Reproductive Success of Greater Sandhill Cranes (Antigone Canadensis Tabida) at Horicon Marsh, Wisconsin

Abstract

Greater sandhill cranes (Antigone canadensis tabida) and endangered whooping cranes (Grus americana) share many life history traits. Therefore, evaluating sandhill crane productivity in certain locations could be an indicator of future whooping crane breeding success. Since 2011, captive-reared whooping cranes have been released at Horicon Marsh in Dodge County, Wisconsin, adding to the reintroduced Eastern Migratory Population. However, reproductive success of this population has remained low. Few whooping cranes spend the breeding season at Horicon Marsh, so questions remain as to whether whooping cranes can nest and raise young successfully at Horicon. To reevaluate Horicon Marsh as a release area for whooping cranes, I studied nest density and success as well as colt survival of sandhill cranes at Horicon Marsh. Fifty-seven nests were detected via aerial surveys during 2018–2019. Detection probability was estimated to be 66% using a closed-population mark-recapture method. Nest densities (0.64 nests/km2) were lower than reported in other studies. Using trail cameras, I estimated nest success of 36 sandhill crane nests. Both apparent nest success (0.82) and daily nest survival (0.991) were high compared to other published estimates. Colt survival was estimated by tracking family groups where one adult was radio marked to determine the fate of the colt(s). Colts were estimated to have a 3% chance of surviving to fledge. My results suggest that availability of nesting habitat and nest success were not limiting sandhill crane productivity at Horicon Marsh. However, colt survival may be too low to contribute to the growth of the sandhill crane population, raising questions about the potential for reproductive success for cranes of either species at Horicon Marsh.