Status and Harvests of Sandhill Cranes: Mid-continent and Rocky Mountain Populations

The MCP (Mid-Continent Population) of sandhill cranes, the largest of all North American crane populations, is comprised of about two-thirds lesser (Grus canadensis canadensis), one-fourth Canadian (G. c. rowani), and the remainder greater (G. c. tabida) sandhill cranes. Collectively this population was believed to number over one-half million during the decade of the 1990's (Tacha, et al.1994). The breeding range extends from northwestern Minnesota northeastward into western Quebec, then northwest through Arctic Canada, Alaska, and into eastern Siberia. The MCP wintering range includes western Oklahoma, New Mexico, southeastern Arizona, Texas, and Mexico south to near Mexico City. Extensive aerial spring surveys, corrected for observer visibility bias on major concentration areas, provide annual indices of abundance used to depict population trends. These surveys are conducted in late March, when birds that wintered in Mexico, Arizona, New Mexico, and Texas usually have migrated northward to spring staging areas, but before spring "break-up" conditions allow cranes to move into Canada (Benning and Johnson 1987). The MCP Cooperative Flyway Management Plan establishes regulatory thresholds for changing harvest regulations, which are based on an objective of maintaining sandhill crane abundances at 1982-2005 levels. Hunters are required to obtain either a Federal crane hunting permit or register under the Harvest Information Program (HIP) to hunt MCP cranes in the U. S. The permits or HIP registration records provide the sampling frame to conduct annual harvest surveys. In Canada, the harvest survey is based on the sales of Federal Migratory Bird Hunting Permits, which are required for all crane hunters. The RMP (Rocky Mountain Population) is comprised exclusively of greater sandhill cranes that breed in isolated, wellwatered river valleys, marshes, and meadows of the U. S. portions of the Central and Pacific Flyways (Drewien and Bizeau 1974). The largest recorded nesting concentrations are located in western Montana and Wyoming, eastern Idaho, northern Utah, and northwestern Colorado. The RMP migrates through the San Luis Valley (SLV), Colorado and winters primarily in the Rio Grande Valley, New Mexico (with smaller numbers that winter in the southwestern part of that state), in southeastern Arizona, and at several (14) locations in the Northern Highlands of Mexico. During 1984-96, the RMP was monitored at a spring stopover site in the SLV. However, cranes from the MCP also began to use this area, which confounded estimates of RMP abundance. In 1996, a fall pre-migration (September) survey replaced the spring count as the primary tool for monitoring population change. The RMP Cooperative Flyway Management plan established population objectives, a survey to monitor recruitment, and harvest levels that are designed to maintain a stable abundance between 17,000-21,000 birds (Pacific and Central Flyway Councils 1997). The plan contains a formula for calculating allowable annual harvests to achieve population objectives. All sandhill crane hunters in the range of the RMP must obtain a state permit to hunt cranes, which provides the sampling frame for independent state harvest estimates and allows for assignment of harvest quotas by state. In many areas, harvest estimates are supplemented by mandatory check-station reporting.