In autumn the vast majority of the North American population of Eared Grebes (Podiceps nigricollis) congregates for several months at Great Salt Lake, Utah, and Mono Lake, California. Because the lakes are so large, it has not been possible to monitor grebe migration with sufficient accuracy to determine when peak numbers are reached. To clarify migration phenology, we analyzed data from 2 isolated wetland areas in southwestern Wyoming where grebes land en route between breeding areas in the interior and Great Salt Lake. Occasional birds, probably nonbreeders or failed breeders, begin moving southward as early as mid-June. Migration of postbreeding birds starts in late July, peaks in late August and September, and is largely completed by the end of October, with very small numbers arriving into November. The pattern of migration and number of birds encountered varied annually, but 95% of the migration was usually completed by 15 October. As a result, censuses at the major staging lake made on or after 15 October but before the grebes depart for wintering areas can be used to study trends in size of the North American population.
Jehl, Joseph R. Jr. and Johansson, Carl
"Autumnal migration of Eared Grebes (Podiceps nigricollis) through southwestern Wyoming: a key to assessing the size of the North American population,"
Western North American Naturalist: Vol. 62
, Article 9.
Available at: http://scholarsarchive.byu.edu/wnan/vol62/iss3/9