The adult squirrels have some resistance to rattlesnake venom, which evens the odds a bit, but battles are hard-fought and can last for hours. Ronald Swaisgood, from the University of California at Davis, and colleagues, wanted to find out whether ground squirrels could assess the risk of such an encounter. Like all snakes, rattlesnakes are more active and feisty when they are warm. When they are cold, they move more slowly and will be less inclined to put up a fight.
Larger rattlesnakes are also obviously more dangerous than smaller ones.
So large, warm snakes are more dangerous and need to approached more cautiously. Fortunately, a disturbed rattlesnake gives itself away by the sound of its rattle. Even if the snake is hidden in the grass, which makes it difficult for the squirrel to judge how big it is, it can't disguise its rattle. And the sound of the rattle depends on both how large the snake is and how warm. Ground squirrels respond to a rattlesnake by waving their tails vigorously and sitting up on their hind legs in their typical confrontational posture.