Killing wild animals doesn't seem so eco-friendly at first.

History shows us that hunters were the ones who decimated the bison population across North America and made the passenger pigeon extinct. Lead ammunition left behind after a hunt can cause waterfowl to become sick.

And in many cases, the hunting of predator species such as grizzly bears and wolves has left prey species dangerously overpopulated.

According to the U.S. Fish and Wildlife Service, there were more than 12.5 million active hunters over the age of 16 in the United States as of 2006. They definitely have to have a large impact on the environment -- but that is not necessarily a bad thing.

"Hunters are the most conservation-friendly people out there. They are good stewards of the environment," said Joe Hosmer, vice president of the Safari Club International, a foundation recognized as a worldwide leader in wildlife-conservation and education programs.

And some environmentalists agree.

"Done properly, with proper regulation and wildlife management, hunting can be very 'green,'" says Douglas Inkley, a wildlife biologist who holds the position of senior scientist at the National Wildlife Federation.

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"Once regulations and proper management were in place here in the United States, hunters have never made a game species extinct, endangered or even threatened," says Hosmer. "Wildlife management is done scientifically and with laws to prevent this from happening."

Hunters hunted 220 million days and took 185 million trips in 2006. They rely on varied wildlife populations remaining strong from one generation to the next, so there will always be game. This wildlife, in turn, requires a diverse natural habitat that is unpolluted and undisturbed.

"Preserving land not only helps the hunted species, but benefits all other species living in and around this land," added the National Wildlife Federation's Inkley.

Preservation of these lands takes money and influence. Fortunately, hunters bring their wallets along on expeditions.

Fish and Wildlife estimated hunting expenditures at $22.9 billion nationwide in 2006, a huge amount that gives many local economies a boost and incentive to keep their environments preserved.

"Hunting is something that gives a game species a value it didn't have before," said Hosmer. "And it creates commerce in communities around the United States, and around the world such as eastern and southern Africa."

This value is recognized by the suppliers of everything "hunting," from ammo and guns to lodging and trip outfitters. The species hunted becomes a valuable commodity and every effort is made to protect it and its habitat.

Plus, the federal government has imposed an excise tax of approximately 10 percent on hunting goods and services.

"Hunters, being the most ardent conservationists around, strongly support the federal excise tax because it raised 400 million dollars, which was then given to state conservation agencies to manage the wildlife and preserve the lands they hunt," noted Inkley.

Hunting is also a natural way of keeping certain species from overpopulation.

"Overpopulation has detrimental effects that ripple through the entire ecosystem," explains Inkley. "Overgrazing by the white-tailed deer changes the entire plant species and composition of the forest. For instance, deer can eat all the red maple, so species that rely on the red maple dwindle."

Another major problem with species overpopulation is that it increases interaction with humans, often in unfavorable ways. The Insurance Institute for Highway Safety estimates that there are more than 1.5 million deer-vehicle collisions each year, and about 150 of those end up being fatal to humans.

Animal lovers would argue that overpopulation is not the problem; our ever-expanding desire to live in the suburbs is at fault.

"All in all, we bulldoze the natural habitats of these species, and they have nowhere to go," says Nicole Matthews, spokesperson for People for the Ethical Treatment of Animals (PETA) "Plus, we've killed off the predator species for coming too close to our homes, and these predators are responsible for regulating populations naturally. Nature has a way of regulating itself."

It could be argued that there is a greener way to preserve the animals and their natural habitat, a method that's catching on with younger generations.

Ecotourism is on the rise. Hunting was only 4 percent of recreational-visitor days to wildlife refuges in 2006, as opposed to 80 percent for "non-consumptive activities," according to Fish and Wildlife.

"People should do environmentally friendly activities like kayaking, camping, bird-watching, and wildlife photography," says PETA's Matthews. "This truly respects all habitats and wildlife."

For those who rely on hunting instead of the supermarket for their meat, Matthews has an argument against that too — one that may be hard to swallow for millions of dedicated hunters who won't be easily persuaded to trade their rifles for a farmer's market.

"If you have a lust for meat, consider your health. Meat is full of cholesterol and saturated fat and devoid of fiber. A vegetarian diet isn't only more environmental it helps to prevent heart disease, cancer, and stroke," she says. "The best way to protect animals and their environment is to leave them off of your plate."

That's a conclusion that might be hard to swallow for the millions of dedicated hunters not easily persuaded to put down their guns and hit the farmers' markets.