Effect of Photoperiod and Illuminance on Daily Activity Patterns, Physiology, and NPY Peptide Expression in Migratory Redheaded Buntings (Emberiza bruniceps)

Abstract

Introduction Light is the primary source of energy and regulates seasonal changes in physiology and behavior. The role of photoperiod has been much investigated in several bird species, but the role of illumination in seasonal adaptations of passerine finches is less understood. We, therefore, investigated the effects of photoperiod and illuminance on migratory physiology in a Palearctic-Indian migratory finch, redheaded bunting (Emberiza bruncieps). Methods Photosensitive buntings maintained under short days (8L:16D) were divided into three groups receiving 5, 25, and 100 lux of white daytime illuminance respectively. Thereafter, using photoperiodic manipulation three life history states, i.e., nonmigratory (NM), premigratory (PM), and migratory (MIG) states were induced in the buntings. The birds in the MIG state were consecutively perfused after seven nights of Zugunruhe (nighttime migratory restlessness) for NPY-immunohistochemistry, which is involved in a wide range of functions including energy homeostasis, vision, and fat deposition in birds. Results We found differential effects of illuminance on locomotor activity and physiology. Photostimulated birds showed intense nighttime activity in the MIG state. We observed premigratory hyperphagia in the birds, with increased food intake in the 100 lux group, which was reflected in the body mass gain in the MIG state. NPY neuropeptide expression on the periphery of the n. rotundus (pROT), suggests its potential role in visual acuity, where the NPY-cell count significantly decreased under 25 lux illumination. Conclusion We demonstrate that migrating birds may also experience physiological effects from changes in daytime illumination. We observed illuminance-dependent variations in the quantity of food consumed by the birds. It indicates that the illuminance may also impact the encephalic centers that control food intake.