Multiple maternity and paternity in single broods of apparently monogamous eastern bluebirds (Sialia sialis)

Abstract

In an effort to assess genealogical relationships between breeding adults and their putative offspring, we collected and analyzed blood from 257 wild, uniquely color-banded eastern bluebirds (Sialia sialis). Electrophoretic analysis of the protein products of two loci, esterase-2 (EST-2) and nucleoside phosphorylase (NSP), revealed that at least 5% of adult males and 15% of adult females were caring for at least one offspring not their own. Multiple parentage was evident in 9% of all broods sampled. Twenty-five percent of complete families sampled evidenced multiple parentage. Biparental care of nestlings by adult eastern bluebirds is not necessarily a reflection of the genetic kinship between putative parents and their offspring. The consort pattern among eastern bluebirds does not completely correlate with the pattern of gametic contributions, leading to a reconsideration of their mating system as possibly polygamous. This is among the first unambiguous observations of multiple patenity in a wild bird population, and of multiple maternity in a wild passerine. © 1984 Springer-Verlag.