dark, their heat pits and sense of smell guiding them to prey. Thus rattlers are more nocturnal in summer than during the spring or fall, and adults are more nocturnal than juveniles. When out walking, hiking or camping, precautions should be taken from early morning to late evening, as temperature, season and humidity can all affect just when rattlers will be active. Despite their need for heat to be able to function, rattlers can function at surprisingly cold temperatures - especially the Mojave rattlers and sidewinders.