Birds are remarkably diverse, both in terms of species richness and diversity in phenotypes. A longstanding goal in evolution and ecology is to document patterns of biodiversity and infer the biological processes that contribute to speciation and phenotypic evolution. Here, I take a multidimensional approach to examine the tempo, mode, and mechanisms of phenotypic evolution and speciation in birds. I first document a positive association between rates of vocal evolution and speciation in two large lineages in Neotropical birds. I then explore phenotypic and genetic variation in two lineages of songbirds: the White-collared Seedeater (Sporophila torqueola) and the Holarctic redpoll finches (Acanthis sp.). Finally, I quantify phenotypic change in Horned Lark of the Imperial Valley in southern California, where the desert has been transformed into agricultural land. Collectively, these studies provide different perspectives on avian biodiversity and together illustrate the immense value of natural history collections as repositories of phenotypic and genetic data.