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LARGE SANDHILL CRANES WINTERING IN CALIFORNIA 269 eral public during this period seeking informa- complementary(i.e., one from each site contain- tion on the distribution of cranes. We partici- Ing cranes) counts/region to calculate regional pated in five aerial surveys of the Sacramento population estimates for each month. We se- Valley and the S-SJ Delta between October 1983 lected the series of counts included in each re- and February 1985. We also investigated the oc- gional population estimate to minimize the prob- currence of cranes beyond the limits of the in- ability of counting the same individuals at more tensive study areas to delineate the boundaries than one site. Roost counts and daytime counts of the population's distribution. The Central were not conducted in the same regions to avoid I Valley is also the principal wintering area of the counting individuals at more than one site. The Pacific Flyway Population of Lesser Sandhill series of counts in each region were always com- Cranes (Littlefield and Thompson 1982); there- pleted within 1-7 days. The chronology of the fore, we attempted to visit all locations from counts which were summed to estimate the pop- i which we received reports of any cranes to de- ulation's size are presented in Table 1. I When conductIn counts in regions with both termine subspecific composition. g g' i Lesser and Greater Sandhill Cranes, we distin- ABUNDANCEguished Lesser Sandhill Cranes by their small We estimated the size of the Central Valley Pop- body size, high pitched calls, active demeanor, ' ulation by conducting monthly censuses during shape of their heads,the length and shape oftheir October 1983—January 1984. Complementary bills, and the length of their bills relative to the 1 !� sets of counts from each region were selected and size of their heads(Fig. 2). At some locations we l summed to estimate the size of the population noted the presence of cranes which appeared in- for each month (see below). termediate the size between Greater and Lesser i Our objective was to obtain complete counts Sandhill Cranes. These intermediate-sized birds I in each region in as short a period of time as resembled Canadian Sandhill Cranes, G. c. ro- possible to avoid duplicate counting'of individ- wani (Walkinshaw 1965), which probably orig- uals which moved between sites. To accomplish inated in British Columbia (Littlefield and this objective we identified important sites used Thompson 1979, U.S.F.W.S. 1983, Campbell et by cranes and then conducted a series ofcensuses al., 1990). We included the intermediate cranes at all sites which simultaneously hosted cranes. in the estimates of the size of the Central Valley We censused two sites simultaneously whenever Population because they were distinguishable } possible and conducted censuses at additional from Lesser Sandhill Cranes but were not con- ;1 sites on successive days to obtain a complete sistently distinguishable from Greater Sandhill count from each region. Cranes. Thus, our population estimates repre- To census individuals we counted flying cranes sent the number of "large cranes" (including �. at dawn as they left roost sites, or when they Greater and Canadian Sandhill Cranes), present returned to these roosts in the evening. During on the winter grounds in the Central Valley.This these counts we scanned flocks of cranes with approach is consistent with the definition of the binoculars, individually counted the birds in Central Valley Population in the Pacific Flyway flight, and recorded the number of individuals Management Plan (U.S.F.W.S. 1983). } with multiple-field tally meters. We conducted j the roost counts from platforms 1.5-2.0 m high MARKED CRANES constructed over the beds of pickup trucks or To describe population movements, verify our from vantage points which permitted unob- assumptions about distribution, and find addi- +ltl structed views. We also conducted roadside sur- tional wintering sites used by the population, we int veys during mid-day in areas where cranes were observed color-marked and radio-tagged cranes. dispersed and where roost counts were an inef- Between 1966 and 1984,345 cranes were marked ficient method for estimating the number of in- at Malheur NWR, an important nesting and fall �t dividuals present. We conducted 71 dawn and staging area(Littlefield 1986)in southeastern Or- dusk roost censuses at 21 difFerent sites, 33 dur- egon. In 1983 and 1984, 39 cranes were marked Ing morning flights and 38 in the evening; and at Sycan Marsh, a nesting area in southcentral 44 daytime censuses at 24 different sites in all Oregon, and in 1984, eight cranes were marked four months. After completing a series of counts at Modoc NWR, a nesting area in northeastern in each region, we selected and summed 1-6 California. t t VI-129 �r=