The diet of G. californianus is omnivorous and varied, a good strategy for survival in the typically harsh environments of the southwest. They eat large insects, scorpions, tarantulas, centipedes, lizards, snakes, and mice. They have even been known to eat rattlesnakes, although this is rare. Greater roadrunners are potential predators of quail, adult sparrows, hummingbirds such as Anna's hummingbird, and the golden-cheeked warbler. Feeding on netted birds has also been reported. They feed on prickly pear cactus where available. When hunting they walk rapidly, scanning for prey, and then dash forward to make the catch. They may also jump into the air to catch passing insects. To kill small creatures such as rodents, greater roadrunners smash the prey's body and head against a rock and then swallow it whole. Often part of the animal is left hanging out of the mouth while it is being digested.
Animal Foods: birds; mammals; reptiles; eggs; insects; terrestrial non-insect arthropods
Plant Foods: wood, bark, or stems
Primary Diet: omnivore