Translated from the blog of Staatsbosbeheer in the rivers country of Gelderland province in the Netherlands today, about ringing birds in Gelderse Poort nature reserve:
During the first ring session of 2016, on April 21, there was an unexpected and extraordinarily spectacular catch. A Moustached Warbler hung in the net. This south and south-east European species had never been observed in the Netherlands. The bird was photographed after the ringing and immediately released back into the area. In the evening the bird was found singing close to the ringing spot. Because the Moustached Warbler was heard from the public road and a lot of birders were already aware of the catch it was decided to release the location. On April 22 the singing bird was visited by about 300 birdwatchers and over 100 birdwatchers have heard the bird on April 23.
This Dutch regional TV video says that on 24 April 2016, the rare bird was gone. A moustached warbler had been seen for the first time ever in Belgium in 2015.