TIMBUKTU, Mali - One of the last things the bearded fighters did before leaving this city was to drive to the market.
The al-Qaida extremists stopped their pickup truck in front of a man selling mats woven from desert grass, priced at $1.40 apiece and bought two bales of 25 mats each.
"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 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.
The presence of the document, first authored by a Yemeni, in Mali also shows coordination among al-Qaida chapters.
"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 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.
"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 depth perception is difficult, an imagery sensor would interpret a mat stretched over the top of a car as one lying on the ground. New models of drones sometimes have infrared sensors that can pick up the heat signature of a car whose engine has just been shut off.
Unarmed drones are already being used by the French in Mali to collect intelligence on al-Qaida groups, and U.S. officials have said plans are underway to establish a new drone base in northwestern Africa.