A STUDY OF THE SEASONAL BOOMING ACTIVITY OF THE BITTERN BOTAURUS-STELLARIS - WHAT IS THE BIOLOGICAL SIGNIFICANCE OF THE BOOMS

Booming activity was studied in five focal male Bitterns Botaurus stel laris at two different marshlands of central Italy. For each individua l, the length of the booming season, the seasonal and evening pattern of booming rate, the seasonal pattern of booming effort and some chara cteristics of the boom ''trains'' (sequences of calls) were studied, T he lack of a common pattern of vocalization was noted, while the boomi ng males showed individual patterns with regard to all the above chara cteristics, The length of the booming season and the booming effort di ffered at the two sites, While one bird was unique with respect to the quality of the vocalizations, a common characteristic of the remainin g four focal birds was a marked increase or resurgence in booming acti vity in a period of the breeding season which coincided with the prese nce of the nestlings. Mainly on the basis of this particular seasonal vocalization pattern, we discuss the possible meaning of the booming a ctivity of the male Bittern. One function of the booming activity sugg ested 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 a ppears to be his only contribution to the rearing of the offspring.