New results from a 20-year study of free-living song sparrows confirm that attractive males contribute more offspring than less attractive males. They also reveal that the offspring of preferred males produce more descendents themselves. Females prefer males with a large song repertoire, which further work shows is a condition-dependent indicator of male quality.
Cotton, S., Rogers, D. W., & Pomiankowski, A. (2005, May 10). Sexual selection: The importance of long-term fitness measures. Current Biology. https://doi.org/10.1016/j.cub.2005.04.023