While morphological traits are often associated with multiple functions, it remains unclear how evolution balances the selective effects of different functions. One possibility is that axes of trait variation (e.g., shape and size) should correlate with different functions. Alternatively, constraint or mutually exclusive optima may produce traits that are a compromise between functions (i.e., a trade-off). To clarify how functional traits may influence divergence in signaling behavior, we also aimed to connect changes in morphology to their consequences for vocal performance. We quantified beak shape using geometric morphometrics and compared this trait to foraging behavior, climatic variables, and song characteristics in a phylogenetic comparative study of an Australasian radiation of songbirds (honeyeaters, Meliphagidae). We found that both climate and foraging behavior were significantly correlated beak shape and size. We also found that evolutionary changes in beak morphology have significant consequences for vocal performance: species with elongate-shaped beaks sang at higher frequencies, while species with large beaks sang at a slower pace. These results highlight how morphological traits can represent an evolutionary compromise among functions, and suggest that specialization along any such axis may increase ecological divergence or reproductive isolation along others.