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Chapter 2: Understanding the Proximate and Ultimate Causes of Bird Song
DIFFERENT SONGS: PROXIMATE CAUSES
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Peter Marler was a fledgling limnologist who found that different populations of whitecrowned sparrows often have distinct dialects depending on their location
One proximate explanation for the dialect differences was a genetic difference between
locations that could affect construction of nervous systems
Marler and colleagues took eggs from the nests and hand reared them and kept these
birds isolated from singing birds
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This pathway suggests that these brain elements exert control
over singing behavior
If neural messages from the RA cause songs to be produced then the experimental
destruction of this center or surgical cuts through th enerual pathway leading from the RA
to the NXIIts should have devastating effects on a bird’s ability to sing the RA does
have a role in song production so in bird species like the white-crowned sparrow, in
which males sing and gemales do not, the RA should be larger in male brains than in
female brains and it is
Destruction of the lateral magnocellular nucleus of the anterior nidopallium (IMAN) does
not strongly interfere with an adult zebra finch’s ability to sing its learned song, but if the
operation is performed on a juvenile bird before it has acquired a mature song then the
bird will fail to sing a normal song in adulthood
IMAN should be much reduced orabsent in bird species that sing but do not learn their
songs, which is true
An analysis of currently available studies on the relation between the volume of the HVC
and the size of the male song repertoire within a species shows that overall, the two
variables are significantly correlated: a male of a given species with a realtively large
repertoire usually has a larger HVC than other, less gifted members of his species
Two groups of male songbirds—1 permitted to shape its song repertoire through learning
and the other that is raised in acoustical isolation
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65 mya
since the first truly modern bird appeared, or song learning originated in the ancestor of
all the lineages from Psittaciformes to Passeriformes, but then wast lost three times (1) at
the base of the evolutionary line leading to the Apodiformes (2) at the base of the
combined Musophagiformes and Strigiformes lineages and (3) at the base of the lines
constituting Columbiformes, Gruiformes, and Ciconiiformes (first scenario is more
parsimonious)
In all three groups cells that form the caudomedial neostriatum activate their ZENK
genes when individuals are exposed to the songs of others, which contributes to the
processing of song stimuli
When these birds vocalize, other brain centers respond with heightened ZENK gene
activity

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There is considerable, but not perfect correspondence in the locations of these distinctive
song production centers

THE REPRODUCTIVE BENEFITS OF SONG LEARNING
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What do birds gain by having a distinctive vocal message (learned or unlearned)
o One hypothesis is that the distinctive vocalization conveys information about
species membership
o One benefit to males who sing differently than other species may be enhanced
deterrence of competitors of their own species for territories and mates
o Rival males of the same species pose the greatest threat to a singer’s reproductive
success
New males are slower to move into territories where songs are broadcast than silent
territories, which are always the first to be invaded by an intruder
Females that rapidly locate males of their species can begin reproducing sooner with a
member of their own species, avoiding the risks of mating with members of another
species

THE BENEFITS OF LEARNING A DIALECT
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Song learning is not essential for the acquisition of a species-distinctive signal
Effective transmittance in different habitat types—low frequencies used by male satin
bowerbirds in dense forests travel further, but those in open, less cluttered forests tend to
employ higher frequencies in their versions of bowerbird song
Vocalizations differ between city and country birds as studied by Hans Slabbekoorn and
his coworkes
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The key point is that
song learning occurs when males are very young and growing rapidly
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The experimentally deprived
birds came to sing poorer copies, compared with the controls of the taped song aht both
groups listened to during their early weeks of captivity
Female sparrows can be primed hormonally to respond with a tail up precopulatory
display to male songs they find sexually stimulating
The research shows that males able to learn their songs fully and well will be rewarded
sexually by potential mates
Females spent more time by a speaker playing the directed song of an unfamiliar male or
her mate, compared to her mate’s undirected song==this preference was linked to the
properties of cels in the caudomedial mesopallium (CMM) in the auditory cortex of the
zebra finch brain by Wooley and Doupe
Other female songbirds definitely prefer the songs that are relatively difficulty to produce
Females are attracted to males that sing right up to the limits of performance
Females serins prefer males that sing at relatively high frequencies, which is another
physiological challenge for males



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