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Inttranews Special Report: Birds, brains and learning

By webmaster@inttranews.net
http://www.inttranews.net

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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.

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 sing?

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 learning" gene.

Inttranews Are there any genetic or other differences between songbirds and birds that mimic speech?

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 to talk?

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 their production.

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 and/or research?

Beecher & Brenowitz We tend to be agnostic on the question of whether birds are self-aware. But different individuals certainly show signs of distinctive "personalities."

Inttranews 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 research?

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?

Beecher & 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.

Inttranews 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.

Inttranews 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).

Inttranews And now for the million-dollar question: why do birds sing?

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.

Website links:

http://faculty.washington.edu/beecher/

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