A study of the seasonal booming activity of the Bittern Botaurus stellaris; what is the biological significance of the booms?

Abstract

Booming activity was studied in five focal male Bitterns Botaurus stellaris at two different marshlands of central Italy. For each individual, the length of the booming season, the seasonal and evening pattern of booming rate, the seasonal pattern of booming effort and some characteristics of the boom “trains” (sequences of calls) were studied. The lack of a common pattern of vocalization was noted, while the booming males showed individual patterns with regard to all the above characteristics. The length of the booming season and the booming effort differed at the two sites. While one bird was unique with respect to the quality of the vocalizations, a common characteristic of the remaining four focal birds was a marked increase or resurgence in booming activity in a period of the breeding season which coincided with the presence of the nestlings. Mainly on the basis of this particular seasonal vocalization pattern, we discuss the possible meaning of the booming activity of the male Bittern. One function of the booming activity suggested is the defence of a feeding territory, where the females of the booming male can find food to feed the nestlings. For the male, this appears to be his only contribution to the rearing of the offspring.