The predator-prey relationship between California ground squirrels (Spermophilus beecheyi) and northern Pacific rattlesnakes (Crotalus viridis) is a useful system for exploring conflict and assessment. Rattlesnakes are major predators of ground squirrel pups, but pose a less significant threat to adult squirrels. Adults approach, harass, and even attack rattlesnakes in defense of their pups.
Two factors that may influence risk to both squirrel and snake during encounters are the size and body temperature of the rattlesnake. We used high-speed video to analyze the strikes of rattlesnakes of various sizes tested at different body temperatures. Results indicate that warmer snakes are more dangerous because they strike with higher velocity, greater accuracy, and less hesitation. Similarly, larger snakes are more dangerous because they can strike farther and at higher speeds, and keep their fangs embedded longer. Thus, ground squirrels would benefit from extracting information about a rattlesnake's size and temperature.
The converse of our results is that cooler, smaller rattlesnakes may be more vulnerable. These snakes could mitigate their risk by avoiding dangerous adversaries and minimizing cues that divulge their weaknesses. Such tactics might explain the active probing that squirrels direct at rattlesnakes, which may function to overcome a snake's resistance to disclosing its vulnerability.