Animals respond to stimuli by freezing in place, running away, or in the case of a change in environment, by exploring the new surroundings. Certain behaviors, such as mating or nesting, are responses to pheromone stimuli. Daylight stimulates diurnal animals to become active, while sending nocturnal creatures off to sleep.
The freezing-in-place response is typical in the young of prey species. Ducklings crouch and freeze when birds fly overhead to avoid detection. Fawns are born nearly odorless, and their dappled coats provide good camouflage as long as they stay motionless.
Prairie dogs, which live in large colonies, are examples of animals that react to danger stimuli by running and hiding. Prairie dogs take turns acting as lookouts, constantly sampling the air, listening and scanning the horizon. If a predator is spotted, an alarm cry goes out, and the entire colony heads for the safety of the underground tunnels.
Some bird species, such as the puffin, mate for life. When the birds meet at the annual nesting site, they greet each other with gestures and sounds, which stimulate the pair to prepare their nest and mate. For nocturnal creatures, such as bats, darkness stimulates them to wake up and fly out into the night sky in search of food.