BIOL 329 Lecture Notes - Lecture 18: Inner Ear, Dactyly, Great Tit
6 May 2018
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Lect 18
Hearing
Distance and direction of sound sources is identified by:
A) horizontal angle (azimuth) relative to the direction of the head.
B) The vertical angle (elevation) above or below the position of the head.
No external ear/pinnae. Sound goes down auditory canal to tympanic membrane. Single bone
(columella or stapes) transmits vibrations through the middle ear to the inner membrane (oval window)
in the cochlea (inner ear). Cochlea has a second membrane (round window) that allows pressure
vibrations to be dissipated. 20X Amplification. Inner ear for hearing and balance (uncoiled cochlea).
Length of cochlea varies among species (longer in predators). Sensitivity ranges
Sensitivity of ears changes seasonally. Cochlea does’t chage i size so what does? Witer: uch ore
sensitive than they are in spring. Provides increased acuity. In the white-breasted nuthatch. Great tit is
more sensitive than sparrow-hawk at low and high frequencies. Hawk is most sensitive at intermediate
frequencies.
Owl hearing: facial feathers focus sound to the ears. Horizontal plane (like other tetrapods) – timing. Can
identify vertical plane from asymmetric structure of ears. R ear – more likely to hear sound from above.
L ear – more likely to hear sounds from below. If bird flies over the source, sound is louder in L ear. Bird
rotates head and body until stimulation in symmetrical. Newly hatched chicks are deaf until second
week. Characteristics of the cochlea: predictor of the frequencies the bird can hear.
Bird brain: Pigeons exposed to black and white images – exposed to a negative image and a positive
image and was rewarded for pecking the positive shape. After training, pigeons scored 82% (humans
>20%). 7 months later, the pigeon scored almost as well (humans remembered nothing).
Clark’s utcracker: hide ,000 seeds i 500 caches – retrieve majority of seeds over winter and can
remember seed positions for over 6 months. Parrots have higher neuron count than primates per same
brain mass.
Movement: Walking (cursorial spp)
Hopping (feet together: most arboreal birds – passerines, starlings + crows – hop and walk)
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Document Summary
Distance and direction of sound sources is identified by: horizontal angle (azimuth) relative to the direction of the head, the vertical angle (elevation) above or below the position of the head. Sound goes down auditory canal to tympanic membrane. Single bone (columella or stapes) transmits vibrations through the middle ear to the inner membrane (oval window) in the cochlea (inner ear). Cochlea has a second membrane (round window) that allows pressure vibrations to be dissipated. Inner ear for hearing and balance (uncoiled cochlea). Length of cochlea varies among species (longer in predators). Wi(cid:374)ter: (cid:373)uch (cid:373)ore sensitive than they are in spring. Great tit is more sensitive than sparrow-hawk at low and high frequencies. Owl hearing: facial feathers focus sound to the ears. Can identify vertical plane from asymmetric structure of ears. R ear more likely to hear sound from above. L ear more likely to hear sounds from below.
