Repeatable Reproduction in Song Sparrows

Abstract

I looked for evidence of consistent variation in individual quality of breeding females in a population of Song Sparrows (Melospiza melodia). Consistent differences in individual quality were detected by looking for correlations in reproductive parameters between nesting attempts. Seven reproductive traits were examined for evidence of variation in individual quality. In addition, I determined whether the degree of repeatability was affected by differences in conditions among years, by female age, or by success of previous nesting attempts. There were consistent differences among females in the date of initiation of nesting, clutch size, egg mass, and nutritional condition of offspring. The differences in egg mass between females may be heritable. There was evidence that repeatability of nestling condition is influenced by the success of previous nesting attempts. Although consistent differences were found in quality of female sparrows, there were no ''superparents.'' Females that were good at one given aspect of reproduction were not proficient at all facets of reproduction.