STATUS, PRODUCTION AND MIGRATIONOF GREATER SANDHILL CRANES ON AGASSIZNATIONAL WILDLIFE REFUGE, MINNESOTA

Greater sandhill cranes (Crus canadensis tabida) nesting at Agassiz National Wildlife Refuge (NWR) in northwestern Minnesota were studied from 20 April 1984 to 10 December 1985. Local birds were monitored to determine population size and age structure, reproductive success, and migration routes and wintering grounds. Forty-two pairs were identified. Thirty-four were breeding pairs and 3 were subadult (nonbreeding) pairs. Twenty nests were found; pairs at 13 of these hatched at least 1 young. Forty-three pairs hatched a minimum of 62 young, and 28 pairs fledged 42 of 47 young. Fifteen birds were colormarked, 8 of which were radio-tagged and followed through parts of their migration. Unlike cranes nesting in eastcentral Minnesota, these birds entered the Central Flyway. One bird was traced to east Texas wintering grounds. Once found throughout Minnesota, exclusive of the northeast (Johnson 1976a), greater sandhill cranes presently exist as 2 separate breeding populations within the state, one in the northwest, the other in eastcentral Minnesota. Both populations have expanded in recent years and the separation between them has become less distinct. Migrating cranes are also seen in Minnesota at traditional migration staging areas in northwestern and westcentral parts of the state. A history of nesting sandhill cranes in Minnesota has been provided by Johnson (1976a), and accounts of their status and distribution have been given by Johnson (1976a), Grewe (1977), D. Murphy (Prelim. Rept. Sandhill Cranes in northwestern Minn., St. Cloud State Univ., St. Cloud, Minn., 1978), and C.L. Henderson (Minn. Sandhill Crane Rept., Minn. Dept. Nat. Resour., St. Paul, 1979). Most recently, the eastcentral population has been estimated at 87-109 pairs, and the northwest population at 760-1160 pairs (M. C. Tacha & T. C. Tacha, Status and Distribution of Sandhill Cranes in Minn., Minn. Dept. Nat. Resour., St. Paul, 1985). Data on the ecology of summering cranes in Minnesota are limited. Johnson (1976b) studied the biology of nesting cranes in the eastcentral population. Crete & Toepfer (1978) determined the migration route and wintering grounds of this population, demonstrating their affiliation with the eastProc. 1988 N. Am. Crane Workshop ern (Great Lakes) population of greater sandhill cranes. The affiliation of the northwest population has been less certain. The close proximity of the 2 populations could suggest that these birds are also a part of the eastern population, as has generally been assumed. This idea was supported by the sighting of 2 color-marked birds in Manitoba, and another in western Minnesota, that had previously been marked on Florida wintering grounds (Nesbitt & Williams 1979). Conversely, there has been evidence to suggest that these birds are more accurately associated with the mid-continent population of sandhill cranes (includes G. c. rowani and G. c. canadensis). When tabida was first identified on east Texas wintering grounds, it was suggested that they may have corne from sou theas tern Manitoba and northern Minnesota (Lewis 1974). Melvin & Temple (1980) later demonstrated that sandhill cranes from the Interlake Region of Manitoba do, in fact, migrate through the Central Flyway to winter along the Texas coast. However, the subspecific designation of those birds is not certain (Lewis 1977). The presence of the Canadian subspecies (G. c. rowani) in migrant flocks in Kittson County, Minnesota (Johnson & Stewart 1973), led Johnson (1976a) to suggest that local cranes in northwestern Minnesota would be unlikely to separate from migrant flocks 1 Present address: Minnesota Department of Natural Resources, Wetland Wildlife Populations and Research Croup, Bemidji, MN 56601