Brought back 7 hives from a pumpkin field last sun. All were light on stores. Sooo, I decided to set up an open feeder (A plastic pail with a 1-1 sugar syrup mixed with an equal amount of hfc). Yesterday I noticed about a half cup of bees in a pile on the wooden grid in the pail. This evening there is probably 4 times that number. In the morning I plan on removing the feeder befor the bees are up & about. Does anyone have any idea what is going on? Pictures attached.