The ratio of daylight to darkness in the spring is an important zeitgeber [ˈzaɪtˌɡeɪbər] that affects the activity of some migrating birds.

zeitgeber [ˈzaɪtˌɡeɪbər]
noun

Zeitgeber refers to an environmental agent or event (such as the occurrence of light or dark) that provides the stimulus which sets or resets an organism’s biological clock.

Zeitgebers are alarm clocks—both biologically and etymologically. The word zeitgeber comes from a combination of two German terms: Zeit, meaning “time,” and Geber, which means “giver.”

English