The Caspian Gull (Larus cachinnans) has recently spread from Ukraine (northern coast of the Black Sea, River Dnipro) to Poland, Czech Republic, Germany and into The Netherlands. The first breeding bird in The Netherlands was documented as recently as in 2012, when a 5^th calendar year male partner formed a mixed pair with a female Herring Gull, at Nederrijn near Amerongen. The couple raised a single, hybrid chick from a clutch of three eggs (Gelderblom 2012). In 2014, a more or less resident adult pair of Caspian Gulls was seen at De Kreupel (IJsselmeer), and in the next four years more and more breeding attempts were documented at De Kreupel and on breakwaters near Lelystad. In 2019, at least 12 pure pairs of Caspian Gulls and a mixed pair bred near Lelystad, while four pairs were found at De Kreupel (Kelder et al. 2023). In 2020, the population had apparently exploded, when 42 breeding pairs were detected on these two locations only (15 at De Kreupel, 27 near Lelystad). Some of the breeding birds were ringed as chicks in Poland (Babice en Paczków) and in the eastern half of Duitsland (Gräbendorfer lake).