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Hummingbird studies raise questions about birdsong evolution
- To: carolinabirds@duke.edu
- Subject: Hummingbird studies raise questions about birdsong evolution
- From: "Will Cook" <cwcook@duke.edu>
- Date: Mon, 14 Aug 2000 13:48:32 -0400
- Priority: normal
- Sender: carolinabirds-owner@acpub.duke.edu
------- Forwarded message follows -------
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.
###
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.
------- End of forwarded message -------
--
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