The results also suggest that the final outcome of sperm competition may be partly dependent on the female bird. (sciencedaily.com)
An alternative theory suggests they're not stuck at all: it's plain old selfish behavior explained by sperm competition. (discovermagazine.com)
By checking how many offspring carried the mutant eye - color, they discovered that some males were better at sperm competition than others. (sciencemag.org)