TIMBUKTU, Mali: One of the last things the bearded fighters did before leaving this city was to drive to the market where traders lay their carpets out in the sand.

The Al-Qaeda extremists bypassed the brightly colored, high-end synthetic floor coverings and stopped their pickup truck in front of a man selling more modest mats woven from desert grass, priced at $1.40 apiece. There they bought two bales of 25 mats each, and asked him to bundle them on top of the car, along with a stack of sticks.

“It’s the first time someone has bought such a large amount,” said the mat seller, Leitny Cisse al-Djoumat. “They didn’t explain why they wanted so many.”

Military officials can tell why: The fighters are stretching the mats across the tops of their cars on poles to form natural carports, so that drones cannot detect them from the air.

The instruction to camouflage cars is one of 22 tips on how to avoid drones, listed on a document left behind by the Islamic extremists as they fled northern Mali from a French military intervention last month. A Xeroxed copy of the document, which was first published on a jihadist forum two years ago, was found by the Associated Press in a manila envelope on the floor of a building here occupied by Al-Qaeda of the Islamic Maghreb.

The tip sheet reflects how Al-Qaeda’s chapter in North Africa anticipated a military intervention that would make use of drones, as the battleground in the war on terror worldwide is shifting from boots on the ground to unmanned planes in the air. The presence of the document in Mali, first authored by a Yemeni, also shows the coordination between Al-Qaeda chapters, which security experts have called a source of increasing concern.

“This new document ... shows we are no longer dealing with an isolated local problem, but with an enemy which is reaching across continents to share advice,” said Bruce Riedel, a 30-year veteran of the CIA, now the director of the Intelligence Project at the Brookings Institution.

The tips in the document range from the broad (No. 7, hide from being directly or indirectly spotted, especially at night) to the specific (No. 18, formation of fake gatherings, for example by using dolls and statues placed outside false ditches to mislead the enemy.) The use of the mats appears to be a West African twist on No. 3, which advises camouflaging the tops of cars and the roofs of buildings, possibly by spreading reflective glass.

While some of the tips are outdated or far-fetched, taken together, they suggest the Islamists in Mali are responding to the threat of drones with sound, common-sense advice that may help them to melt into the desert in between attacks, leaving barely a trace.

“These are not dumb techniques. It shows that they are acting pretty astutely,” said Col. Cedric Leighton, a 26-year veteran of the United States Air Force, who helped set up the Predator drone program, which later tracked Osama bin Laden in Afghanistan. “What it does is, it buys them a little bit more time – and in this conflict, time is key. And they will use it to move away from an area, from a bombing raid, and do it very quickly.”

The success of some of the tips will depend on the circumstances and the model of drones used, Leighton said. For example, from the air, where perceptions of depth become obfuscated, an imagery sensor would interpret a mat stretched over the top of a car as one lying on the ground, concealing the vehicle.

New models of drones, such as the Harfung used by the French or the MQ-9 “Reaper,” sometimes have infrared sensors that can pick up the heat signature of a car whose engine has just been shut off. However, even an infrared sensor would have trouble detecting a car left under a mat tent overnight, so that its temperature is the same as on the surrounding ground, Leighton said.

Unarmed drones are already being used by the French in Mali to collect intelligence on Al-Qaeda groups, and U.S. officials have said plans are under way to establish a new drone base in northwestern Africa.

The author of the tip sheet found in Timbuktu is Abdallah bin Mohammad, the nom de guerre for a senior commander of Al-Qaeda in the Arabian Peninsula, the Yemen-based branch of the terror network. The document was first published in Arabic on an extremist website on June 2, 2011, a month after bin Laden’s death, according to Mathieu Guidere, a professor at the University of Toulouse.

The tip sheet is still little known, if at all, in English, though it has been republished at least three times in Arabic on other jihadist forums after drone strikes took out U.S.-born cleric Anwar al-Awlaki in Yemen in September 2011 and Al-Qaeda second-in-command Abu Yahya al-Libi in Pakistan in June 2012. It was most recently issued two weeks ago on another extremist website after plans for the possible U.S. drone base in Niger began surfacing, Guidere said.

The idea of hiding under trees to avoid drones, which is tip No. 10, appears to be coming from the highest levels of the terror network. In a letter written by bin Laden and first published by the U.S. Center for Combating Terrorism, the terror mastermind instructs his followers to deliver a message to Abdelmalek Droukdel, the head of Al-Qaeda in the Islamic Maghreb, whose fighters have been active in Mali for at least a decade.

“I want the brothers in the Islamic Maghreb to know that planting trees helps the mujahedeen and gives them cover,” bin Laden writes in the missive. “Trees will give the mujahedeen the freedom to move around especially if the enemy sends spying aircraft to the area.”

Hiding under trees is exactly what the Al-Qaeda fighters did in Mali, according to residents in Diabaly, the last town they took before the French stemmed their advance last month.

In Timbuktu also, fighters hid their cars under trees, and disembarked from them in a hurry when they were being chased, in accordance with tip No. 13.

Along with the grass mats, Al-Qaeda men in Mali made creative use of another natural resource to hide their cars: mud.

Asse Ag Imahalit, a gardener at a building in Timbuktu, said he was at first puzzled to see that the fighters sleeping inside the compound sent for large bags of sugar every day. Then, he said, he observed them mixing the sugar with dirt, adding water and using the sticky mixture to “paint” their cars. Residents said the cars of Al-Qaeda fighters are permanently covered in mud.

The drone tip sheet, discovered in the regional tax department occupied by Abou Zeid, shows how familiar Al-Qaeda has become with drone attacks, which have allowed the U.S. to take out senior leaders in the terrorist group without a messy ground battle.