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By Vicente Jerez Gomez Coronado
Translated from the Spanish by Sebastian Vallelunga
NEUROLOGICAL CONTROL IN LEARNING
Although the song of the canary is executed in
the song organ "the syrinx" it is the brain in which the contents
of the stable song resides, with its syllabic composition and concrete
musical norms and where control over the song execution on the part
of the syrinx is located, as we shall see.
In 1976, Fernand Nottebohm, specialist in animal
behavior and neurogenesis at Rockefeller University in New York,
identified groups of differentiated cerebral cells which control
song in canaries. These cells are distributed in a major center,
called the superior vocal center (CVS), which sends axonal elongations
to another center called the robust archistriatalis (RA); this,
in its turn, sends other axonal elongations to the center of the
hypoglossal cranial nerve which controls the muscles of the syrinx.
Both centers are situated in the frontal lobes of the canary which
is where complete learning behavior is controlled. The CVS seems
to be responsible for identifying, memorizing, and producing song;
effectively, this center functions to identify perceived songs,
functions as a song model memory in order to imitate it, if the
bird is male, or in order to recognize and identify its family or
partner, if the bird is female. This song information, stored in
the CVS, is translated by means of the axonal elongations to the
RA center which is responsible for causing the motor dexterity in
the execution of the song by means of the hypoglossal cranial nerve,
which communicates with the muscles of the syrinx.
It has been proven that these centers are larger
in those canaries with more complex songs than in those who have
simpler ones; they grow in size with the administering of testosterone
and in the spring when the levels of testosterone are at their highest;
in the same way they are larger in males than in females; on the
other hand, they diminish in size after the reproductive stage at
which time there is a return to unstable song and blood testosterone
levels fall drastically.
It has been proven that the survival of regenerated
neurons located in the CVS depends on the presence of sufficient
levels of testosterone, enlisting these neurons by means of a neurotrophic
factor derived from the brain (FNDC); we see that their survival
depends on the time the canary spends singing, and the use of the
motor circuits related to sing stimulate the freeing of the FNDC,
affecting in this last case more neurons of the RA center. This
also confirms that the hearing of sounds helps to unfold and to
give power to the auditory circuits involved in the learning of
the singers.
The important fall in the level of testosterone
during the first months of the first year of life from May to June,
coincides with the first molt and a staking in the growth of the
size of the song control centers, which recuperate in the next months
paralleling a recuperation of the testosterone levels which reach
a maximum during November. All this happens during the plastic song
stage associated with the important learning process. The size of
the song centers, as has been stated, reach their maximum during
spring when testosterone levels are highest.
From the second year onward and with annual periods,
at the beginning of the breeding season, during the molting period
which follows, principally in August, the neurons of the song regulatory
centers undergo a process of regression and a great number die causing
a decrease in the size of the centers, coinciding with the important
fall of testosterone levels. At this phase of regression of the
centers there also occurs a regeneration, by means of a process
of neurogenesis with an incorporation of new neurons, which reaches
a peak in November, when testosterone returns to very high levels.
This process repeats itself each year in the same way.
Coinciding with these moments of crisis of falling and recuperation
of testosterone levels and a regression and recuperation of the
cerebral centers which control song, there is produced an instability
in and modification of the song, wherein the bird may lose, incorporate,
or modify song syllables. The song becomes stable once again from
November to May, when the process of regeneration of the song centers
is also stabilized. These ups and downs in the size of the cerebral
centers are not seen in other songbirds and the original learned
song endures throughout life.
Given the parallel seen between the capacity to
learn and emit complete song and the size of the cerebral centers,
caused by the action of testosterone during the stage of subsong
and even more fundamentally during the phase of plastic song, there
remains the manifestation of song dependence with respect to correct
development of the cerebral centers and, in its way, the availability
of an adequate testosterone level at these times.
Also with an annual periodicity, in January, there
is another important drop in blood testosterone levels of an unclear
significance, for which there is no accompanying song instability
nor a decrease in the size of the song centers, perhaps it signifies
an important increased consumption in this hormone in the fabric
of the process of unfolding the sexual characteristics in preparation
for the breeding season (A bird I own just went through this January
period; although he had a limited song and some expected elements
of his strain's typical song were missing, he did pick up one element
and rearrange others at this time. Perhaps the January period acts
as a sort of last minute period of adjustment before the breeding
season in cases when the song is incomplete for whatever reason
after November--trans.).
LEARNING AND THE IMITATION OF AN ADULT MODEL
It seems logical to think that, if canaries have
the capacity to learn song by imitating the model of adult males,
and this is the procedure that these birds follow when they live
free in nature, since they live with and learn the song of their
father and other adult males within the group, our canaries should
also learn to sing in imitation of an adult male of quality song,
seeking nature's example as our guide. This is the criterion of
very good breeders like Arcadio Pavon Macho, from the city of Cazalla
(Seville), who uses a tutor with his young birds so these will learn
to pronounce the notes well, always given that the young are genetically
disposed toward good voice. The tutor is left in the relative freedom
of the flight, together with the young males, until these are placed
into the individual cages (mid-October to mid-November); the tutors
are "complete" canaries which have not "been covered" nor bred to
excess (he seems to mean a male bird with a high degree of machismo,
not having been intimidated by other more dominant ones nor worn
out with breeding--trans.), because such birds keep a higher quality
song. Once the young birds are removed from the flight, the tutor
becomes unnecessary. It is hypothesized that song is of higher quality
when it is learned from an excellent example and song defects are
avoided, having been previously weeded out in the process of the
selection of tutors.
Other expert breeders, like Joaquin Sandua Sanchez,
of San Pedro de Mieres (Oviedo), maintain, without exception, the
criterion of not using tutors so that the songs exhibited by the
young are spontaneous manifestations of their genes and not a counterfeit
learned expression instead; in consequence, the selection of example
birds with better song is actually the selection of example birds
of better genotypic quality. This is not to say that two canaries
with the same genetic endowment tend to exhibit an identical song,
rather the song, like the phenotypic model it represents, results
from the interaction of the genes and the surrounding ambiance,
in the fullest sense (other audible sounds, light level, diet, temperature,
neighbors in greater or lesser numbers, the disposition of testosterone
levels during plastic song, etc.), and it is almost impossible to
say they will be similar when the ambient conditions seem to be
the same for two birds. This method of learning without a tutor
is applied until a fixed line is determined; afterwards it gives
the same results weather one uses a tutor or not, so long as the
object of selection has been realized and the line firmly fixed.
Moreover, experience also demonstrates that a canary who elaborates
a composition or song without a tutor has a higher capacity for
improvisation, and in the same way his song will not be repetitive,
changing from one performance to another. It is useful to house
the young males by family groups, which will have a similar genetic
endowment and have songs which should be of similar characteristics
and avoid or limit the influence of other groupings of young males
of different lines, housed in adjoining flights, that can hear and
influence each other, against which one may use a radio which works
as an acoustic barrier.
An intermediate criterion, one more eclectic, is
to use a tutor in the flight, but only until the beginning of the
molt in July and the tutor stops singing; in this way the young
may unfold the song learned according to their own genetic make
up during the rest of the summer and autumn. A fourth possibility,
also used by some breeders, is to employ various tutors of different
song, all placed in the flight with each young male learning the
song he likes the best or a mixture of them all. Other breeders
use a mixed system: in order to draw out new floreos and new quality
songs, they breed a few pairs away from the others without using
tutors; if some of the young display new floreos or new songs of
quality, these are used as tutors for the majority in the next breeding
season.
There exist experimental studies conducted with other songbirds,
like the pinzon cebra (zebra finch?--trans.), from which one may
extract the following findings:
- A single young bird raised in captivity with his father present
imitates him almost exactly, but, when various young males are
raised with an adult male present, each one converts, in his own
way, his brothers into tutors and diminishes his imitation of
the adult model: the greater the number of young males together,
the smaller the number of imitated syllables and the shorter the
duration of the song learned. The young born later learn from
adults quicker than older siblings, relatively speaking, and they
have a more complete imitation.
- The young can learn from a song model presented to them in a
recorded medium in a song cage, but an excessive "playback" of
the model reduces imitation behavior by 33%. This restriction
of imitation selectively affects certain concrete syllables not
being produced at random; these can be syllables almost all of
the other young birds imitated or others which almost none did
(If I understood correctly, this means a young bird taught to
sing using a recorded medium which is repeated overly frequently
will permanently leave out a part of the song from his repertoire
due to the less complete learning caused by the 33% reduction
in imitation behavior--trans.).
- The raising of young in social isolation, that is to say, alone
and without hearing adult song models, can give voice to an improvised
song which, although atypical, will include many normal sounds.
However, this capacity for improvisation does not seem to manifest
itself when even a small amount of imitation is possible due to
limited exposure to an adult model.
- When the young hear the song of another male outside of their
cage, a male whom they cannot see or interact with, imitation
of his song is scarce or absent.
There are no experiments, although they are being
worked on, which have dealt with using various song models at the
same time.
The light shed by this data, in relation to the
practices used in canariculture, allows us to state the following:
1) Effectively, the young bird caged with his father or another
adult male imitates his song in an almost complete form. The imitation
is must less complete when many young birds share the same flight
and young birds born later learn the adult's song at a younger age
than the older ones. The use of recordings when the young are in
individual song cages leads to an leads to an almost complete imitation,
paradoxically, if the young hear it seldom, no more than two or
three minutes a day; if it is played more abundantly, the imitation
will be incomplete.
2) When no adult model is present to imitate the
young will improvise an atypical song, but one with characteristic
syllables. In this case each young male will serve as a tutor to
the others.
3) The use of a radio as background, playing all
day long, may produce two effects: first, to stimulate the song
auditory routes, including the CVS; second, to serve as a superabundant
auditory stimulus, succeeding in reducing the capacity for imitation
in young birds who hear it, which would be an aid for the breeder
that pursues the line that the young birds should not imitate those
models which they hear. It is easy to understand the stimulating
action of the sounds on the song auditory routes, placed in a location
where there is a lack of stimulus, the previously referred to routes
will atrophy in the same way that a deaf person's speech centers
and routes do limiting the ability to speak correctly.
4) Excessive exposure to sounds, like the use of
a radio in a continuous way or the learning to sing in the presence
of a large number of young birds, may put into play processes of
selectivity in the attention of the young in terms of imitation,
accepting some models and rejecting others. This may account for
the wide range of sounds and songs encountered in singing birds,
in the natural setting as well as in captivity.
CONCLUSIONS
There are many questions related to the learning in song canaries,
and this keeps open study and experimentation, but we may draw the
following conclusions:
The characteristics of faculty and timbre of voice,
fundamentally depend on the anatomic conformation of the phonetic
organ of the canary, which is determined to a great extent by genotype.
The musical composition or song of the canary forms
part of its phenotype and, in consequence, results from an interaction
of the genotype and the ambient medium, in the widest sense.
Although canaries preserve the capacity to learn
new syllables throughout the year, it is during the plastic song
phase or the critical period of learning when they have a greater
capacity; in consequence, the shortening of this period, the acceleration
of the onset of sexual maturation by means of individual caging
or giving excess testosterone, can lead to a syllabic poverty of
the song.
We fail to recognize many factors relating to ambience
that can influence song learning, as the concrete aspect of phenotype
that it is; we may place these into two groups: those which are
related to auditory stimulus which may or may not serve as models
and those which relate to the availability of optimum testosterone
levels.
It is not accepted that in a generalized form learning
with a tutor yields a song with greater syllabic richness or more
musicality, although it is clear that tutored birds sing like their
tutors, given the capacity for imitation of them. Learning without
a tutor can lead to a song which, at least, has as much syllabic
richness and musicality as that learned from a tutor, can be an
aid in obtaining new floreos and songs which are a reflection of
an adequate genotype, permit a genetic selection which is more certain;
gives a better capacity for improvisation; on the other hand, using
this system there is a larger risk of producing song of lower value
with defects in its execution. One does not, however, have the inconvenience
of using a tutor in a line, once it has been firmly fixed.
(All of the material on annual song learning
causes one to wonder what the adaptive advantage is for male canaries
to have to relearn part of their song each year when most songbirds
use the same song throughout life once it is learned in youth. Is
it that some songs are more helpful in defending a territory or
attracting a mate in some years more than others on the Atlantic
islands from which the original birds come? Does something like
winter weather pattern determine spring feed quantities and therefore
make it more, evolutionarily speaking, advantageous to attract a
certain sort of female with a preference for one type of song over
another? Does the type of song learned by males in any given year
have a certain bent that most males follow? Is the type of song
a subtle statement read by females about the male's health and probable
abilities as a father provider? Is the relearning simply a random
affair in which certain individuals change songs a lot and others
a little without reason, and yet, if this is so, how did this characteristic
survive natural selection among canaries when it is unknown among
other songbirds?--trans.)
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