The marshes and lakes throughout the northern United States and Canada were once inhabited with great numbers of trumpeter swans (Cygnus cygnus buccinator). Due to large-scale hunting in the 1700s and 1800s, the species became severely endangered and disappeared as a nesting bird throughout much of its range. For example, by the mid-1900s, only 69 swans remained in Wyoming, Idaho, and Montana and, prior to 1987, it had been one hundred years since a pair of trumpeters reproduced in Wisconsin. The Milwaukee County Zoological Gardens, the Zoological Society of Milwaukee County, and the Wisconsin Department of Natural Resources (DNR) are working cooperatively with the U.S. Fish and Wildlife Service (FWS) and others to return trumpeter swans to at least a portion of their former breeding range.
The goal of the Wisconsin Trumpeter Swan Recovery Program, which began in 1987, is to restore a breeding and migrating population of at least 20 pairs of trumpeter swans to Wisconsin by the year 2000. The Bureau of Endangered Resources within the Wisconsin DNR provides overall administration and coordination of the program, while the Milwaukee County Zoological Gardens and the Zoological Society of Milwaukee County play essential roles in egg collection, captive breeding and release of swans.
Wisconsin DNR personnel fly to Alaska annually to collect trumpeter swan eggs for the program from the healthier Alaskan populations. In accordance with the FWS guidelines for egg removal, at least two viable eggs are left in each nest visited and eggs are collected from a different region each year to ensure genetic variation. The eggs are carefully transported to Milwaukee County Zoo for hatching in special incubators. Newly hatched cygnets are then reared and reintroduced by one of two techniques: decoy rearing or brooder rearing. Cygnets that are decoy reared are transferred from the incubators to a specially designed imprinting/rearing area and isolated from human contact. The cygnets are introduced to a life-sized trumpeter swan decoy and for three to seven days the cygnets learn to follow the decoy parent to food and away from danger as it is manipulated by zoo staff hidden behind visual barriers. From a speaker in the decoy the cygnets are exposed to swan calls appropriate to different situations. After this brief imprinting period at the zoo, the swans are taken to selected reintroduction sites in northern Wisconsin marshes. Interns, funded by the Zoological Society of Milwaukee County and supervised by the Wisconsin DNR, are disguised at the site on camouflaged floats. From these floats, the interns carefully tow the parent decoy through the water, leading the cygnets to food and demonstrating with the decoy¹s movable head and neck how to retrieve it. The swans are attended daily until the ice of winter forces their migration and release.
Brooder rearing is an entirely different technique. Cygnets reared in this manner are transferred from the incubators to a "brooder box." To discourage imprinting on humans, zoo keepers cover themselves in neutral colored gowns and do not speak when working in the brooder area. After five to six weeks, the cygnets are transferred from the Zoo to an "overwintering" lake site where they are protected and closely monitored, but again strictly isolated from their human caretakers. After two years at the site, when they are ready to begin nesting, the swans are paired and released on selected marshes.
All released swans are banded and collared for monitoring. These data are critical for gauging progress and for evaluating the effectiveness of the two captive rearing and reintroduction techniques. To prevent accidental shooting of reintroduced swans, the DNR educates hunters in the area about the identification of swans and goals of the program. In addition, both the Milwaukee County Zoo and the DNR distribute educational materials to diverse audiences and conduct lectures to promote this conservation effort.
The program has demonstrated great success, attracting support from a diverse coalition of public and private institutions including zoos. The Lincoln Park Zoological Gardens supports the current AZA Trumpeter Swan Studbook keeper; the Minnesota Zoo participates in a captive-release program with the state of Iowa; and the state of Ohio is beginning a program modeled after the Wisconsin program. Currently, 18 nesting pairs of trumpeter swans in Wisconsin originated from the captive release program and a total of 255 trumpeter swans have been released into the wild. There have been 25 cygnets produced from released pairs. The Milwaukee County Zoo hatched 48 out of 51 eggs this year. Participants are confident that they will meet the goal of establishing at least 20 breeding and migrating pairs by the year 2000. (Excerpted from Julia Bowdoin, AZA Communiqué October 1994 and personal communication, Kim Smith, Milwaukee County Zoological Garden.)
For more information, contact:
Kim Smith, Milwaukee County Zoo, 10001 West Bluemound Road, Milwaukee, WI 53226; Tel: (414) 256-5457; Fax: (414) 256-5450.
Ed Diebold, Riverbanks Zoological park and Botanical Gardens, P.O. Box 1060, Columbia, SC 29202.
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