Satellite photos of the Earth at night show glowing cities and urban areas picked out brightly against the darkness. Wherever there are conurbations, artificial light spills out, disrupting the night, disturbing biorhythms and taking an increasing toll on creatures that depend on the darkness to rest and recharge. But no one knew how much of an impact artificial light at night has on birds, which have natural light receptors buried deep in their brains, possibly leaving them more vulnerable than mammals to the disruptive effects of light at night. Dehua Wang, from Shandong University, China, and colleagues from his institution and Wenzhou University, China, collected zebra finches (Taeniopygia guttata) and Bengalese finches (Lonchura striata domestica) from a local breeder and kept some in total nocturnal darkness while others were bathed overnight in streetlight (5 lx) for a month to find out how their metabolism, general health and gut microbiome reacted to the light pollution.
Overall, the Bengalese finches didn't seem too bothered by the night light. Their basal metabolic rate (the metabolism required to keep their basic body functions running) was the same as that of the birds that had had a good night's sleep in complete darkness. Their gut microbiome – which plays a key role in health by supporting metabolism and the production of protective antioxidants – was healthy. And they did not struggle to maintain the proteins in their bodies, although they did gain mass thanks to a larger appetite.
In contrast, the zebra finches appeared to be in bad shape after a month of nocturnal light pollution. Their basal metabolic rate fell as they redirected energy to combat the effects of the nocturnal disruption. They probably had difficulty maintaining their body temperature, because the levels of key proteins involved in body temperature regulation fell. And their gut microbiome was less healthy, with an increase in microbes that cause damaging inflammation and the loss of microbes that contribute to the bird's metabolism and energy supply.
Even though zebra finches and Bengalese finches look superficially similar, their ability to cope with nocturnal light pollution differs remarkably, with zebra finches far more susceptible than the more robust Bengalese finches. And Wang suspects that disruption to the birds’ gut microbiome caused by our addiction to nocturnal light is the key to zebra finch vulnerability.
