04 March 2008

Breeding Survey Shows Slight Decline in High Plains Swan Population

[Trumpeter Swan image from FWS survey report] James Ed. Ducey

The population of Trumpeter Swans in the High Plains flock of Nebraska and South Dakota had a successful breeding season in 2007 as shown by the annual early autumn survey results recently released by the U.S. Fish and Wildlife Service.

The 398 adults and young noted was 7% less than the number of these majestic waterfowl counted in 2006, according to the report. An aerial survey was conducted during September 4-6, 2007 by the F.W.S. and Nebraska Game and Parks Commission.

The lesser number of swans was "attributed to a decrease in nonbreeding pairs and single white birds," according to the survey report. "The majority (68%) of the pairs observed had no cygnets, and the number of white birds in groups continues to increase. This may be because many of the white birds counted have not reached breeding age or are just maturing. In 2004 a record number of cygnets were counted, and these birds are now three years old and are likely reproductively mature but may not be breeding because of limited nesting habitat. Also, many of the highest quality wetlands are occupied by pairs that nest at these locations year after year. Due to the drought conditions, such high quality breeding habitat for newly formed pairs may have been limited."

The total number of swans counted is the second highest breeding population in the region, based on results of surveys dating back to 1993, with the highest count 427 birds in 2006.

Thirty-three broods were noted during the survey, with an average of 2.33 cygnets for each adult pair.

Survey biologists noted that the number of breeding pairs was consistent, with an increase of ten, in the number of young cygnets. The number of young raised during a years' season varies from season to season, based on count results since 1993.

The distinct mix of lakes and wetlands in the Sand Hills region is especially essential habitat for this flock.

"The sandhills provide high quality wetlands with dependable water and forage, in an area that is relatively free from human disturbance," said Shilo Comeau, a FWS biologist at Lacreek NWR, who helped count the birds and prepare the report. "The majority of the nesting pairs for this flock are located in the this region and the population really began to grow once they expanded into the sandhills. If the swans had not 'discovered' the sandhills I don't believe the population would be at the level it is today."

The vast majority of the nesting area of this flock is in Cherry County within 75 miles of the refuge," Comeau said. Clubhouse, Winslow, and South Cody lakes are notable breeding locales within the sandhills. Breeding swans can usually be readily seen from a very accessible vantage point at Avocet WMA, just east of Hyannis, Nebraska.

Trumpeter Swan populations are closely monitored throughout their range in western North America.

"It is important to monitor this species to see if we are achieving the population goal set for this flock, and to monitor the overall health of the flock and its habitat," said Comeau.

Waterfowl biologists hope for an increased number of Trumpeter Swans in the interior region of the birds' range. A growth of 4.5% annually has occurred in the High Plains population since 1990, according to report details.

"Five hundred total birds is what we believe the population should be around given habitat availability and to maintain a self sustaining flock within the Interior population, Comeau said.

A survey of wintering swans is also conducted by the two agencies, during January. Results should be available by latter summer.

Trumpeter Swan Society

No comments:

Post a Comment