In the breeding season of 2004 in sewage sedimentation basins overgrown with semi-natural reedbeds (n = 63, total area = 113.3 ha, mean area = 1.80 (± 3.90) ha, range: 0.018 do 26.54 ha) on a sewage farm (total study area 14.22 km²) in the northern part of Wrocław city (640 000 inhabitants, SW Poland) 45 territories of Bluethroat Luscinia svecica cyanecula were found. Territorial birds were detected in 38% of all controlled reedbeds. Up to eight territories were localized in a single reedbed. In at least ten territories (22% of all) the presence of breeding pairs was also recorded. The smallest reedbed occupied by a single male had 0.081 ha and by a pair – 0.204 ha. A high statistically significant correlation was found between the reedbed area, the length of its border and the number of territories it contained. The probability of Bluethroat occurrence in a reedbed was closely related to its size. Even in small reedbeds (<2 ha) it amounted to ca. 35% and it reached 100% at 10 ha. Within particular occupied reedbeds (n = 24) the densities ranged from 1.5 to 49.5 (exceptionally 123.4) territories 10 ha⁻¹. The average density (± SD) for all reedbeds (n = 63) was 7.6 (± 19.2) territories 10 ha⁻¹, while within the occupied reedbeds (n = 24) it amounted to 20.0 (± 27.1) territories 10 ha⁻¹. The Wrocław population of Bluethroat is one of the biggest known breeding concentration of this species not only in western Poland, but probably also in large part of central Europe. So far reports of marked increases of Bluethroat abundance in anthropogenic habitats (after a dramatic decline observed since the end of XIX century) have come mainly from western Europe.
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