If singers are successful at finding or attracting a female at higher swimming speeds, then why do nearly one-third of males only swim slower while singing? Are these younger or less physically fit males, or is this one of several strategies that males adopt depending on a context that we cannot yet observe? Given that swimming fast is energetically costly and possibly an indication of a male's physical stamina, this suggests that our results showing a highly significant inverse relationship between swimming speed and amount of singing is consistent with the conclusion, although highly speculative, that swimming speed can be an honest signal by which conspecifics assess male quality. 5.
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