Since its passage, the Act has been credited with helping to bring dozens of animal and plant species back from the brink of extinction.
Perhaps the most well-known success has been the recovery of the Gray Wolf in the American West, a region in which the animals had been effectively exterminated over the past century. Since wolves were reintroduced to Yellowstone National Park a decade ago, their numbers have increased dramatically.
Tens of thousands of avid wolf watchers travel to the park each year to see the predators, which can be spotted easily from the side of the road.
But the wolf recovery program has also had its critics.
Rancher Martin Davis drives his pickup truck slowly up a rugged mountain road that leads to the high valley where his cows graze each summer among willow and aspen trees. It is a remote and peaceful spot about an hour away from his ranch.
His wife attaches an antenna to a radio receiver tuned to pick up a very important signal - the trademark chirps of radio-collared wolves.
"We are trying to see if there is a wolf signal," he explains. "There are two collared wolves in the area and I have gone to their frequencies and have not got a signal. If there were a signal there would be kind of a chirp sound on here and apparently one of the collared ones isn't close."
But he worries that his cows are never safe from wolf attacks. Fellow Rancher Bruce Malcolm, along for the ride, agrees. Their land borders Yellowstone and both have been outspoken critics of the move to reintroduce wolves to the area.
Wolves and cattle do not mix. I knew that there would be definite problems.
We've lost cows, and it is extra effort to guard your animals when wolves are around. But lots of times we get up in the middle of the night to check our cows because we hear a wolf howl. And so we have lost a lot of sleep patrolling in the middle of the night.
And, that's exactly right. You used to check the cows maybe once a week in the summertime when things get busy. Now we have to check them at least every other day, if not every day and so your time is spent in doing the cow checking that you wish you could be doing something else.
Yet you have been made to accommodate. It is a felony to kill a wolf.
Oh, absolutely. There is no way for you to protect yourself. There is nothing you can do with the wolves. We have just had to absorb all the loss. And, one of the biggest things that we suffer is the stress on our lives.
The human presence seems to help to push the wolves away and so if you are out there at least you are hopeful that the wolves will leave the cows alone while you are there.
So this [human presence] is your only recourse.
Yes, it is about all we have got.
Bruce Malcolm and Martin Davis walk among the cows in the upper valley pasture. The ranchers say they want to protect a way of life that their families have enjoyed for generations.
This is home for us. It gives us a sense of peace, a sense of belonging and a great sense of responsibility because we are just here for a little while and it is ours to take care of, and we need to take care of it. It is in our blood to take care of the land and the livestock that goes along with it, including wild livestock.
You see yourself as a steward of the land, a conservationist.
That is what we try to be, a steward of the land. That is our way of life.
And the wolf presents a problem.
It presents a problem, upsets the balance.
There is a certain amount of folks that say we have to get rid of wolves. We don't want them here. [But] that is past. They are here. We have to figure out a way to survive with them. I don't know the answer to that right now, but we have to get on with life. We have got to figure out some way to get along.
And, it is the job of the U.S. Fish and Wildlife Service to make that happen. The agency is charged with managing wolf recovery and it works with ranchers to try to minimize conflicts with the predator.
Nuisance wolves are harassed by noisemakers and shocked by electric fences. Problem animals are relocated or, as a last resort, killed.
On this day, field biologist Val Asher offers a crew at the Sun Ranch rubber-bullet training, an effective means to scare away predators. Ranch manager Todd Graham takes a shotgun, loads the ammunition, swings the gun barrel up, takes aim and fires at a wooden target.
"You want me to do this from here? Are you watching?" Val Asher asks.
So the object is to harass the wolves so they run away
"Exactly!" replies Asher.