SPERM DEPLETION IN THE BENGALESE FINCH, LONCHURA-STRIATA

Sperm are limited in the Bengales finch; three copulations in 3 h result in a 95% reduction in sperm numbers transferred. Recovery from sperm depletion occurs within 24 h. Pairs in captivity copulate about 15 times per clutch and about twice each day in the 5 days before egg laying. Sixty-eight percent of behaviorally successful copulations result in sperm transfer, with some males performing consistently better than others. Single ejaculates contain 2.9 x 10(6) sperm, the testes (combined mass: 0.103 g) comprise 0.7% of male mass, and the seminal glomera hold sufficient sperm (7.7 x 10(6)) for two or three inseminations. The intervals between successive copulations were significantly more uniform than expected by chance, indicating that males allocate their ejaculates prudently. Conflicts of interest between males and females within monogamous pairs exist over the timing and frequency of copulation; the resolution of these conflicts is discussed.