Your engine is "sumping" which means oil from the tank is draining into the crankcase. When started the pressure from the pistons moving down causes pressure and the oil has to leave. By the crankcase vent. The cause is the oil pump check valve is not seating perfectly, and a tiny amount seeps past daily. There are several temporary fixes, too many for me to list now. Google "harley oil sumping" to see if you want to do a temp. or permanent fix. A quick check is to pull the oil pump check ball and see if it has debris or wear marks. This is located under that BIG strange looking straight screw head on top of the oil pump (on the engine case,behind the cam cover) the ball can be removed with a pencil magnet.
P.S. I'm not a Harley guru, just a guy with oil-stained garage concrete.