The male indigo bunting is more brighly colored than the female.

Although socially monogamous (males and females form pair bonds during the breeding season), these birds exhibit genetic promiscuity by mating outside the pair.

An average of 13% of all matings involve extrapair copulations (EPCs).

DNA analysis by electrophoresis also reveals 27.2% to 32.1% of indigo bunting offspring are produced by EPCs.