Abstract
In recent years, the breeding populations of many migratory songbird species have declined in the Carpathian Basin. However, there may be significant differences between different geographical regions, as most species have a much higher chance of successful breeding in protected areas. This is also the case for the Moustached Warbler, one of the most habitat-specialist passerine. It colonises only perennial, unharvested reedbeds, therefore its conservation management is essential. We studied the population changes of this species between 2001 and 2022 at Lake Kolon in Izsák, based on bird ringing data from 10–24 July. Data of 12,817 ringed and 5,075 recaptured birds were used in the analyses. The annual capture rate decreased significantly during the study period. The proportion of juveniles was higher at higher water levels during the whole breeding season. In contrast, when looking at winter and first and second broods separately, water level had no effect on the juvenile/adult ratio. This is because the birds compensate for unsuccessful first broods by increasing the proportion of second and replacement broods. If the first broods are successful, the ratio of second and replacement broods will be lower. As reed management is practically non-existent in this area, the perennial reedbeds provide suitable nesting conditions for the species. Changes in the wintering sites may be responsible for the declining trend. Protection of the area is of particular importance for the conservation of the species.