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Role of day length in the regulation of annual testicular cycle in male black-headed munia

Annual changes in day length provide temporal information in the regulation of timing of breeding in birds. In subtropical birds, role of day length in initiation/termination of breeding is well studied in long day breeders, but not in postmonsoon breeders. This study investigated testicular growth in subtropical black-headed munia (Lonchura malacca malacca) exposed to constant day lengths. Groups of male munia were held under long (14 h of light/10 h of dark; 14L: 10D, LD) and short days (10L: 14D, SD) for 16 months. A group held under natural illumination conditions (NDL) served as control. Testicular growth occurred in all photoperiods, although the rate of growth was slower, and hence, testis maturation was delayed under SD. Testis recrudescence–regression cycle occurred under SD, as in NDL control birds, but not in LD in which testis did not regress. It is suggested that day length plays an important role in the regulation of annual testicular cycle in black-headed munia, although with a difference from long day species described thus far. Simultaneous observations of wing primary molt in these groups showed that molt and testicular cycles were unrelated with each other, unlike suggested in other photoperiodic species.