Artificial light at night advances avian reproductive physiology

Abstract

Artificial light at night is a rapidly increasing phenomenon and it is presumed to have global implications. Light at night has been associated with health problems in humans as a consequence of altered biological rhythms. Effects on wild animals have been less investigated, but light at night has often been assumed to affect seasonal cycles of urban dwellers. Using light loggers attached to free-living European blackbirds (Turdus merula), we first measured light intensity at night which forest and city birds are subjected to in the wild. Then we used these measurements to test for the effect of light at night on timing of reproductive physiology. Captive city and forest blackbirds were exposed to either dark nights or very low light intensities at night (0.3 lux). Birds exposed to light at night developed their reproductive system up to one month earlier, and also moulted earlier, than birds kept under dark nights. Furthermore, city birds responded differently than forest individuals to the light at night treatment, suggesting that urbanization can alter the physiological phenotype of songbirds. Our results emphasize the impact of human-induced lighting on the ecology of millions of animals living in cities and call for an understanding of the fitness consequences of light pollution.

Habitat type, food resources, noise and light pollution explain the species composition, abundance and stability of a winter bird assemblage in an urban environment

“…However, light at night is considered as a major driver of change in timing of daily activity. Light pollution effect has been studied mainly during the breeding period and in the context of extended vocal activity associated with displaying behaviour (Miller 2006;Da Silva et al 2015) and earlier development of reproductive system (Kempenaers et al 2010;Dominoni et al 2013). In contrast, the effect of artificial lights on the timing of behaviours during winter has received relatively little attention.…”

Chronobiology by moonlight

“…In addition, female provisioning rate to the chicks during the second part of the nestling phase was increased in great tits (Parus major), suggesting that there might be fitness consequences due to the high workload [148]. Furthermore, besides affecting daily cycles, light pollution has been found to advance the growth of the reproductive system in European blackbirds (Turdus merula) [149] and the time of egg laying in the blue tit (Cyanistes caeruleus) [147] and has therefore been hypothesized to be one of the driving factors responsible for the earlier onset of reproduction in birds thriving in urban areas [150,151].…”

Melatonin: a possible link between the presence of artificial light at night and reductions in biological fitness

“…Human studies are typically correlational, but similar carcinogenic and immunosuppressant effects of artificial night lighting have been observed from laboratory experiments on mice and rats [23][24][25][26], although immune-enhancing effects of dim night lighting have also been reported [27]. Convincing support for the link between LAN and significant modifications to both behaviour (activity patterns) and physiology (moult dates and reproductive status) also comes from a series of long-term studies combining field and experimental trials on European blackbirds (Turdus merula) [12,18,28,29]. However, despite the recent surge in research on the impacts of night lighting within the fields of ecology and medicine, we still lack broad-scale, cross-species experimental evidence of the negative effects of LAN (but see [30]).…”

“…Behaviourally, LAN is linked to an increase in the observed number of bird strikes and subsequent deaths [6,7] and changes in the foraging capacity and activity patterns of vertebrates [8][9][10][11][12] and invertebrates [5,13]. At the population level, animals living in well-lit urban environments are observed to shift the timing and structure of their mating calls [14][15][16][17] and the commencement of breeding [15,18]. Evidence documenting the physiological impact of LAN comes largely from correlational studies of vertebrate (often human) health.…”