While the lark buntings are socially monogamous, there is extensive extra-pair mating, observed through extra-pair paternity. In songbirds, it is suggested that social monogamy exists because of limited opportunities for polygyny. As expected, there is considerable aggression between males and between females, competing for mates. Many males are unable to find a social mate, which can be attributed to male-biased breeding sex ratio, social monogamy, and the frequency of extra-pair paternity. Acquisition of a social mate is an essential element of a male's fitness, thus social mating success plays a significant role in variable selection of male traits.