The National Park Service is taking steps to ban drones from 84 million acres of public lands and waterways, saying the unmanned aircraft annoy visitors, harass wildlife and threaten safety.

Jonathan Jarvis, the park service's director, told The Associated Press he doesn't want drones flushing birds from their nests, hovering over rock climbers as they cling to the sides of cliffs or buzzing across the face of Mount Rushmore.

Jarvis said he would sign a policy memorandum on Friday directing superintendents of the service's 401 parks to write rules prohibiting the launching, landing or operation of unmanned aircraft in their parks.

Two large national parks, Grand Canyon in Arizona and Zion in Utah, have already changed their rules to ban drones. Some other parks have interpreted existing regulations to permit them to ban drone flights, but Jarvis said each park must change its "compendium" — a set of regulations unique to that park — if a ban is to be enforceable.

At Yosemite National Park in California, where officials announced last month they would adopt a policy prohibiting drone flights, hobbyists have been using unmanned aircraft to film the park's famous waterfalls and capture close-up shots of climbers on its granite cliffs. Zion officials were spurred to take action after an incident in which an unmanned aircraft was seen harassing bighorn sheep and causing youngsters to become separated from their herd.

At Mount Rushmore in South Dakota, park rangers last September confiscated an unmanned aircraft after it flew above 1,500 visitors seated in an amphitheater and then over the heads of the four presidents carved into the mountain.

"Imagine you're a big wall climber in Yosemite working on a four-day climb up El Capitan, and you're hanging off a bulb ready to make a (difficult) move, and an unmanned aircraft flies up beside you and is hovering a few feet from your head with its GoPro camera running," Jarvis said in an interview. "Think about what that does to your experience and your safety,"

Some drone operators have complained that a ban favors some park users over others. They also say many unmanned aircraft flights are made without incident and with respect for other park users and wildlife.

Unmanned aircraft range from no bigger than a hummingbird to the size of an airliner, and their capabilities are improving rapidly. Use is growing as their price tags decline. The park service wants to get out in front of that by putting in rules place now, Jarvis said.

"This is a different kind of aircraft, and it is being used in different ways than what we have seen from the (model aircraft) hobbyists," he said. "We want to have some control over it now before it proliferates."

The memorandum directs superintendents to continue to allow model aircraft hobbyists and clubs that already have approval to operate in some parks to continue to do so. Also, parks can continue to grant permits for drone flights for other purposes like research, search and rescue, and firefighting, he said. Commercial operators like moviemakers can also apply for a permit to operate a drone, he said.

"We would have to hear why they would necessarily need this type of equipment in order to accomplish their goals," Jarvis said.

While parks are changing their individual rules, the park service will be drafting its own rule to ban drone flights in parks nationwide, he said. Jarvis said he hopes to have a proposal ready in about 18 months.

The ban only affects what Jarvis described as "operations inside parks," and not high altitude flights over parks.

The park service has been working closely with the Federal Aviation Administration, although the service's action is separate from the FAA's ban on commercial drone flights, he said.

The FAA ban is being challenged by commercial drone operators.

Two years ago, Congress directed the FAA to put regulations in place provide for the safe integration of commercial drones into the national airspace. The regulations were supposed be finished by September 2015, but the agency isn't expected to make that deadline.