Restoring Yellowstone's Trumpeter Swans

Nov 20, 2020

Brenna Cassidy, Biological Technician YNP, and Bill Long, Executive Director of Wyoming Wetlands Society, prepare to release two swan cygnets. Cygnets rely on open water to protect them from predators before they can fly.
Credit Doug Smith

Trumpeter Swans were first documented in Yellowstone National Park in the early 1900s, and they were common until the 1960s when their population started to decline. By 2010, there were only about 60 swans in the park. The loss of these birds has brought together more than seven different federal, state, and private agencies in the quest to bring them back to their former numbers.

"All kinds of wildlife are controversial," said senior wildlife biologist Doug Smith. "People like swans, and so getting that team together, although nothing's ever easy, everything costs a lot, swans certainly can cause people to come together."

The cause of their decline isn't agreed on, but according to Smith, there are likely multiple reasons.

"One school thinks it's human disturbance. People have moved into places where swans used to be successfully nesting. Another one's climate change, which has created more erratic weather in the spring. Swans don't like cool, wet springs - we're getting more of those. It's shortening the season as well. We're getting earlier ice ups, there's wetland drying, we have increased predation," said Smith.

According to Smith, the loss of cutthroat trout in Yellowstone Lake has directly affected predation by forcing bald eagles to find other food sources, like cygnets.

The cause of the swans' population decline is likely a combination of factors interacting. The park, by policy, can only address problems that are human-caused.

The reintroduction program, which started in 2011, annually releases young swans, known as cygnets, in a few areas of good habitat throughout the park. They're released just before they can fly, which helps them bond to the site. As long as they have access to open water, swans fare well in the winter and can be found in the area all year.

Lauren Walker, Wildlife Biologist for YNP, and Jennifer Carpenter, Yellowstone Center for Resources Division Chief, prepare to release two swan cygnets.
Credit Doug Smith

"If we put them out there and they flew away, they wouldn't have any bonding to that place. And we want

 them to come back to Yellowstone [and] mature. It takes them three to five years sometimes to find a territory and find a mate to live on that territory with," said Smith. "But if they're introduced to the site as a youngster - and putting them there before they can fly guarantees that they're going to stay there for a while - then they'll come back and start their life in Yellowstone, which is what we want. But they're not stuck there for the winter."

In September, eight cygnets were released. That's nearly double the number typically released. According to Smith, the number they release is determined by the number the Wyoming Wetlands Society (WWS) can produce.

WWS has semi-wild swans that they raise for reintroduction programs across the region. This is the primary source of Yellowstone's reintroduced swans.

The park will continue with cygnet reintroductions annually until there are at least four to six breeding pairs in the area. The most recent population count resulted in 21 adult swans and no young.

Have a question about this story? Contact the reporter, Ivy Engel, at iengel@uwyo.edu.