SEASONAL DECLINE IN REPRODUCTIVE-PERFORMANCE OF SONG SPARROWS

Clutch size in Melospiza melodia declined in the population through the breeding season due to some classes of females both nesting later and laying smaller clutches. Later laying and smaller clutches of yearling females were a major contributor to seasonal decline in clutch size, although seasonal decline in clutch size was also observed within age classes of females. Hatching success was c10% lower for 2nd broods than 1st broods, but did not vary with date that the nest was initiated. Survival of offspring did not vary seasonally during the period that offspring were in the care of their parents. Although nestling size was greater later in the breeding season, the probability of independent offspring recruiting into the breeding population was lower for young born later in the breeding season. The seasonal decline in recruitment of offspring was not due to differences in the quality of territories or parents. -from Author