Parent-Reared Whooping Cranes: The Impact of Different Release Methods
Photo: A juvenile Whooping Crane with one of it’s parents at the International Crane Foundation’s headquarters. Hannah Jones/International Crane Foundation
Captive-rearing programs have successfully bolstered the number of Whooping Cranes in the Eastern Migratory Population (EMP) from the initial releases of captive-reared juveniles in 2001 to the present. Within this program, adult Whooping Cranes or costumed biologists, referred to as parent-rearing and costume-rearing respectively, raise chicks in breeding facilities prior to releasing them into the EMP in the fall. However, this population has struggled with low hatching and fledging success and therefore low natural recruitment, and concerns have been raised if captive-rearing has negative long-term effects on the behavior and survivability of the EMP Whooping Cranes. Of these proposed hypotheses, this paper addresses the potential impact of release techniques on parent-reared Whooping Cranes in the wild from 2013-2019 with the objective to improve captive rearing and release strategies used today.
The fall releases of juvenile cranes are determined to be “hard” or “soft” depending on the amount of time given to acclimate to the site before official release. A hard release refers to the sudden placement of juveniles on the landscape; soft release refers to a slower process of release as juveniles are placed in a temporary pen at the release site for 2-3 weeks prior to the official release. In both protocols, juveniles were released around adult Whooping Cranes to encourage associations among the population and instill proper behaviors. From 2013-2016, soft releases were used, and parent-reared juveniles were kept in temporary pens for 1-10 days. However, from 2017-2019, all parent-reared releases were hard, and juveniles were abruptly released at the site. Other release characteristics considered each year include the location of release and availability of foraging and roosting sites, whether the cranes we are releasing juveniles near are a breeding pair or not, the number of birds released together, and the sex and age of the released bird.
From 2013-2019, 42 parent-reared juvenile Whooping Cranes were released into the EMP. All juveniles were monitored for about three weeks to document their behaviors and inform any decisions made by the Whooping Crane Eastern Partnership (WCEP). These decisions included whether we needed to intervene if juveniles were making decisions that would put them in danger, such as roosting in upland areas or spending time too close to human development. After these intensive post-release monitoring periods, the birds continued to be observed as part of a long-term monitoring program to take record of short-term survival, behavior and habitat selection, site fidelity, and associations with other Whooping Cranes. Post-release, most juveniles were observed to behave normally, including flying and roosting in water at night. On a few occasions, WCEP personnel intervened when juveniles selected upland roosting sites. As a result, the International Crane Foundation began increasing chicks’ exposure to water in captivity in 2016 and from 2017-2019 juveniles were exclusively released near water.
Many released parent-reared cranes also exhibited site fidelity and those who survived to the following spring, returned to or near their release sites in Wisconsin. Both released parent-reared and costume-reared cranes exhibited similar rates of survival one-year post-release at 69.0% and 64.4%, respectively. However, the highest risk of mortality for captive-reared Whooping Cranes was within the first 100 days post-release often due to predation or impact trauma from vehicle collisions and powerline strikes.
As a result, this study has led to several suggestions to improve the captive-rearing and release process. To improve survival, breeding facilities may consider predator aversion training for chicks to create an association of predators early on. Additionally, releasing juvenile Whooping Cranes near pairs or groups of adult whooping cranes to reinforce beneficial behaviors like predator avoidance can also improve survival. Another suggestion is to release birds in areas with fewer predators or lower densities of roads and powerlines, working with refuge partners to modify habitat at release sites to decrease risk of ambush predators as well as encouraging surrounding towns to use powerline diverters and “wildlife crossing” signs near release sites. Additional measures of public education and engagement about Whooping Cranes in their areas are also suggested to spread awareness and knowledge of the species.
While the International Crane Foundation and its partners continue to release juvenile Whooping Cranes into the EMP, our knowledge of captive rearing and its impact is growing as we implement some of these management suggestions and find opportunities to investigate others. Given the EMP is not yet self-sustaining, we will continue to depend on these annual releases to assist in their growth.
We thank Hillary Thompson, Susanna Glass, Marianne Wellington, Kim Boardman, and Glenn Olsen, the authors of the paper “Effects of Release Techniques on Parent-Reared Whooping Cranes in the Eastern Migratory Population,” for permitting us to share their work.
Story submitted by Hannah MacInnes, Crane Conservation Fellow, and Stephanie M. Schmidt, Lead Outreach Biologist, International Crane Foundation.
Reference: Thompson, H. L., M. S. Glass, M. M. Wellington, K. H. Boardman, G. H. Olsen. 2022. Effects of release techniques on parent-reared Whooping Cranes in the Eastern Migratory Population. Proceedings of The North American Crane Workshop 15:53-71.
