Booming activity of male Bitterns Botaurus stellaris in relation to reproductive cycle and harem size

The relationship between vocalization rate and nesting parameters in the polygynous Great Bittern Botaurus stellaris was studied in a breeding population of eastern Poland. There was a difference between individuals in mean length of boom train and males with high booming rate had longer boom trains. No correlation between the booming parameters and components of breeding success and harem size has been found. However. females settled earlier in the territories of males with early start of booming activity and high vocalization rates. The peak of the calling activity season was synchronised with the female fertility period. These results suggest that in relation to the laying date the seasonal pattern of booming indicates a mainly intersexual function of vocal activity among bitterns.