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-Qaida 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-Qaida of the Islamic Maghreb.
The tipsheet reflects how al-Qaida'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-Qaida 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).
While some of the tips are outdated or far-fetched, taken together, they suggest the Islamists in Mali are responding to the threat of drones with sound, common-sense advice that may help them to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.
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.