Birdsong

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  • Created by: Husnaa
  • Created on: 08-01-13 13:13
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  • Birdsong
    • How are bird songs researched?
      • Sonograms allow you to 'see' the sounds that make up the bird song.
        • Smallest unit of sound =Note
          • A group of notes =  syllable
            • A group of syllables makes up a phrase
              • Syntax= the specific timing and tempo of the birdsong.
    • How do birds learn songs?
      • 1st Stage: Sensory stage  Baby birds listen and learn tutors songs (don't sing themselves
      • 2nd Stage: Sensorimotor Stage Birds try out songs and using auditory feedback, learn which are good.
        • Sub-song stage: like babbling in toddlers, soft, rambling sounds
        • Plastic Song: More like adult song, recognisable as the species song, but still very variable
      • 3rd stage: Crystallisation Stage: learnt song is ingrained into birds memory, will be used many times occurs even in open ended learners
      • Seasonal Closed Learner:e.g White crowned sparrow has a separate sensory and sensorimotor stage. songs are crystallised by spring after birth i.e one year. Critical period ends just before sensorimotor stage
      • Age-limited learners: e.g Zebra- finch. Some birds breed all year round, so they have a time limit instead. the zebra-finch has a critical period of 60 days, this is both the sensory and sensorimotor stage, as these overlap, after this the song will be practiced and crystallise.
      • Open-Ended Learners, e.g Canaries. These birds can learn new songs every year. but every year they go through the same process of sensory/sensorimotor (overlapping)stages followed by crystallisation.it is still unknown whether there are sensory stages every year.
      • If bird song is only 33% imitation of tutor-song, why are tutors so necessary? (birds without tutors sing very simplistic songs.
        • The tutor teaches the song, but many of the syllables are lost in the plastic song stage
          • Also, birds  innately prefer to hear members of their own species sing.
          • Then they prefer a live tutor irrespective of species
          • Least preferred is a recorded song, but it still produces a functional song
      • How do birds recognise their own species song?
        • Some birds recognise only the syllables, (swamp sparrows) others recognise the syllables, syntax and tempo (song sparrows)
          • Song template is part innate, part learned
            • Therefore deafened birds can't sing because song needs to be matched to innate template.
              • If it is deafened  after the subsong stage, the bird can still sing, but some begin to lose their ability very soon, some within weeks
    • How are the sounds produced?
      • Syrinx and sound production
        • Air is expelled from a complex system of air sacs
          • The tympaniform membranes are vibrated by the expelled air and create the sound
        • The syrinx is located at the junction of the trachea and the bronchi
        • The syringeal muscles alter the tension of the tympaniform membrane to cause different frequencies
        • Syrinx has two almost identical halves, the right and left
    • How does the brain generate bird song?
      • Lateralisation
        • The left side of the brain is more involved with singing in many birds, similar to humans being right/left-handed, or left brain involved with creative expression
          • In some birds when the left  hyploglossal nerve is severed, it impairs singing, however if it is done early enough, the bird will learn to sing using the right side of the brain, and thus will still be capable of fully functional song.
            • Zebra finches show right-sided    dominance whereas swamp sparrows show no dominance.
      • 2 song pathways in the brain
        • Anterior Forebrain Pathway (necessary for correct song learning)
          • Area X
            • DLM (Dorsolateral  Thalamus)
              • LMAN (Lateral portion  of the magnocellular nucleus of the anterior neostriatum) Contains SONG-SELECTIVE NEURONES
                • RA (Robust Nucleus of the Archistratium)
                  • Song Production Pathway (important in vocal learning and adult song)
                    • Proof: When HCv is stimulated during singing, it causes phrase advancement, also both RA and HCv are active just before singing, therefore pacemaker for singing.
                      • In Zebra finches, this pathway only becomes active after sensory phase when bird starts singing.
                  • nXIIts (tracheosyringeal portion of the hypoglossal nucleus) Innervates the syrinx muscles
                    • Song Production Pathway (important in vocal learning and adult song)
                      • Proof: When HCv is stimulated during singing, it causes phrase advancement, also both RA and HCv are active just before singing, therefore pacemaker for singing.
                        • In Zebra finches, this pathway only becomes active after sensory phase when bird starts singing.
                  • Respiratory Control
            • DLM (Dorsolateral  Thalamus)
              • LMAN (Lateral portion  of the magnocellular nucleus of the anterior neostriatum) Contains SONG-SELECTIVE NEURONES
                • RA (Robust Nucleus of the Archistratium)
                  • nXIIts (tracheosyringeal portion of the hypoglossal nucleus) Innervates the syrinx muscles
                    • Respiratory Control
                • Proof: pathway active in  zebrafinch only during sensory phase
                  • Also, when LMAN is severed during infancy bird doesn't sing, but  lesioning during adulthood has no effect.
            • Role of testosterone in inducing singing
              • When testosterone levels are high in birds, the number of syllables they can produce are greater
              • Castrated males do not sing, but those given testosterone supplements will sing
              • Female birds that don't ususally sing can sing if given testosterone
              • Larger song nuclei (HCv and RA) = bigger repertoire of songs
                • more testosterone = bigger song nuclei
                  • Females have very small HCv and RA nuclei.
            • Neurogenesis
              • Why do the HCv and RA increase in size during certain seasons?
                • The increase in size is a result of: 1) increase in synaptic connections and 2)  neurones being added
                  • Neurones are only added at the sensory phase, thus most plasticity occurs at this stage.
              • Untitled
          • Why do birds sing?
            • To find a mate
            • to maintain territory

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