The Rossitten Bird Observatory (Vogelwarte Rossitten in German) was the world's first ornithological observatory. It was sited at Rossitten, East Prussia (now Rybachy, Kaliningrad Oblast, Russia), on the Curonian Spit on the south-eastern coast of the Baltic Sea. It was established by German ornithologist Johannes Thienemann and operated until 1944. In 1945 East Prussia was divided between Poland, Russia and Lithuania, and most ethnic Germans expelled.