A band of large drones appears to be flying nighttime search patterns over northeast Colorado — and local authorities say they don’t know who’s behind the mysterious aircraft.

The drones, estimated to have six-foot wingspans, have been flying over Phillips and Yuma counties every night for about the last week, Phillips County Sheriff Thomas Elliott said Monday.

The drones stay about 200 feet to 300 feet in the air and fly steadily in squares of about 25 miles, he said. There are at least 17 drones; they emerge each night around 7 p.m. and disappear around 10 p.m., he said.

“They’ve been doing a grid search, a grid pattern,” he said. “They fly one square and then they fly another square.”

The sheriff’s office can’t explain where the drones are coming from or who is flying them. The estimated size and number of drones makes it unlikely that they’re being flown by hobbyists, Undersheriff William Myers said.

The Federal Aviation Administration told the sheriff’s office that it had no information on the drones, and the U.S. Air Force said the aircraft aren’t theirs, Elliott said.

A spokesman for the Drug Enforcement Administration told The Denver Post on Monday that the drones aren’t operated by the agency. A spokesman for the FAA said that agency likely has no information on them. Drone pilots aren’t required to file flight plans, unless they’re flying in controlled airspace, like near an airport.

Officials with the Air Force and the Department of Defense did not immediately return The Post’s requests for comment on the mystery aircraft Monday. U.S. Army Forces Command spokesman John Boyce said Monday he was not aware of any training involving military drones in that area.

“Do not seem to be malicious”

On Friday, Myers said he watched eight of the large drones flying along the Yuma County border near the intersection of U.S. 385 and County Road 54. At the same time, a single drone hovered about 25 miles away over the town of Paoli — it didn’t move all night, just hovered over the town — and eight more drones flew over Haxtun, about 10 miles down the road from Paoli, Myers said.

“Overhead they were probably doing 30, 40 mph,” he said. “They weren’t racing or flying around with speed.”

One resident who spotted a drone last week gave chase, Elliott said, driving behind it at about 50 mph, but lost the drone when he ran out of gas in Washington County.

The machines fly too high to be heard from the ground but can be seen by their strobing white lights along with red, blue and green lights, Myers said.

Myers suspects the drones might be operated by a private company, although the machines haven’t targeted any obvious landmarks or features — sometimes they fly over towns, other times over empty fields.

“They do not seem to be malicious,” Elliott said. “They don’t seem to be doing anything that would indicate criminal activity.”

Vic Moss, a Denver-based commercial photographer, drone pilot and co-owner of an online drone school called Drone U, said Monday he’d bet either a company or a government agency is flying the aircraft.

“We have a number of drone companies here in Colorado, and they’re very innovative,” he said. “So maybe they’re testing something of theirs out in that area because it is very rural. But everyone that I know of, they coordinate all that stuff with local authorities to prevent this very situation. They all very much want people to understand drones and not cause this kind of hysteria.”

The grid pattern suggests the drone operators might be creating a map or carrying out a search, Moss said, although he added that some drone operators will fly at night in order to use infrared cameras, which are sometimes used in agriculture to examine crops.

He urged people not to try to shoot the drones down, both because their batteries can cause intense fires and also because shooting a drone is a federal crime.

“It becomes a self-generating fire that burns until it burns itself out,” he said. “If you shoot a drone down over your house and it lands on your house, you might not have a house in 45 minutes.”

Even if the sheriff’s office identified the pilot or pilots of the drones, they’re likely not breaking any laws, Myers said.

“The way Colorado law is written, none of the statutes fit for harassment or trespassing,” Myers said. “Colorado hasn’t gotten on board with identifying the airspace around your property as the actual premises, so we don’t have anything we could charge.”

“We know they exist”

The FAA does have rules for drones that weigh less than 55 pounds and requires such aircraft to be flown during daylight hours, within sight of the pilot, no higher than 400 feet above the ground, and not over people, among other rules. However, pilots can apply for and receive waivers from the FAA that exempts the pilots from many of those rules.

It’s also not clear whether the drones over Phillips and Yuma counties would be governed by those regulations. A drone the size of the ones spotted over the counties likely would weigh more than 55 pounds, Moss said. That means the drone operator would be flying commercially and would likely need to be a “manned aviator” — an actual pilot, Moss said.

Chuck Adams, CEO of 1Up Aerial Drone Services in Golden, said that he wasn’t sure who might be flying the drones, but said his company does offer “drone defense” systems that can help people on the ground discover where drones are being flown from.

“It’s something we put up with radio frequency and acoustics, and you can tell where the operator is and where the drones are,” he said. “We can’t take them out of the sky, but we can give awareness.”

Elliott said Monday that the sheriff’s office has received nine calls about the drones since last week. He said residents no longer need to call to report a simple sighting of the drones.

“We just want to know if one lands, if we can get our hands on it, or if they see someone operating them, that’s what we’re looking for now,” he said. “We know they exist.”

He added that there is one culprit he can certainly rule out as the drone operator, even though it’s the week before Christmas.

“It’s not Santa or his reindeer,” he said.