Abstract
Circadian rhythms are more synchronized in birds than mammals. Circadian clock functions as a timing reference allow organisms fluctuations in their environments and are the basis for the transduction of seasonality from photoperiod. The present study was performed to determine the effect of constant dim and bright light illumination on circadian behavior of baya weaver bird (Ploceus philippinus), black-headed munia (Lonchura malaca malaca), and red-headed bunting (Emberiza bruniceps). It analyzed the data of locomotors activity of these under the effect of different photoperiods (12L: 12D and 8L: 16D) for a period of 30 days. In the captivity, birds were acclimatized for 4 weeks and were subjected to photoperiodic chambers (60×45×35 cm3) providing short-day conditions (8h light: 16h darkness; 8L:16D). Total activity profile was observed for 30 days under 12L: 12D and 8L: 16D photoperiod. Under 12 L: 12D photoperiod, significant response was observed in two of the four birds in daily profile of baya weaver bird and also in black-headed munia but the marginal significant response noticed in one of the four birds under 8L: 16D. The comparison of day and night total activity count in baya weaver bird and black-headed munia showed the maximum activity in weaver bird under 12L: 12D photoperiod.
Introduction
Organisms maximize their fitness by synchronizing their physiology and behavior with the abiotic and biotic features of their environments. This can be possible by endogenous circadian clocks, when they prevailing with light, food, and socio environments, determine temporal patterns of events during the day in daily functions as activity–rest, sleep–wake, and feeding patterns. At the regulatory level, circadian clocks govern changes in physiology and behavior within each day; hence, behavioral and physiological functions exhibit daily and circadian rhythms under periodic daily light–dark (LD) cycles and constant dim light or darkness, respectively. 1 Organisms synchronize their behavioral activities under natural conditions but under artificial laboratory conditions, their activity mainly synchronized with the alternation of day and night, with the two phases of different light intensities. 2 Circadian rhythm is fragile for daily behavioral patterns and advanced brain functions such as learning and cognition in animals. 3
Especially in birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep–wake, visual function, song, migratory patterns, and orientation, as well as seasonal patterns of reproduction, song, and migration. Like other organisms, birds also need to adapt their physiology and behavior to the regular cycles (daily, tidal, and annual) in their environment. Nocturnal birds active during the night and quiet during the day. Diurnal birds do vice-versa. During the year, birds need to control the time and duration of the different life history stages that make up the annual cycle in some species: reproduction, molt, vernal migration, and autumnal migration. 4 Circadian rhythms are oscillations in the certain activities of organisms with a period close to 24 h. 5 Circadian rhythms have some basic characteristics. First, the rhythm is an innate property of the organism and is maintained under constant natural and artificial conditions. Second, the period length is temperature compensated, so that it is maintained at a constant rate throughout the physiological range of external temperature. Third, circadian rhythms are fully synchronized with the outside world by light. These rhythmic characteristics of the organisms to maintain own rhythm for these predictable environment changes. In the temperate latitudes, the photoperiodic cycle (LD) within a 24-hour period synchronizes diurnal rhythmicity in many species. 1 Although the temperature and other environmental factors can synchronize the rhythm with the environment under certain conditions, light is the predominant and perhaps the only physiologically relevant environmental cue (or zeitgeber from German zeit = time and geber = giver) for synchronizing the circadian rhythm with the light–dark cycle. We aimed to find circadian activity of passerine finches in captivity in different photoperiod. For this study, we will take three model species which are “photosensitive” in nature.
Methodology
Study species
The locomotors activity data analysis was performed on three different, highly photosensitive in which, Indian weaver bird (Ploceus philippinus) is a non-migratory species, locally distributed, sparrow-sized ploceid and it measures 15 cm in length and is sexually dimorphic species, that is, males and females are easily distinguished during breeding season. Black-headed munia (Lonchura malacca Malacca) is a winter migrating, small gregarious bird and its length is 11–12 cm. This is a medium-sized munia with a black head and chest nut body, contrasting. Red-headed bunting (Emberiza bruniceps) is a passerine finch, and it breeds in central Asia. It is winter migratory in India. It is 17 cm long and has long tail. It is beautiful with golden brown head and under par yellow, but female is dull looking ashy brown head, buffish washed with yellow (below) and under tail-coverts yellow.
Procurement and maintenance
Data analysis was performed on three species, highly photosensitive, that is, Indian weaver bird, black-headed munia, and red-headed bunting. All experiments were performed in captivity. Indian weaver birds were kept in group I (n = 4), black-headed munia were kept in group II (n = 4), and black-headed munia were kept in Group III (n = 4). These birds were acclimatized for 4 weeks and were subjected to artificial photoperiodic chambers (60×45×35 cm3) at different photoperiod. In which two groups of them (black-headed munia and Indian weaver bird) providing short-day conditions (8 h light: 16 h darkness; 8L: 16D) and (under 12 h L light: 12 h darkness; 12 L: 12 D). Food and water were provided ad libitum. Food mainly consisted of seeds of Setaria italic and Oryza sativa.
Lighting condition
Fluorescent tubes or CFL lamps (14-watt cool compact fluorescent lamp; model B22 BC from Philips India Ltd.) were used for providing during artificial lightening condition. The spectral range of light is between 400 and 700 nm and intensity is 250 lux. Temperature is about 30–35°C. The ON and OFF activity of light was regulated by automatic time switches (Müller clock, Germany). Light intensity was measured by the radiometer (model no. Q203 from Macam Photometrics Ltd., Scotland).
Light regime
In this experiment, total of 12 individuals were taken for the locomotors data analysis. Group I and group II were kept individually under 12L: 12D, and group III was under 8L: 16D photoperiodic regime for 1 month (30 days). Locomotors activity recorded continuously at 30 days. Food and water were provided ad libitum during entire period of experiment. 50 gm pearl millets and 2–3 boiled egg provided within 2–3 days per 4 individual. Water changed as same.
Locomotors activity recording and analysis
The locomotors activity was considered as a reliable assay for study of circadian property and it was measured easily under captive condition. 6 The Chronobiology Kit software from Stanford Software Systems, Stanford, California, USA, was used to recording and analysis of the locomotors activity of bird. 6 The recording of locomotors activity (actogram) was double-plotted. Circadian period and activity profile (daily and day/night profile) were observed for 30 days under 12L: 12D and 8L: 16D photoperiod. Activity count was analyzed by Kit-analyze program. We measured the locomotors activity strength by The ACTCNT program of The Chronobiology Kit. For this, the counts recorded at during the specified period of 24 h (daily profile), 12 h/12 h (day/night), and 8 h/ 16 h (day/night) (0–12 or hour 12–24; hour 0 = time of the light on at the beginning) for 30 days for each bird, and then the mean (±SE) for the group was calculated.
Statistical analysis
The statistical tools applied in this work included the mean, standard error, and one-way RM ANOVA with and without Newman–Keuls post hoc tests. Significance was taken at p < 0.05. Statistical analysis was carried out using graph pad prism software (version 3.0 La Jolla, CA, USA).
Result
Data analysis showed that daily profile of weaver bird, black-headed munia, and red-headed bunting exposed fewer than 12L: 12D and 8L: 16D photoperiod. Under 12 L: 12D, birds followed the LD cycle and were active during light period and no activity bouts were present during night time. Except for individual variations, the general trend of activity was similar in all the birds. All birds are diurnal species and its activity was restricted during the daytime. In general, the activity onsets and offset followed to the timing of light onset and offset. It also revealed by daily and day–night profile graph (Figure 1). All birds showed rhythmicity under LD phase. In LD condition, all birds of both the groups were active during the daytime period (L) under 12L and 8L photoperiod during data observation period. Locomotors activity of all birds was concise during light phase but the weaver birds were more active and activity bouts were present in condensed manner in comparison with black-headed munia and red-headed bunting. In 8 h light period, activity movement of red-headed bunting was confined only during light period and birds were active only during the daytime. Daily profile of Indian weaver bird under 12L: 12D photoperiod significant response was observed in two of the four birds; RKPNI 12 and 15 (F3, 69 = 16.54, p < 0.0001; one-way RM ANOVA) (Figure 1(a)). In black-headed munia under 12L: 12D Photoperiod significant response was observed in two of the four birds; RKPNI 14 and 16 (F3, 69 = 17.98, p < 0.0001; one-way RM ANOVA) (Figure 1(b)). But the marginal significant response noticed in one of the four birds under 8L: 16D (F3, 69 = 3.865, p = 0.0130; one-way RM ANOVA) (Figure 1(c)). The comparison of day and night total activity count in baya weaver and black-headed munia showed the maximum activity in weaver bird under 12L: 12D photoperiod (Figure 2). The minimum activity was noticed in red-headed bunting under 8L: 16D photoperiod during the daytime activity count (Figure 2). But, there is no significant difference in day and nighttime activity count between weaver bird, black-headed munia, and red-headed bunting (p = 0.1138; student unpaired t-test) (Figure 2). Daily profileandday/night count (valuesaremeans ± SEM) have been shown in figures a, b, and c (dailyprofile) and figures d, e, and f (day/night activity count) under 12L:12D and 8L:16D in weaver bird, black-headed munia, and red-head edbunting for a period of 30 days. (*=RKPNI15; one-way repeated measures analysis of variance; Newman–Keuls post hoc test). Day/night activity count (values are means ± SE) under 12L:12D and 8L:16D in weaver bird, black-headed munia, and red-headed bunting for a period of 30 days.
Discussion
In this experiment, we analyzed the data of circadian rhythm of weaver bird, black-headed munia, and red-headed bunting birds under different light regimes: 12L: 12D and 8L: 16D photoperiod. We found that birds were active during the daytime, and locomotors activity was completely absent during the nighttime. The circadian periodicity was seen in all birds under 12L: 12D and 8L: 16D in all birds in all species. Similarly, modifications of the expression of the behavioral rhythm under different light were observed in some species of Japanese quail.
7
In general, avian circadian and photoperiodic responses depend on the subjective interpretation of day and night illumination; hence, the photo phase contrast rather than on the day light intensity alone as has been studied in different birds such as Japanese quail, Coturnix c. japonica
2
; black-headed bunting, Emberiza melanocephala
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; and Indian weaver bird, Ploceus philippinus.
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The effect of light wavelength on seasonal reproductive phenomenon has been well documented in migratory black-headed buntings (Emberiza melanocephala). After analysis of data, we observed in that the daily and total activity count was high in Indian weaver bird and low in red-headed night migratory bunting species. So, some physiological and behavioral character varies from bird species to species when bird housed individually in locomotor activity cages. These data analyses are further required to be performed to validate this phenomenon. The present study was performed to determine the effect of constant dim and bright light illumination on circadian behavior of Indian weaver bird, Ploceus philippinus. The effects of constant dim and bright light on the expression of the circadian rhythm were investigated in these experiments. Few earliest finding suggest that the circadian behavior of Indian weaver bird is regulated by the light intensity and other environmental factors.
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All birds are diurnal species and its activity was restricted during the daytime (Figure 3; left panel). In general, the activity onsets and offset followed to the timing of light onset and offset. It also revealed by daily and day–night profile graphs (Figure 1). All birds showed rhythmicity under LD phase. In LD condition, all birds of both the groups were active during the daytime period (L) under 12L and 8L photoperiod during experimental period. In 8-h light period, activity movement of red-headed bunting was confined only during light period and birds were active only during the daytime (Figure 3). After analysis of data, we observed that the daily and total activity count was high in Indian weaver bird and low in red-headed night migratory bunting species. So, some physiological and behavioral character varies from bird species to species when bird housed individually in locomotor activity cages. These data analyses are further required to be performed to validate this phenomenon. Showing locomotor activity recording with associated instruments.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
