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Arnaud Da Silva, J. M. S., Emmi Schlicht, Mihai Valcu, Bart Kempenaers. (2014). Artificial night lighting rather than traffic noise affects the daily timing of dawn and dusk singing in common European songbirds. Behavioral Ecology, 25(5), 1037–1047.
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Brüning A., H., F., Franke, S., Preuer, T., Kloas, W. (2015). Spotlight on fish: Light pollution affects circadian rhythms of European perch but does not cause stress. Sci Total Environ, 511, 516–522.
Abstract: Flora and fauna evolved under natural day and night cycles. However, natural light is now enhanced by artificial light at night, particularly in urban areas. This alteration of natural light environments during the night is hypothesised to alter biological rhythms in fish, by effecting night-time production of the hormone melatonin. Artificial light at night is also expected to increase the stress level of fish, resulting in higher cortisol production. In laboratory experiments, European perch (Perca fluviatilis) were exposed to four different light intensities during the night, 0 lx (control), 1 lx (potential light level in urban waters), 10 lx (typical street lighting at night) and 100 lx. Melatonin and cortisol concentrations were measured from water samples every 3 h during a 24 hour period. This study revealed that the nocturnal increase in melatonin production was inhibited even at the lowest light level of 1 lx. However, cortisol levels did not differ between control and treatment illumination levels. We conclude that artificial light at night at very low intensities may disturb biological rhythms in fish since nocturnal light levels around 1 lx are already found in urban waters. However, enhanced stress induction could not be demonstrated.
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Da Silva, A., de Jong, M., van Grunsven, R., H A Visser, M., E Kempenaers, B., & Spoelstra, K. (2017). Experimental illumination of a forest: no effects of lights of different colours on the onset of the dawn chorus in songbirds. Royal Society Open Science, 4(1), 160638.
Abstract: Light pollution is increasing exponentially, but its impact on animal behaviour is still poorly understood. For songbirds, the most repeatable finding is that artificial night lighting leads to an earlier daily onset of dawn singing. Most of these studies are, however, correlational and cannot entirely dissociate effects of light pollution from other effects of urbanization. In addition, there are no studies in which the effects of different light colours on singing have been tested. Here, we investigated whether the timing of dawn singing in wild songbirds is influenced by artificial light using an experimental set-up with conventional street lights. We illuminated eight previously dark forest edges with white, green, red or no light, and recorded daily onset of dawn singing during the breeding season. Based on earlier work, we predicted that onset of singing would be earlier in the lighted treatments, with the strongest effects in the early-singing species. However, we found no significant effect of the experimental night lighting (of any colour) in the 14 species for which we obtained sufficient data. Confounding effects of urbanization in previous studies may explain these results, but we also suggest that the experimental night lighting may not have been strong enough to have an effect on singing.
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de Jong, M., Jeninga, L., Ouyang, J. Q., van Oers, K., Spoelstra, K., & Visser, M. E. (2015). Dose-dependent responses of avian daily rhythms to artificial light at night. Physiol Behav, 155, 172–179.
Abstract: Recent studies have shown that animals are affected by night-time light exposure. Light is a continuous variable, but our knowledge on how individuals react to different light intensities during the night is limited. We therefore determined the relationship between night light intensity and the behaviour and physiology of great tits (Parus major). We measured daily activity patterns and melatonin levels in 35 males exposed to five different light intensities and found strong, dose-dependent effects. Activity onset was increasingly advanced, and activity offset delayed with higher light intensities. Furthermore, night-time activity increased and melatonin levels measured at midnight decreased with higher intensities. In this experimental study, we demonstrate for the first time dose-dependent effects of artificial light at night on birds' daily activity patterns and melatonin levels. Our results imply that these effects are not limited to a certain threshold, but emerge even when nocturnal light levels are slightly increased. However, in a natural area, these effects may be limited as artificial light levels are commonly low; light intensities drop rapidly with distance from a light source and birds can avoid exposure to light at night. Future studies should thus focus on examining the impact of different intensities of light at night in the wild.
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Deveson, S. L., Arendt, J., & Forsyth, I. A. (1990). Sensitivity of Goats to a Light Pulse During the Night as Assessed by Suppression of Melatonin Concentrations in the Plasma. Journal of Pineal Research, 8(2), 169–177.
Abstract: This study investigates the ability of a 1 h light pulse of different intensities at night to suppress plasma melatonin in goats. Six female Saanen dairy goats, about 2 yr old, were housed in a light-tight shed. The goats were habituated for 1 wk to an 8L: 16D photoperiod (40.70 ± 4.16 μW/cm2; 137 ± 14 lux), lights on 0800 h. A 1 h light pulse, of different intensity on each occasion, was given from 1900 to 2000 h. Light intensity was measured by using a lux meter (mean of 36 measurements at goat's eye level). Five different light intensities were given during December in the order 4.22 ± 0.62 μW/cm2 (14.2 ± 2.1 lux), 0.68 ± 0.09 μW/cm2 (2.3 ± 0.3 lux), 0.26 ± 0.004 μW/cm2 (O.87 ± 0.14 lux), darkness, 40.70 ± 4.16 μW/cm2 (137 ± 14 lux), with 1–3 d between treatments. The goats were bled hourly from 1500 to 1900 h and every 15 min from 1900 to 2100 h, and a last bleed occurred at 2200 h. Dark-phase samples were taken in dim red light (<0.03 μW/cm2; 0.1 lux). Plasma was assayed for melatonin by radioimmunoassay. Suppression of melatonin concentrations increased as light intensity increased as follows: Darkness, 0%; 0.26 ± 0.004 μW/cm2; 0%; 0.68 ± 0.09 μW/cm2; 43.1%; 4.22 ± 0.62 μW/cm2, 71.1%; 40.70 ± 4.16 μW/cm2, 81.2%. Suppression was significant (P<0.05) at light intensities >0.68 μW/cm2, 2.3 lux. A hyperbolic relationship existed between percent suppression and light intensities.
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