Why do male European sedge warblers with elaborate songs gain mates early in spring?

Male European sedge warblers (Acrocephalus schoenobaenus) with the most elaborate birdsongs gain mates early in the spring because female sedge warblers exhibit a strong preference for these complex vocalizations.1

This phenomenon is consistent with the runaway selection hypothesis, which suggests that certain courtship traits evolve rapidly because females preferentially mate with males possessing the most extreme or elaborate versions of those traits. In the case of the sedge warbler, the song serves as a key indicator of quality, leading females to select males with the longest and most intricate song repertoires, thereby allowing those males to secure mates earlier in the breeding season.1