Winter Distribution Dynamics and Implications to a Reintroduced Population of Migratory Whooping Cranes

Abstract

Abstract From 2001 to 2012, the Whooping Crane Eastern Partnership released 196 costume-reared juvenile whooping cranes Grus americana in the eastern United States in an effort to reintroduce a migratory population of this endangered species. Techniques included leading juveniles from Wisconsin to wintering areas by ultralight aircraft or direct release of juveniles in Wisconsin prior to their first autumn migration. With few exceptions, ultralight-led cranes released on the Florida Gulf Coast wintered in inland freshwater habitats in subsequent winters. Wintering of the population occurred in four general regions: Florida–southern Georgia, coastal Carolina, the Mid-South (primarily Tennessee and northern Alabama), and the North (Indiana, Illinois, and Kentucky). Releases of ultralight-led juveniles resulted in the majority of the population returning to winter in Florida during the early years of the reintroduction. Later direct autumn releases and shortstopping by ultralight-led birds increased numbers in the Mid-South. Winter climate played a large role in wintering in the North. Drought resulted in changes in wintering locations, especially in Florida. Other factors influencing changes in distribution included habitat degradation and associations with other whooping cranes, especially new mates and birds released by different techniques. Breeding pairs and direct autumn-released birds exhibited greater winter site fidelity than did nonbreeders or ultralight aircraft-led birds, but fidelity was low for all groups. Causes of mortality differed across the winter range, with predation being most prevalent in Florida and gunshot accounting for the majority of mortalities north of Florida. Because most pairing occurred in central Wisconsin, the widespread winter distribution had no apparent negative effect on pair formation. There was no clear relationship between winter region and subsequent incubation success. The widespread distribution of the population poses minimal risk to the outcome of the reintroduction in comparison to reproduction problems in the core reintroduction area of central Wisconsin.