Reproductive success, natal dispersal, and recruitment in a song sparrow (Melospiza melodia) population breeding in California coastal scrub

In this dissertation, I test several hypotheses concerning the determinants of reproductive success, natal dispersal and juvenile recruitment in individual Song Sparrows (Melospiza melodia). I studied Song Sparrows at two sites in California coastal scrub habitat that differed significantly in vegetative structure and species composition. I also analyzed long-term variation in population demographics using data that were collected as part of an ongoing monitoring program.; Reproductive success of individual Song Sparrows was related both to nest site characteristics and to annual weather variables. Nest predation was the major cause of reproductive failure. Nest predation was significantly related to several characteristics of the nest patch habitat and nest placement, but these relationships differed between the study sites. Song Sparrows placed their nests non-randomly with respect to nest patch characteristics, but preferred habitat characteristics were not necessarily associated with nest success.; Song Sparrow reproductive success was higher in years with higher rainfall, due to increases in the probability of nest survival and the length of the breeding season. Song Sparrows also nested over a longer time period in years with higher summer temperatures, and there was an increase in the number of successful broods per female in wetter, cooler years. I found no evidence for decreased reproductive success in years of higher population density, suggesting that reproductive success was limited primarily by density-independent factors. Rainfall-associated variation in reproductive success appeared to have a strong influence on population density.; Juvenile survival was unrelated to population density or weather, but young that were heavy relative to their nest-mates were more likely to survive and breed on the study area. Natal dispersal was related to both juvenile and adult population density, but the direction of the relationships differed. Dispersal distances were shorter in years when larger numbers of juveniles were present, but were longer when adult density was high in the year following hatching. Females that hatched where local population density was high dispersed shorter distances than those that hatched where local density was low. This dissertation illustrates the important influence of environmental variation on the behavior, individual fitness, and population dynamics of Song Sparrows.