Ornithologists have noted that especially during the winter, American Crows assign one or more of their flock to keep watch over the rest of the group, or “murder,” as they feed on the ground nearby. While acting as sentinels, the crows will call frequently, even when predators are not present. When they intensify their calling, the crows that are feeding often flush.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.