Although there are nearly 500 American UAVs in Iraq, each of them averages only about 20-30 minutes use a day. This is mainly because over 80 percent of the UAVs are of the micro (under ten pounds) variety, and belong to battalions or brigades. When these units are not out on a major operation, their micro-UAVs are kept on the ground. No ones being greedy, its just that the micro-UAVs are neither bullet proof (the terrorists know how dangerous the UAVs are for them, and fire away whenever they spot one), nor indestructible (most are expected to wear out after a few dozen missions). So units with micro-UAVs, use them only when they have to. Replacements, and spare parts, are often hard to come by, and everyone now knows that the UAVs can be a lifesaver in combat. The larger UAVs, like the air force Predator and the army Hunter and Shadow, are in short supply. 

But theres another problem UAVs are encountering; congested air space. Each of the services has different rules, and procedures for dealing with air command and control systems. Most important, is the need to avoid collisions up there. Not just between aircraft (manned or unmanned), but especially between aircraft and projectiles (rockets, missiles, artillery and mortar shells). UAVs present a new problem, because the majority of them (the micro-UAVs) fly close to the ground (from 100-1000 feet) and tend to stay in one area for a long time. While the UAVs are at risk from mortar or artillery shells landing in the area, they are also a danger to helicopters flying in the vicinity. All of the services are seeking a better way to do this, and the most promising solution seems to lie in the new networking and information systems coming into use. But for the moment, keeping the UAVs as safe as possible up there is more art than science.