Photo-gonadal response of Indian brahminy myna to resonance cycles in different seasons

Abstract

The role of annual changes in day length in regulation of seasonal breeding is widely investigated in a number of subtropical birds. But, how the seasonal changes in bird’s photosensitivity are involved in regulation of breeding in subtropical myna, Sturnus pagodarum, is less understood. We combined the tool of resonance experiments with the seasonal variability in photo-gonadal responses of myna, to investigate whether exposing myna to resonance cycles for 10–12 months starting four different seasons of the year would alter its gonadal recrudescence-regression cycle. Eight groups (n = 5) of myna were transferred to either 6L: 18D (6 h of light/18 h of dark) or 6L: 30D starting March, June, September and December, respectively, and held thence for 10 or 12 months. The observations suggest a seasonal transition between photosensitive, photo-stimulated and photo-insensitive states occurs during different seasons in subtropical myna. The photoperiodic clock involved in the regulation of seasonality in myna appears to follow the principle of external coincidence model, used to explain photoperiodism in many birds.

Keywords:

• Day length
• seasonality
• photosensitive
• resonance cycle
• myna

Acknowledgement

Generous financial support through research grant (F.3-55/2004(SR) dated 14.1.2004) to SKB from the University Grants Commission, New Delhi is gratefully acknowledged. We thank the Principal Chief Conservator of Forests (wildlife), Lucknow for permitting us to work on these small birds