Recognition comment:
Recognises that food searching activity is more strongly controlled by access to food than light through statements such as:
- birds always anticipated food access irrespective of changes in light regime (supported by experimental evidence) OR
- If light was the stronger zeitgeber then would have seen a change in activity when the timing of the light phase changed (supported by experimental evidence)
And supporting evidence:
- Expt 1 - Introduction of PAF(periodic access to food) resulted in transient but fairly rapid shift of evening activity until much closer to morning activity showing that timing of food access is acting as a zeitgeber
- Expt 2 -anticipatory activity prior to food closely followed the timing of PAF despite lights coming on 7h before food becoming available (a light-controlled clock would have been out of phase)
- Expt 3 - lack of significant transient activity following LD delay and precise nature of anticipatory feeding activity supports food-entrained clock. Also peak of activity near end of light phase for a few days that then shifted back towards end of PAF suggests food entrained clock