Seasonal Tradeoffs in Reproductive Investment in a Multi-Brooded Passerine

Abstract

Abstract. Because investment in eggs is costly for birds, a female's body condition is expected to influence that investment. Moreover, resource availability can fluctuate by year, and older and younger females may acquire or allocate resources differently. Additionally, in multi-brooded species, females may make tradeoffs in investment in first and second clutches. Because environmental conditions often change through the breeding season and early maturity of second broods can increase females' fitness, patterns of females' allocation to each clutch may change with the season. Here, we investigate associations between females' quality (body condition and age) and pre-hatching investment (clutch size, average egg mass per clutch, and total clutch mass) in adults of the Eastern Bluebird (Sialia sialis), a multi-brooded cavity-nesting passerine. In the two years of the study, relationships differed; in 2003, females that were heavier relative to their body size produced larger eggs and invested in greater o...