Bringing the Wolf Back to Yellowstone
Returning the Wolves is Helping Balance the Yellowstone Ecosystem
Jul 14, 2009
Yellowstone National Park was established in 1872, mainly to preserve its geologic wonders--geysers, hot springs, colorful mud pots and spectacular canyons and waterfalls--for tourists. But park visitors also enjoyed the wildlife such as elk and deer, but they didn't appreciate the predators that hunted these animals, especially wolves. This attitude resulted in the wholesale slaughter of the Yellowstone wolves. By 1926, the wolves were all gone.
After the Wolves Were Gone, Elk Increased in Population
Safe from the wolves, elk became more numerous in the park as the years passed. When winters were mild, many elk survived, and without wolves to keep the population down, elk numbers swelled. Park rangers stepped in to control elk numbers. They trapped the elk and sent them to other parks and preserves, but sometimes they had to shoot hundreds of them to keep the population down.
The elk became complacent, hanging out in the shade of trees along the creeks and rivers and eating the tender shoots of young willows and aspen. These trees have a short life span, and before long, few young trees grew to replace the old ones.
Fewer willows and aspen meant fewer beavers, which use these trees for food and building materials for their lodges and dams. Since beaver ponds, with their surrounding trees, provide habitat for a great variety of birds, fish, frogs, and other living things, these, too, became less common in the park.
Too Many Coyotes
Without wolves, their smaller cousins, the coyotes, became more numerous. Coyotes feed on everything from elk calves to insects. But they eat mostly small rodents such as ground squirrels. With too many coyotes, life became harder for other small predators like foxes and badgers.
Another favorite food of coyotes is fawns of the pronghorn, an animal unique to North America. As the years went by, scientists wondered if the decline of the pronghorn population in Yellowstone was at least partly due to coyote predation on the fawns.
Consequences of Bringing Back the Wolf
As they learned more about the interconnections in nature among the animals and plants, ecologists and wildlife managers realized that Yellowstone needed wolves in order to provide a healthy, more complete ecosystem.
After years of political battling, wolves trapped in Canada were transported to the park and released in 1995 and 1996. They were kept in large pens at first to get them used to their new home. Once they were free, the wolves thrived and multiplied, and scientists began seeing positive changes in the ecosystem.
The wolves kept the elk on the move, so they can't hang out along the streams and rivers. The aspen and willows began growing back, and now more beaver have made their homes in the park. Thus the birds and other wildlife that depend on the ponds are returning, too.
The wolves killed and chased away many of the coyotes, giving the other small predators a better chance of survival. The pronghorn population also seem to be doing better now with fewer coyotes as well.
Even the grizzly bears seem to be benefiting from wolf return. When grizzlies leave their winter dens in the spring, they need to eat quality protein. Grizzlies are much bigger than wolves and can bully them away from their kills, providing the grizzlies with what they need to regain their strength in the springtime.
Lessons for Ecosystems Everywhere
The apparent improvements in how the Yellowstone ecosystem functions since wolves were returned show just how interconnected all the elements of an ecosystem are. Remove one piece, especially a major piece like a top predator, and unforeseen problems can develop. Fortunately, returning that piece of the puzzle can help heal the system.
References
Patent, D.H. (2008) When the Wolves Returned: Restoring Nature's Balance in Yellowstone
Smith, D.W. and G. Ferguson (2005) Decade of the Wolf: Returning the Wild to Yellowstone
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