About 200 North American Eared Grebes (Podiceps nigricollis californicus) at Tule Lake Refuge in northern California were observed engaging in successive waves of mass pattering and pattering flights on 25 May 2011. Most grebes present in a part of a canal were involved in this activity. Counts of grebes on the morning of 26 May suggest an important portion of the Eared Grebes seen in pattering could have left the area over night. The behavior was characterized as zugunruhe. Directed mass pattering of Eared Grebes may contribute to synchronization of the onward migration of the birds involved.