Extraordinary occurrence of Pallas’s leaf warbler (Phylloscopus proregulus Pallas, 1811) in Bulgaria and the Balkan Peninsula in the autumn and winter of 2022/2023

Four Pallas’s leaf warblers (Phylloscopus proregulus) were captured at Durankulak ringing camp, NE Bulgaria, in frames of four days between 12 and 16 October 2022. The species is a rare vagrant in Bulgaria and neighbouring Balkan countries. It has not been captured and ringed neither at Durankulak nor elsewhere in Bulgaria until now. Annual population fluctuations and weather conditions are discussed as possible explanations for that influx.