This 1st CY Back-headed Gull was ringed on June 6, 2011 as pullus near Pryzkona Reservoir, Radyczyny, Turek, Poland (52.00 N 18.39 E), which is ~1000 km west of the Katwijk aan Zee observation spot. It was previously reported from the Starrevaart, Leidschendam on August 15, 2011, three weeks before the September 10, 2011 observation in Katwijk aan Zee.