The fear of the remote-controlled killing machines kept al-Qaeda militants looking at the sky most of the daylight, the letter said.
"The brothers who can keep a low profile and take the necessary precautions should stay, but move to new houses on a cloudy day" when visibility for US drones is reduced, bin Laden wrote.
He also encouraged al-Qaeda's leaders to stay far from their troops to reduce the likelihood of being killed.
According to Long War Journal which keeps tabs on the CIA-operated drone strikes, so far nearly 296 attacks have been carried out leading to killing of approximately between 1,492 to 2,300 militants since 2003.
