Biochronometry of photoperiodically induced fat deposition in a migratory finch, the Blackheaded bunting (Emberiza melanocephala) (Aves)

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Abstract
This investigation attempts to identify the mechanism(s) involved in the fat deposition in a photoperiodic migratory species, the Blackheaded bunting (Emberiza melanocephala). Groups of photosensitive male buntings were exposed to resonance, interrupted night, and ultra‐short‐day light cycles for 35, 42 and 75 days, respectively. Birds were weighed at the beginning and at the end of the experiments. Those exposed to ultra‐short‐day light cycles were also weighed at critical intervals during the treatment period. Our results indicate that: (a) a light‐sensitive rhythm with a period of about 24 hr is involved in the photoperiodic induction of premigratory fattening and weight gain in Blackheaded buntings: (b) buntings possess a bimodal pattern 'of sensitivity to photoperiods that induce fattening, and (c) this endogenous circadian rhythm can be entrained by an ultrashort photophase of 3 h if the latter is coupled with scotophases of specific duration.