Interdisciplinary Program in Neurocience

1
Lateralization of magnetic compass orientationin
a migratory bird
Interdisciplinary Program in Neurocience Eye
Movement Vision Research LAB Hwang, Jae Won
2
Lateralization of Birds Brain

• In Birds,
• Fibres of the optic nerves cross over completely.
• Interhemispheric commissures are comparatively
  small.
• As a consequence, visual input from the right eye
  is predominantly processed by the left hemisphere
  and vice versa.

3
Studies with monocular birds -1

• A division of function btw hemispheres
• The left eye/right hemisphere is specialized for
  geometric aspects of visual cue and novelty.
• The right eye/left hemisphere predominantly
  process object vision.

4
Studies with monocular birds -2

• A superiority of the left brain hemisphere in
  processes involving flight control, navigation
  and homing
• Monocular birds using their right eye performed
  consistently better than those using their left
  eye.
• Under overcast conditions, the difference btw two
  groups was markedly increased. ? possible
  involvement of the magnetic compass

5
Magnetic Compass Orientation

• In birds, magnetic compass orientation is based
  on light-dependent processes assumed to take
  place in the eyes.

6
European Robins

• Robins are small birds with a body length of
  14cm. They have a distinctive red face and
  breast, and brown wings and back.
• For the monocular tests, one eye of the robin was
  covered with a cap so that light could reach the
  other eye only.

7
Orientation Behavior
a. Binocular control b. Monocular left eye c.
Monocular right eye d. Monocular right eye in a
magnetic field with the vertical component
inverted
8
Orientation Performance
ab the mean heading of two recordings. rb
vector length, indicating how well the headings
of two tests coincide. rcos(?a/2)
9
Conclusion

• Being forced to use their right eye only did not
  adversely affect the birds ability to orient
  with the help of their magnetic compass.
• Birds with monocular use of their left eye failed
  to orient, which implies that they were not able
  to derive the relevant directional information
  from the geomagnetic field.