Wolves are the top predator in most environments in which they live and the trickle down effect of their presence is astounding. In Yellowstone, prior to the wolves' reintroduction in 1995, elk basically roamed wherever they chose and tended to spend most of their time in the river valleys. This excessive streamside grazing prevented willow and cottonwood tree growth along the river banks. But when the wolf returned, the elk quickly learned they couldn't set up permanent housekeeping in the valleys and they moved on to make a living in other areas. This, in turn, allowed young trees to grow along the riverbeds. The new trees shaded the river water, creating improved habitat for trout, which thrive in cooler, darker waters. The new willows and cottonwoods attract additional migratory birds and provided new food sources and building materials for beavers. The beavers then built dams which created new marshes and wetlands that in turn attracted otters, ducks and other species. Wolves provide tremendous economic benefits. Ecotourism is quickly moving to the forefront of family recreational activities. The longing to see animals in their natural habitat has created an economic boom throughout the United States. In Yellowstone, fishing has always been a big industry and the improved environment along the river caused by the wolf's presence has improved fishing opportunities. The wolves themselves are also a huge tourist draw, with many people making Yellowstone their vacation destination expressly for the purpose of seeing wolves. Indeed, most sunrises in Yellowstone are accompanied by rows and rows of nature lovers with spotting scopes, all straining for a glimpse of the elusive wolf. Wolves pose little threat to livestock and humans. In fact, their prey of choice has been wild game like deer and elk for centuries. The same is true for human/wolf interactions. Despite claims by wolf opponents, the fact remains that aggression by wolves against humans is a very rare event.