A male, swallow-tailed hummingbird (Eupetomena macroura) perches on a branch at the nature reserve of the Museu de Biologia Mello Leitao, Espírito Santo, Brazil. Males, which are larger than females, are a colorful deep blue and green with a double tail like that of a swallow. Their song is quite variable and sung at a very low volume.
National Science Foundation (NSF)-supported researcher Erich Jarvis of Duke University is studying hummingbirds and their vocal structures. In 2002, Jarvis was awarded the Alan T. Waterman Award, NSF's highest honor for researchers under the age of 35. [See related images, Rufous-breasted hermit hummingbird and White throated hummingbird.]
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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, the ability to acquire vocalizations through imitation rather than instinct. Vocal learning is known to be present in only six groups of animals--three groups of birds (parrots, songbirds and hummingbirds) and three groups of mammals (bats, cetaceans [whales/dolphins] and humans). All other groups of animals are thought to produce genetically innate vocalizations. To understand this concept, it is important to distinguish vocal learning from auditory learning. Auditory learning is the ability to make sound associations, such as when a dog learns how to respond to the sound "sit." All vertebrates have auditory learning. Vocal learning is the ability to imitate sounds that you hear, such as a human or a parrot imitating the sound "sit." Currently, only vocal learners have been found to have forebrain regions dedicated to vocal learning and production of these learned vocalizations. Vocal non-learners only have been found to have non-forebrain vocal regions, which are responsible for the production of innate vocalizations.
Jarvis is studying hummingbirds and their vocal structures. Hummingbirds are a particularly good model to study because they have the ability to imitate sounds and pass them down through generations. The objective of Jarvis' study was to determine how the vocal learning behavioral trait and associated brain structures evolved.
Jarvis utilized vocalizing-driven gene expression to identify vocal brain structures in vocal learning and vocal non-learning species. To date, he have used this approach in three vocal learners--songbirds, parrots and hummingbirds--and has found that they each contain seven very similar brain structures. If, according to the current dominant hypothesis, vocal learning evolved independently in all six vocal learning groups within the past 65 million years, then the striking similarities in brain structure of at least the three avian groups suggests there are strong epigenetic constraints on how vocal learning can evolve. Jarvis is trying to determine if this hypothesis is correct, or if there really was a common ancestor with vocal learning and other groups lost them through evolution. (Date of Image: Unknown)