Distribution and Abundance of Large Sandhill Cranes, Grus canadensis, Wintering in California's Central Valley

Abstract

Distribution and abundance of large sandhill cranes (Grus canadensis tabida, Greater Sandhill Crane, and Grus canadensis rowani, Canadian Sandhill Crane) were studied in California's Central Valley during October-February 1983-1984 and 1984-1985. We estimated that the population contained 6,000-6,800 cranes which were concentrated at eight geographic locations from Chico to Pixley National Wildlife Refuge (NWR) near Delano. Ninety-five percent of the population occurred in the Sacramento Valley and the northeastern Sacramento-San Joaquin Delta (S-SJ Delta); portions of the winter range varied seasonally in their importance to the population in both winters. More than half the population used the Butte Sink region in the Sacramento Valley during October-November. From December through January the Thornton and Cosumnes regions on the S-SJ Delta hosted 56-76% of the population. Sightings and locations of 157 color-marked and 10 radiotagged Greater Sandhill Cranes confirmed the movements of the population among different portions of the winter range. Most wintering sites were in private ownership, and the majority of the nocturnal roosting sites were privately owned waterfowl hunting areas. Present population estimates range from 2.5 to 2.9 times the estimates of the late 1960s and mid-1970s; differences are largely explained by variation in the effort between this and earlier studies, and the increased concentration of cranes at wintering sites in the 1980s. More than half of the wintering population may originate in coastal and interior British Columbia. Cranes originating in Canada may belong to different breeding populations than those originating in Oregon and California, although they are sympatric during the winter. Studies of the cranes from British Columbia are needed to clarify the status of the large sandhill cranes wintering in California's Central Valley.