A review of the success of releases of captive-reared cranes
Cranes are among the most endangered birds in the world, with several species considered to be globally threatened. A number of crane conservation techniques exist, including legal protection, habitat protection, artificial feeding, manipulation of eggs, power line modification and captive breeding and releases. As part of a review of the relative success of these different techniques, this study provides a summary of the evidence for the effectiveness of releases of captive-reared cranes.
A literature review was conducted of the success of releases of captive-reared cranes, either into existing wild populations or as reintroductions into parts of their former range. Where possible, information on population trends, survival / mortality, breeding success and migratory behaviour were used to evaluate the success of releases.
The release of captive-reared Siberian cranes G.leucogeranus was not successful in bolstering the number of birds in the central population, with none of the individuals released seen after initiating migration (Sorokin 1995). Releases of semi-wild red-crowned cranes G.japonensis and white-naped cranes G.vipio in Khinganski Nature Reserve, south-eastern Russia, did meet with some success, with four of 10 released birds migrating successfully, and one semi-wild pair nesting successfully. At least 84% of 38 captive-reared greater sandhill crane G.canadensis tabida chicks survived for one year after release into a wild flock at Seney National Wildlife Refuge, Michigan, USA, in 1988-1990, with a minimum of 74% subsequently returning to Upper Michigan, and at least four captive-reared males nesting (Urbanek & Bookhout 1994). Captive-reared Mississippi sandhill cranes G.c.pulla had an overall first-year survival of 70% and an adult survival over 91% following release, with 60% of known breeding pairs consisting of at least one captive-reared individuals (Seal & Hereford 1992), although levels of recruitment were low. Attempts to establish a non-migratory flock of whooping cranes G. americana in Florida, USA, did meet with preliminary success, although the results of a population viability analysis suggested that population growth would be slow or negative after releases stop (Mirande & Cannon 1996).
The author concludes that although the release of captive-reared cranes shows promise as a conservation technique, it should only be used as a last resort for preserving endangered populations, and that habitat and legal protection must be in place if a reintroduced population is to become self-sustaining. Migratory releases have generally only been successful when birds were released into an existing wild flock, although the possibility of teaching captive-reared cranes a migration route (e.g. Clegg et al. 1997) is noted. The importance of monitoring birds after release to identify causes of mortality is highlighted.
Clegg K.R., Lewis J.C. & Ellis D.H. (1997) Use of ultralight aircraft for introducing migratory crane populations. Pp. 105-113 in Proceedings of the Seventh North American Crane Workshop. Baraboo, Wisconsin, USA.
Mirande C. & Cannon J. (1997) Computer simulations of possible futures for two flocks of whooping cranes. Pp. 181-197 in Proceedings of the Seventh North American Crane Workshop. Baraboo, Wisconsin, USA.
Seal U.S. & Hereford S. (1992) Mississippi sandhill crane (Grus canadensis pulla): population and habitat viability assessment workshop report. IUCN/SSC Captive Breeding Specialist Group, Apple Valley, Minnesota, USA.
Sorokin A.G. (1995) Project Sterkh: restoration of the western and central populations of the Siberian Crane, annual report 1999. All Russia Institute for Nature Conservation, Ministry of Ecology, Moscow, Russia.
Urbanek R.P. & Bookhout T.C. (1994) Performance of captive-reared cranes released into a migration route in eastern North America. Pp. 121-129 in The future of cranes and wetlands. Wild Bird Society of Japan, Tokyo, Japan.
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