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Hummingbird studies raise questions about birdsong evolution



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Hummingbird studies raise questions about birdsong evolution 
http://www.eurekalert.org/releases/du-hsr073100.html


Contact: Monte Basgall
     monte.basgall@duke.edu
     919-681-8057
     Duke University 

DURHAM, N.C. -- In a collaborative study, American and Brazilian 
scientists have discovered that hummingbirds, parrots and songbirds 
orders of birds that are evolutionarily distant from one another have 
evolved remarkably similar brain structures in order to learn to sing. 
The finding, reported in the Aug. 10 issue of Nature, will not only 
help understand the evolution of song in birds, but also offer insights 
into language in humans.  

According to Duke University Medical Center neurobiologist Erich 
Jarvis, the paper's lead author, while most of the 23 orders of birds 
can vocalize, like the rooster that crows, these vocalizations are not 
learned but are genetically hardwired sounds. Only three orders of 
birds the songbirds, parrots and hummingbirds have the ability to learn 
songs from their adult tutors and repeat them in the right context, 
said Jarvis. This type of vocal learning is very similar to the way 
that humans learn to speak.  

Surprisingly, these singing birds are not closely related to each 
other, and in fact have close relatives that cannot learn song, he 
said. Despite their evolutionary distance, the new research indicates 
that hummingbirds use the same seven structures in the brain that 
parrots and songbirds use when they are singing their learned 
vocalizations structures that aren't even present in non- vocal 
learning orders of birds.  

The finding raises the evolutionary question of whether the three 
orders of birds developed the ability to learn song independently, and 
each time developed similar brain structures to serve this purpose. 
Alternately, there may have been a common ancestor with the ability to 
learn song, and only a few of the descendants retained this ability 
along with the specialized brain regions.  

Jarvis said that all the evidence supports the former explanation (that 
vocal learning developed independently three times) and points to 
another example of independent evolution the similar development of 
wings from limb structures in pterosaurs (ancient flying dinosaurs), 
bats and birds.  

"The reason why wings evolved in a similar way is because there is an 
environmental constraint, the center of gravity, placed on how animals 
can fly," he explained. "Here, I think there is an interaction between 
the environment and the brain, and Mother Nature has a basic 
constraint, even instructions, on how you can develop brain structures 
for a complex behavior such as vocal learning."  

In applying the bird findings to mammals, Jarvis pointed out that, like 
the bird family, mammals have only a few members who demonstrate 
learned vocalizations humans, bats, whales and dolphins. The 
evolutionary implications of the bird research may impact the study of 
how and why these few mammals have developed the ability to learn 
speech or sing.  

Jarvis and the other lead collaborator, Claudio Mello of Rockefeller 
University, gathered much of their data for this study in Espírito 
Santo, Brazil, where a living museum and nature reserve of the Atlantic 
Tropical Forest dedicated to hummingbirds was established. They 
observed birds in their natural state, using binoculars, video cameras 
and sensitive audio recorders to record natural hummingbird behavior 
and song complexity. A few of the birds were captured and their brains 
were studied to define the regions that become activated while singing. 
 

                                                                        
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Collaborators on the study were Sidarta Ribeiro from Rockefeller 
University and Maria Luisa da Silva, Dora Ventura and Jaques Vielliard 
from the University of Sa Paulo in Brazil. 
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-- 
Charles W. "Will" Cook                  w 919-660-7423
http://www.duke.edu/~cwcook            cwcook@duke.edu
Box 90340, Biology Dept., Duke Univ., Durham, NC 27708