Gretchen A. Cole1, DVM; Nancy J. Thomas2, DVM, MS, DACVP; Marilyn Spalding3, DVM; Richard Stroud4, DVM, MS; Richard Urbanek5, PhD; Barry K. Hartup6, MS, DVM, PhD
1Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA; 2U.S. Geological Survey, National Wildlife Health Center, Madison, WI, USA; 3Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; 4U.S. Fish and Wildlife Service, National Wildlife Forensics Laboratory, Ashland, OR, USA; 5U.S. Fish and Wildlife Service, Necedah National Wildlife Refuge, Necedah, WI, USA; 6International Crane Foundation, Baraboo, WI, USA
In 2001, a public-private partnership began to reintroduce migratory whooping cranes (Grus americana) in the eastern United States. Cranes were costume-reared and released using one of two techniques; ultra-light aircraft-guided fall migration or direct release prior to fall migration. For the first 5 years (2001–2006), mortalities in this population (both aircraft guided and direct release birds) were documented by intensive post-release monitoring using radio and satellite telemetry. Postmortem evaluation performed on all carcasses included gross examination (forensic examination was performed when heavy metal density was detected radiographically), histopathology, and other diagnostic procedures (bacteriology, virology, parasitology, and toxicology). Choice of ancillary diagnostic tests performed was partly based on the state of decomposition and volume of remains. There were 17 mortalities of 80 released cranes (21% mortality). Known or presumed causes of death included predation (n=7), trauma (n=6), noninfectious disease (n=1), and unknown (n=3). Contributory factors, such as poor roosting habitat, intraspecific aggression, waterfowl hunting, human constructions (power lines, fences), or gunshot injury, were considered. Each of these factors was found to be significant in at least one, if not several of the mortalities of this population. Despite the intensive monitoring of all birds, pathologic examination was often limited by some degree of postmortem decomposition or scavenging. The causes of death in this migratory population were of similar proportions when compared to a nonmigratory flock of whooping cranes (Florida, USA).