A C206 pilot orbiting with a clearance in Class B airspace reported a NMAC with a B747 descending on a visual approach.

Narrative

Cessna 206 was performing operations approximately 2nm N of ZZZ1 at 3500 MSL At completion of assignment the C206 requested repositioning to orbit ZZZ at 4;000 MSL with a Bravo Clearance. Request was made to ATC on XXX.XX. ATC directed the C206 to proceed on course and remain at 3500 until clear of traffic departing ZZZ2. When clear of traffic; ATC approved climb to 4000. Arriving over ZZZ at 4000 the C206 commenced an orbit with left hand turns. ATC directed the C206 to contact ATC on XXX.XY. C206 checked in with ATC and reported orbiting ZZZ at 4000. ATC acknowledged. Shortly after contacting ATC (approximately 30 seconds) the C206 received an ADS-B traffic alert of converging traffic at the same altitude. The crew observed a B747 at approximately 1-1.5 mile distance at about 2 o'clock. C206 crew disengaged autopilot and commenced a climb. From ADS-B data it appeared the B747 was also commencing a descent. The C206 received a traffic alert from ATC that a B747 was at 3 o'clock and 3700 feet. The C206 and B747 crossed with near zero horizontal separation and an estimated vertical separation of 400-500 feet. The position and flight path of the B747 appeared to be a off-normal situation not normally observed by the C206 crew who routinely orbit ZZZ at 4000 during operations. Contributing events were 1) The unusual flight path of the B747. 2) A hand off of the C206 to another frequency without a traffic advisory. 3) A late hand off that did not leave the C206 crew time to gain situational awareness of traffic. 4) A late traffic advisory after radio hand off. 5) The C206 crew did not fully utilize ADS-B traffic data at a sufficient distance range to gain situational awareness. 6) The flight path of the B747 was similar to aircraft making visual approaches to RWY XX at ZZZ1 however the altitude was approximately 2000 feet higher than the typical approach. This similarity of the flight path to normal operations made it difficult to quickly identify and interpret the conflict visually at night.