Male sperm reserves and copulation behavior in the house sparrow, passer domesticus

The aim of this study was to measure the rates of sperm utilization and production in male house sparrows, Passer domesticus: this is the first attempt to do this for any wild bird. The number of spermatozoa in the seminal glomera of males on days -1 to +3 (i.e. during their partner's fertile period) declined significantly throughout the course of the day. Males had about 12.13 x 10(6) spermatozoa in their seminal glomera at the start of the day and during 16 copulations each day used 10.31 x 10(6) spermatozoa, which is probably all that was available for ejaculation. Mean ejaculate size was estimated to be 0.64x 10(6) spermatozoa. Seminal glomera occur only in passerines and their function is unclear, but our results suggest a new hypothesis: if spermatozoa production and spermatozoa transport to the seminal glomera are limited to a short period during the night, the seminal glomera serve as a daily spermatozoa store