Inttranews Special Report: Birds, brains and learning
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Language is presumed to be the
most distinctive characteristic of human beings, yet
the capacity for communication by sound is far from
being exclusive to Homo Sapiens. Among the most familiar
yet least-known forms of communication in other species
is that of songbirds. Michael Beecher and Eliot Brenowitz
of the University of Washington have proposed that
our understanding of how we acquire language would
be considerably enhanced by greater research into
how birds learn to sing. So is music truly the universal
language? Inttranews decided to find out more.
Beecher & Brenowitz We tend to
be agnostic on the question of whether birds are self-aware.
But different individuals certainly show signs of distinctive
Inttranews Most of the research on songbirds
has been restricted to zebra finches and white-crowned
sparrows: why have so few species been studied?
Beecher & Brenowitz Partly for
practical reasons, and partly for historical reasons.
Zebra finches are a "pet store species"
which can easily be bred in captivity. This makes
them very amenable to developmental studies that require
the ability to study birds from hatching. White-crowned
sparrows are a wild species that were first studied
for song behavior by Dr. Peter Marler, one of the
pioneers of the birdsong field. He was located at
U.C. Berkeley early in his career and the white-crowned
sparrow is a common species in California. In addition,
they sing one only song type, which makes their songs
tractable to study. Early in his studies Marler found
that white-crowns have geographic song dialects, analogous
to speech dialects in humans. This observation attracted
widespread interest. Finally, white-crowned sparrow
chicks can be collected in the wild but reared in
captivity, which allows one to conduct studies of
their song learning.
Inttranews What is the "technical"
distinction between birds that call, and birds that
Beecher & Brenowitz To some extent
this is a semantic distinction. Calls are generally
regarded as being short in duration (i.e., less than
1 sec) and unlearned. Songs, on the other hand, are
viewed as being longer in duration and learned. But
zebra finches and other species have been shown to
learn some of their calls, and
birds in taxonomic groups other than the "songbirds"
produce songs that they don't need to learn.
Inttranews Is there any genetic distinction
between the two?
Beecher & Brenowitz There are
sure to be genetic differences between bird taxa that
learn to sing and those that don't, but at this point
we don't yet know which specific genes might differ.
No one has yet definitively identified a "song
Inttranews Are there any genetic or other
differences between songbirds and birds that mimic
Beecher & Brenowitz Again, we
just don't know enough about bird genetics at this
point to answer this question.
Inttranews There are radical differences between
the song-learning patterns of different bird species:
some learn very early, some learn all their lives.
How do you explain these differences?
Beecher & Brenowitz An excellent
question and one that we believe deserves much more
attention. We believe that there is a continuum between
species that only learn songs very early and those
which learn all their lives, with variations between
these two extremes. A bird's song learning program,
as we refer to it, evolves in response to the specific
ecological factors to which it is exposed. For example,
some species may have evolved the ability to learn
songs throughout life so that they can increase the
total number of different songs they sing and so indicate
to potential mates how old they are. A female might
choose to mate with an older male because he has proven
survival ability which might be passed on to her offspring.
Other species of birds learn new songs as adults but
replace old songs with new songs so that the total
number of songs doesn't change with age. In such species
adult song learning may enable birds to learn songs
from the set of other birds who have neighboring territories
each year and so be able to use those shared songs
in vocal interactions at territory boundaries. On
the other hand, in species that don't learn new songs
as adults, such as the white-crowned sparrow, it may
be that the risk of making mistakes in song learning
is greater than the benefit.
Inttranews Just as a child born to Chinese
parents will equally as easily learn Armenian if brought
up in that language environment, does a bird of one
species when brought up in another environment develop
the song patterns of that species?
Beecher & Brenowitz If young
birds are given the choice between song of their species
and song of another species, they typically learn
the song of their species, which suggests that there
is an innate predisposition for such "native"
song learning. But if young birds are only exposed
to song of another species, they will often learn
that other species' song. This is especially true
if the non-species song tutor is a live bird.
Inttranews Is there any parallel between the
way birds learn to sing and the way human beings learn
Beecher & Brenowitz There are
several parallels between human speech learning and
bird song learning. In both groups the young typically
need to hear the vocalizations of adult members of
their species; form a perceptual memory of those vocalizations;
have an innate predisposition to learn the signals
of their species; typically learn better when young
than when mature; go through an initial babbling-like
phase and progressively improve their vocalizations
until they produce a good copy of the "tutor"
signal; and need to hear themselves while they're
rehearsing their vocalizations in order to improve
Inttranews Do songbirds always produce the
same limited pattern of song, or are there infinite
variations? If so, which species?
Beecher & Brenowitz It depends
on what species you're considering. On the one hand,
white-crowned sparrows learn one song type when young
and then sing that same song their whole lives. On
the other hand, in species like the brown thrasher,
the bird seems to improvise novel songs while it is
singing and may have an unlimited repertoire of song
variations. Many species lie between these extremes.
Inttranews Are there genetic differences between
songbirds that vary their song patterns and other
birds? i.e. are they more evolved?
Beecher & Brenowitz Again, we
know too little about the genetics to answer this
question at this time.
Inttranews Is there any connection between
birdsong and the species' immediate environment? For
example, are there more songbirds in tropical climates?
Beecher & Brenowitz The majority
of songbird species (ca. 80%) breed in the tropics.
One connection between song and the immediate environment
is in the ability of the acoustic features of song
to transmit through the environment so that they may
be detected by listeners at typical distances that
separate birds. In forests, for example, there is
greater reverberation of sounds off trees and leaves
and so forest-dwelling bird species tend to avoid
rapid changes in song structure (as in trills). In
more open habitats like marshes or grasslands, however,
there is little reverberation but more wind turbulence
which can produce low frequency distortions. Species
in these open habitats therefore typically have rapid
changes in song structure. Another unexplained difference
between tropical and temperate-zone species is that
in tropical birds typically both male and female song
(sometimes they duet), whereas in temperate-zone species,
usually only the male sings.
Inttranews What factors influence those birds
that learn a new group of songs each year?
Beecher & Brenowitz Learning
new songs each year allows a bird to learn the songs
of males that occupy adjacent territories and engage
in song matching interactions. Also, if the total
number of songs a bird sings increases each year,
this can provide information about his age and therefore
survival ability to potential mates.
Inttranews There has been much discussion
among cognitive ethologists that birds have individual
personalities. What is the state of current thinking
There has been much discussion recently about the Foxp2
"language gene" that we share with a number
of species. What is the state of current thinking and/or
Beecher & Brenowitz
Foxp2 is expressed widely in the avian brain, including
in regions that control song learning and production.
But the patterns of expression are not selective for
the song regions, and the 5 amino acids that are affected
by human foxp2 mutations that affect speech are not
present in the avian foxp2. Foxp1, on the other hand,
is expressed with a higher degree of selectivity in
song regions of the bird brain, it is sexually dimorphic
in expression in species where only males sing, and
its expression varies seasonally in species that sing
a lot during the breeding season but less or not at
all outside the breeding season. Foxp1 may therefore
be the more interesting gene with regard to song learning.
Inttranews What other traits do we have
in common with songbirds?
& Brenowitz Vocal behavior in both birds
and humans is regulated by a hierarchy of regions in
the brain, with extensive integration between auditory
and vocal motor systems. Also like us birds have good
spatial memory and can count.
In cognitive or behavioural terms, can your research
be applied to language learning or more generally to
brain development among human beings?
Beecher & Brenowitz There are several
possible answers to this question. First, the neural
centers controlling song in songbirds, which exhibit
plasticity throughout the lifetime of the animal, represent
the best vertebrate model system for studying language
learning and learning in general. Second, the diversity
of song learning systems we have noted suggests that
learning programs can diversify very rapidly in evolution,
which ultimately should make the bird song system an
even more illuminating model system. Third, recent research
is indicating that purely social factors have a much
larger impact on song learning than was originally appreciated.
In some cases, song learning revealed in field studies
or in lab studies with live tutors gives results quite
different from those derived from the classical laboratory
approach in which tape-recorded song is passively presented
to a socially-isolated young bird. That’s why
we call social factors the "wild card" in
song learning (they can change the results completely);
see next answer for more.
What direction would you like your future research to
take, and what experiments would you like to carry out?
Beecher & Brenowitz We are
doing experiments on social factors in song learning.
Previous research has suggested that the young bird
needs more than passive experience with the song of
an adult bird, that he needs to experience actual singing
interactions. Our recent experiments suggest that two
kinds of singing interactions are key events determining
which songs the young bird learns: (1) direct singing
interactions the young bird has with an older song "tutor"
and (2) singing interactions he overhears. Surprisingly,
the latter class may be the more important of the two.
To gain further insights into these social processes,
we are developing a "virtual tutor", a computer
program that presents digitized songs to a young bird
in a manner simulating natural singing interactions.
We are also studying how birds use their different songs
in song interactions in the field (see "song fights",
Science News Dec 18/25, 2004).
And now for the million-dollar question: why do birds
Beecher & Brenowitz
The simplest answer is that birds sing to convey information
to other birds. Relevant information includes species
identity, individual identity, gender, possession of
a territory, membership in a kin or social group. The
two main functions of song are to declare a territory
and to attract mates.
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