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canario timbrado

Song Learning in the Canary II

   
 

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:

  1. 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.
  2. 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.).
  3. 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.
  4. 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.)


 

   
   
© Vicente Jerez Gomez Coronado
© Translation Sebastian Vallelunga

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