Animal Behavior: Orientation and Navigation

A Zeitgeber is an environmental agent (such as light or temperature) that entrains an individual's behavior to that environment. Zeitgeber is German for "time-giver".

An endogenous stimulus comes from within the body of an animal. An exogenous comes from the external environment of the animal.

Behaviors based on a daily cycle are called circadian. Month-based behaviors are called lunar and year-based behaviors are called circannual.

Common circadian zeitgebers include sun and starlight. Lunar behaviors are often timed to tides. Circannual behaviors can be timed to seasonal temperature differences and the length of the day.