It's funny you mentioned that, because I just noticed the same exact thing in some of my colonies I just inspected. I had drones all over the place a few weeks ago, and now I see very few, if any. I think it's probably due to the flow stopping so suddenly a few weeks ago. Most of the drone cells now are either empty or being used for nectar storage. Got to keep an eye on the stores, some are getting light very quickly. I'm sure they sense lean times and the drones are the first to go.