Seasonality / periodicity

Photoperiodicity:

Birds can be seen as ultimate robots.

Advantages:

  1. Guarantee appropriate sequences in successive events of the temporal program.
    Ex. Morning and evening peaks of feeding activity.
  2. Anticipate future demands- readiness
    Ex. Body temperature, and activity, breeding seasons.

A book called the ‘Dictionary of Birds’ in 1985 has a figure where the chaffinch activity was documented.
* The idea is that you record the activity of a bird over 24 hours.
Endogenous: not learned: their rhythm drifts (its not normally 24 hours). Its in effect a ‘free-running’ rhythm. Its not quite a 24 hour period, a bit less.
- Zeitgeber: light regime causes the rhythm to occur again.
- Does it matter when the zeitgeber occurs to if it works?

Rhythm occurs because of the pineal gland. It is not the light sensor, like it is in reptiles. The pineal gland produces melatonin. Production of melatonin has a daily rhythm.

Red, orange and yellow light is effective at getting their testes larger (Benoit 1950).

Types of light regimes:

  • 12hours of light per day: 12:12
  • or 6:6:6:6
  • or 4:4:4:4:4
  • or 3:3:3:3:3:3

Males grew their testes best at a 3 to 3 rhythm.

Starling with different testes throughout the year:
When kept for 48 months at circ-annual rhythms it messed up throughout the year. Ie. Every day looks like the previous day.: Male starlings have certain times of the year that they grow their testes. This persists even if they don’t know what time of the day it is.

Old world warblers breed in central Europe and over winter in the Congo. Fly over the rock of Gibraltar and then turn left and fly to their destination in the Congo. When they return they fly strait north. Use an inc blotter on birds feet and try to find what direction birds are flying in. Birds kept in a cage in Germany orient themselves in the same direction as all the other wild birds. Direction of orientation is endogenous. Birds trapped in a cage in Germany when they should turn left, show unique directional preferences. Same with when birds should fly north. AFTER Gwinner and Wiltschko 1978, 1980).

We know a lot about orientation in birds, but we know nothing of navigation.

By Rob Nelson


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