Effects of release techniques on parent-reared whooping cranes in the eastern migratory population

Abstract

Reintroduction of an Eastern Migratory Population (EMP) of whooping cranes ( Grus americana ) in the United States by release of captive-reared individuals began in 2001. As of 2020, the EMP has approximately 21 breeding pairs and has had limited recruitment of wild-hatched individuals, thus captive-reared juveniles continue to be released into breeding areas in Wisconsin to maintain the population. We investigated the effects of release techniques on survival, behavior, site fidelity, and conspecific associations of 42 captive-parent-reared whooping cranes released during 2013-2019 into the EMP. Individuals were monitored intensively post-release, then as a part of a long-term monitoring program, locational, behavioral, and habitat use data were collected and analyzed. Most cranes roosted in water post-release; however, we documented 4 parent-reared cranes roosting on dry land. Most cranes eventually associated with other whooping cranes; however, juveniles released near single adult cranes were less likely to associate with other whooping cranes during their first migration or winter than juveniles released near other types of whooping crane pairs or groups. Parent-reared and costume-reared whooping cranes had similar rates of survival 1 year post-release (69.0% and 64.4%, respectively). The highest risk of mortality was within the first 100 days post-release, and the leading known causes of death were predation and impact trauma due to powerline or vehicle collisions. Both costume- and parent-reared cranes had strong fidelity to release sites. We advise releasing parent-reared cranes near pairs or groups of whooping cranes and taking measures to reduce the risk of mortality during the immediate period after release (e.g., predator aversion training, marking powerlines).