Since the Santa Catalina Rattlesnake lives mainly in trees, scientist first thought this rattlesnake eats birds, but scientist have now found out that around 70% of the Santa Catalina Rattlesnake's diet is made up of small mammals like the Santa Catalina Deer Mouse, and around 30% is made up of lizards like the Santa Catalina Desert Iguana and the Santa Catalina Side-blotched lizard.