Impact of Light at Night Is Phase Dependent: A Study on Migratory Redheaded Bunting (Emberiza bruniceps)

Abstract

Artificial light at night (LAN) alters the physiology and behavior of an organism; however, very little is known about phase-dependent effects of LAN, particularly, in night migratory songbirds. Therefore, in this study, we investigated whether the effects of LAN on daily activity and photoperiodic responses in the Palearctic Indian migratory songbird, redheaded buntings (Emberiza bruniceps), is dependent on the different phases of the night. Male buntings maintained under short photoperiod (8L:16D; L = 100 lux, D < 0.1 lux) in individual activity cages were exposed to LAN (2 lux) for 6 weeks either in 4 h bin given at the different phases of 16 h night (early, mid, or late at ZT 08–12, ZT 14–18, or ZT 20–24, respectively; n = 9 each group) or throughout 16 h night (all night light, n = 6, ZT 08–24, the time of lights ON was considered as Zeitgeber time 0, ZT 0). A group (n = 6) with no LAN served as control. The results showed that LAN at the different phases of night induced differential effects as shown by an intense activity during the night, altered melatonin and temperature rhythms, and showed an increase in body mass and body fattening, food intake, and gonadal size. Midnight light exposure has a greater impact on migration and reproduction linked phenotypes, which is similar to the ones that received light throughout the night. The highlights of this study are that (i) LAN impacts day-night activity behavior, (ii) its continuity with the day alters the perception of day length, (iii) birds showed differential sensitivity to LAN in a phase-dependent manner, (iv) the direction of placing LAN affects the daily responses, e.g., LAN in the early night was “accepted” as extended dusk but the late night was considered as early dawn, and (v) midnight LAN was most effective and induced similar responses as continuous LAN. Overall, LAN induces long day responses in short days and shows differential sensitivity of the different phases of the night toward the light. This information may be valuable in adopting a part-night lighting approach to help reduce the physiological burden, such as early migration and reproduction, of artificial lighting on the nocturnal migrants.

Species sensitivities to artificial light at night: A phylogenetically controlled multilevel meta‐analysis on melatonin suppression

“…The phase‐dependent response of melatonin secretion provides valuable insights into the underlying mechanisms of how ALAN affects cues for the timings of biological processes (Bedrosian & Nelson, 2017; Gaston et al., 2017), where the early night may be perceived as an extension of ‘subjective’ dusk and late‐night as ‘subjective’ early dawn. This interpretation is supported by the behavioural changes observed in buntings ( Emberiza bruniceps ), which extend their daytime activity into the early night and advance the onset of daytime activity into the late night when exposed to ALAN (Kumar et al., 2021).…”

“…First, we can tune the spectral composition of artificial light sources used at night to minimize the proportion of blue light (Gaston & Sánchez de Miguel, 2022), because our meta‐analytic finding confirmed that short wavelengths (blue portion) suppress melatonin levels more than other wavelengths across species. Second, we can adopt a discontinuous lighting strategy (Kumar et al., 2021), such as using motion sensors to turn lights on or higher only when necessary and avoiding artificial lighting during midnight hours. Third, we should reduce the light intensity of all types of artificial light to mitigate the impact on melatonin suppression (Agathokleous, 2023).…”

Endocrine–circadian interactions in birds: implications when nights are no longer dark

“…5–5.0 lux) in great tits [133], European blackbirds [66] and zebra finch [134]. Importantly, as expected for a circadian mechanism, the melatonin response to part-time ALAN was phase-specific, as shown in a study of migratory red-headed buntings ( Emberiza bruniceps ) [135].…”

Photoperiodic regulation of avian physiology: From external coincidence to seasonal reproduction

“…The annual change in daylength is the predominant predictive cue that birds used to time seasonal rhythms (Dawson, 2001; Tolla & Stevenson, 2020). Of all the avian models currently in use for the study of photoperiod and reproductive development, few are more studied than Japanese quail ( Coturnix japonica ) and migratory buntings (Huss et al, 2008; J. Kumar et al, 2021). Japanese quail show incredibly robust changes in reproductive physiology and in their neuroendocrine response to increased photoperiod (Stevenson et al, 2022).…”

“…development, few are more studied than Japanese quail (Coturnix japonica) and migratory buntings (Huss et al, 2008;J. Kumar et al, 2021).…”