Delineating Sandhill Crane Populations in Minnesota

Minnesota supports 2 populations of sandhill cranes (Antigone canadensis) – the Mid-continent Population that breeds and migrates through northwestern Minnesota, and the Eastern Population that breeds and migrates throughout much of the remainder of the state. Historically, there was a large area of separation between the breeding ranges of these 2 populations, with MCP and EP cranes restricted to the extreme northwestern and east-central parts of the state, respectively. Over the last 30 years, sandhill cranes have expanded their breeding distribution in Minnesota and elsewhere and are now breeding residents throughout most of the state. The population affiliation of cranes between their historical distributions is not known, however, and this uncertainty has potential implications for harvest management because MCP cranes are hunted in Minnesota, whereas EP cranes are not. We affixed GPS-cell transmitters to 50 sandhill cranes during 2014 and 2015 near the presumed boundary between breeding MCP and EP cranes in Minnesota and monitored their seasonal (i.e., migratory) and local movements to (1) determine the current range boundaries of MCP and EP cranes breeding in Minnesota and identify regions of overlap, (2) quantify habitat-use patterns, especially related use of fall staging areas in Minnesota, and (3) evaluate year-round movement patterns and annual survival of cranes breeding in Minnesota. We identified areas of overlap between breeding populations in northwestern Minnesota, near the historical range boundary of MCP cranes, suggesting that EP cranes have expanded their distribution significantly northwest. Furthermore, cranes from both populations used fall staging areas in northwestern Minnesota in the current zone where recreational harvest of MCP cranes was allowed beginning in 2010, indicating at least some overlap of populations during Minnesota’s crane hunting season. In addition, some cranes used migration routes associated with both populations, providing potential for population mixing outside of their breeding ranges. Finally, our estimates of annual survival rate of Minnesota cranes are consistent with other published estimates of crane survival rate, although because we had difficulty distinguishing mortality from transmitter failure, the uncertainty in our estimates is large. Our study provides current information about the population affiliation of Minnesota sandhill cranes, and indicates that the recent dramatic growth in abundance of cranes in Minnesota is largely a consequence of an increase in the number and distribution of EP sandhill cranes in the state. There is overlap in the distribution of these 2 populations both on the breeding grounds, and to a lesser extent, during staging, migration, and winter, potentially complicating local management options. Generally high annual survival rates likely contribute to a growing Minnesota sandhill crane population, especially EP cranes.