Bird Song Flashcards
What is bird song?
musical phrases uttered by some birds, whales and insects, forming a recognizable and repeated sequences and used chiefly for territorial defence or for attracting mates
Zebra finch
important breed for bird for investigation of song
australian, easily kept and bred
highly social, no distinct breeding season
development takes around 4 month, juvenile birds hear adult songs all time
Levels of organisation
notes combine together to make syllables
notes have lots of different frequencies so sound more squeaky
syllables and notes form longer sequences- motif
if bird is interrupted it finished syllable- syllable is basic unit
in zebra finches motif is fixed in form for a particular male
but number of motifs is variable as are introductory notes and notes between motifs
Swamp sparrow
been important recently in study of mirror neurons
more simple monogram than zebra finch
have a library of different songs
Song production
syrinx 4-6 muscles either side
sound is produced when air is expelled
muscles shape the way the air flows through and therefore the sound is produced
often asymmetrical- one side used in one part of song and other used in another
in canaries each syllable coincides with cycle of inspiration and expiration
Song Development
most temperate species have development in 3 distinct phases
1 sensory- hears songs of tutors
2 sensori-motor- plastic song, often mix different songs
3 crystallization to mature form
Thorpe- need for tutors
isolation experiments
chaffinches need to hear adults songs in 1st spring; do not sing until next spring
later in other species- shown young bird must hear own immature songs
not many animals can learn vocalizations
zebra finches breed all the time so hear songs all the time- therefore stages of development are less distinct
canaries and starlings develop new songs every year
Brain nuclei and singing
1 group process auditory info
1 group produces song motor program in adult
1 group involved in song development in juvenile
HVC and RA belong to all 3 groups
birds have smooth veins
RA nearer to motor neurons that control muscles of syrinx than HVC
Area X back of brain involved in learning song
Hierarchical arrangement
HVC packed full of neurons- some active in some syllable some in others
HVC has direct connection with RA
During song, spike rate in individual HVC neurons increases and decreases during particular syllables
Individual RA neurons produce discrete bursts of spikes coinciding with specific series of notes
In RA but not HVC- spatial organisation corresponds with particular muscles
stimulating neurons in HVC affects current and following syllables
stimulating RA has no knock on effect
HVC has sensory as well as motor properties
in an anaesthetized or sleeping zebra finch, many HVC neurons respond well to recordings of bird’s own song but not to songs of other zebra finches
Peters et al (2008) mirror neurons
singing sparrows trigger each other
HVCra neurons have no auditory responses- active when bird is singing but not when other birds are
HVCx have both sensory and motor responses- neurons spike during a particular song and to a record of that song
but does not respond to recordings of preferred song while bird is actually singing (motor properties switch off sensory properties so that it is no longer listening)
HVCx neurons carry a copy of song command that goes to area X
this may allow comparisons between expected and actual sound during singing
HVCx neurons respond to records of other birds song that resemble song type that is preferred
could be a mechanism for decoding meaning of others song
can compare expected song with what is actually produced- important for development
Development and learning
LMAN, DLM and Area X needed for normal development
area X could be site of comparison between sound of song and and the command issues by HVC
in adults neurons in HVC, area X and LMAN respond specifically to records of birds own song
selectivity arises gradually in development
in young birds these neurons excited by many sounds including reversed songs
when song crystallizes all neurons prefer birds own song
during development, structure of nuclei change
large number of neurons die and connections are blocked
in juvenile zebra finch, LMAN very much like HVC in adult
babbling doesn’t need HVC
learning often involves animal trying alternative and finding which works best
juvenile birds babble- needs LMAN
like HVC it connects to RA and area X
In adult if HVC is inactivated by drug TTX the bird babbles until the drug wears off
LMAN may be responsible for trial and error
only final programme for song sent to HVC
Bolhuis and Gobes (2007)- NCM`
It has also been suggested that other areas of the brain play an important role. When an adult zebra finch was exposed to its tutor’s song there was an increased activation in the neurons in the caudomedial nidopallium (NCM).
The same study also found that lesioning the NCM disruption recognition of the tutor’s song but not the adult bird’s ability to produce song. These findings together suggest that the neural representation of the tutor’s song may be held in the NCM. Having this neural representation of another bird’s song allows the growing bird to store and compare the song they learnt from in order to make their song as effective as possible. Thus, birds of the same species will sound similar.
testosteron
The final stage is the process of crystallization where the selectivity of neurons in HVC, area X and LMAN rises to the point where the neurons prefer only the sound of the birds own song. This is likely due to the rising level of testosterone. Throughout this process, there is great structural change in the nuclei involved in song development and production. Neurons die and synapses are pruned. Testosterone has previously been found to stunt the growth of neurons (Ehrlich et al, 2006). If the level of testosterone influences which and how many neurons die, each that carries specific information about song production, then, individual differences in levels of testosterone will affect the variability of song between birds of the same species.
