EarthWord: Crepuscular

Release Date:

The term crepuscular describes events relating to, resembling, or occurring during twilight, meaning morning and evening hours. An animal described as crepuscular is active during twilight.

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USGS scientists prepare to launch the Raven-A sUAS at the start of civil twilight. Credit: USGS Fort Collins Science Center
USGS scientists prepare to launch the Raven-A sUAS at the start of civil twilight. Credit: USGS Fort Collins Science Center

Definition:

  • The term crepuscular describes events relating to, resembling, or occurring during twilight, meaning morning and evening hours.  An animal described as crepuscular is active during twilight.

Etymology:

  • Comes from the Latin word creper, meaning “dark.”

Use/Significance in the Science Community:

  • Many different species of birds, mammals, and a variety of other animal species are crepuscular, and knowing when a species is active is fundamental to studying its behavior and abundance, and in making many other observations.

USGS Use:

  • USGS researchers refer to grizzly bears in the Greater Yellowstone Ecosystem as having crepuscular peaks in activity because they tend to be more active during twilight hours in the morning and again in the evening.  Their crepuscular peaks are most pronounced during the hot summer months of June-August.  In a recent study conducted in Yellowstone National Park, scientists discovered that grizzly “bear-jams,” roadside bear viewing opportunities that cause traffic congestion in Yellowstone National Park during the summer, are related to the tendency of bears to be crepuscular.  
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