Hummingbirds are one of only a small number of animal groups to have developed the trait of vocal learning. By studying the brain structures hummingbirds use in vocal learning we can learn about the requirements on the brains of all vocal learning species.
The rufous-breasted hermit (top) produces songs with complex syntax, whereas the sombre hummingbird (middle) produces complex syllables, but simple stereotyped syntax, and the white-throated hummingbird (bottom) produces simple syllables and syntax.
Hummingbirds have developed a wealth of intriguing features, such as backwards flight, ultraviolet vision, extremely high metabolic rates, nocturnal hibernation, high brain-to-body size ratio, and a remarkable species-specific diversity of vocalizations. Like humans, they have also developed the rare trait of vocal learning, i.e. the ability to acquire vocalizations through imitation rather than instinct.
Using behaviorally-driven gene expression in freely-ranging tropical animals, we show that the forebrain of hummingbirds contains 7 discrete structures that are active during singing, providing the first anatomical and functional demonstration of vocal nuclei in hummingbirds. These structures are strikingly similar to 7 forebrain regions involved in vocal learning and production in songbirds and parrots the only other two avian orders known to be vocal learners. This similarity is quite surprising, as songbirds, parrots, and hummingbirds are thought to have evolved vocal learning and associated brain structures independently suggesting that strong constraints influence the evolution of forebrain vocal nuclei.
Click here for PDF file of a Nature article describing the presence of vocal brain structures in hummingbirds and the relevance for the evolution of vocal learning. (You need to have Adobe Acrobat.)