JACKSON, Wyo. — A record number of trumpeter swans nested in Wyoming this year, thanks to ideal conditions and years of work by state Game and Fish Department officials to increase the numbers and distributions of swans in the state.

"All the right factors came together this year," said Susan Patla, a nongame biologist with the Game and Fish Department's Jackson office who monitors wild trumpeter swan populations for the state. "We had an exceptionally warm spring, so wetlands opened up early, allowing aquatic vegetation, (which is) the main source of food for swans, to develop quickly. Winter survival was good, and a number of new pairs, in the 3- to 5-year-old range, were ready to establish nesting territories."

Patla said in a news release that a total of 35 swan pairs occupied nest sites in northwest Wyoming. She said 20 pairs of those hatched 74 young, or cygnets. She said 59 cygnets survived until they were large enough to fly in the late fall.

That represents a 55 percent increase in number of nesting pairs and a 140 percent increase in productivity, compared with the previous 10-year averages, she said.

Game and Fish spokesman Mark Gocke said swan numbers hit a low in 1993, when only 278 swans were found in the greater Yellowstone region.

This year's fall surveys showed the total number of swans in Wyoming, Montana and Idaho was up to 498, the highest number since 1991. Gocke said swans also did well in Montana, with 41 cygnets produced, but Idaho reported only 15 young, much lower than average.

Trumpeter swans are Wyoming's rarest native nesting waterfowl species, according to Game and Fish data.

The snow-white trumpeter swan generally mates for life, normally weighs between 20 and 30 pounds, and has a wing span that stretches up to 7 feet.

Trumpeter swans went into a deep decline in the early 20th century, but considerable numbers of the birds now congregate in the greater Yellowstone area.

Major risks faced by the birds include low population numbers, low productivity and limited distribution in one of the harsher climates in the United States. Biologists said they must also compete with more than 4,000 Canadian swans that spend the winter in the Yellowstone area.

Additionally, collisions with telephone and power wires, fences and bridges is one of the highest causes of mortality for trumpeter swans.

Gocke said Wyoming's success in 2007 reflects not only the good conditions, but the success of the agency's swan expansion program. He said in the past, swans nested only in a small portion of the state, mainly in Yellowstone and Grand Teton national parks and in the Jackson Hole area.

Since 1994, the agency has been releasing captive-raised swans in the Green River Basin in western Wyoming to increase both summer and winter distribution of the bird. Swans follow their parents' movements, Gocke said, so it's difficult to get them to expand into new areas.

In 2007, the survey showed there were 11 nesting pairs in the traditional core Jackson/Snake River area and 13 in the Green River drainage. A total of 31 young were produced in the core area and 28 in the Green River expansion area.

Gocke said a pair of trumpeter swans also attempted to nest at the Alpine wetlands in the Salt River drainage.

The department is asking trumpeter swan observers to report any collared or marked swans to their local agency office. He also cautioned people about not disturbing swans while viewing the birds.