PROLONGED COPULATION, SPERM RESERVES AND SPERM COMPETITION IN THE AQUATIC WARBLER ACROCEPHALUS-PALUDICOLA

The Aquatic Warbler Acrocephalus paludicola has a quasi-promiscuous ma ting system with high levels of multiple paternity and, thus, intense sperm competition. The duration of copulation in the Aquatic Warbler i s unusually long. In hand-reared, captive birds the duration of mounti ng was 23.7 +/- 11.8 min (mean +/- s.d.). On average, six cloacal cont acts (inseminations) occurred during each copulation. Between insemina tions the male remained in contact with the female, either on top of o r directly behind her. Protracted copulation may be a form of contact mate guarding, a behaviour not previously recorded in birds, Copulatio n was most frequent during the evening and early morning. Male Aquatic Warblers also exhibit extreme morphological adaptations of their repr oductive system compared with other Acrocephalus species and other bir ds: their testes, cloacal protuberance and seminal glomera (which cont ain 198 x 10(6) spermatozoa) are all relatively large. Frequent insemi nation during protracted copulation and contact mate guarding may be a lternatives to paternity guarding found in other birds.