City centre and garden illuminations could prevent the birds dying in harsh winters by helping them feed at night, according to one expert.
Behavioural ecologist Arnaud Da Silva says artificial light, including large city displays and garden fairy lights, may aid birds who cannot build up enough fat during the short winter days to survive the cold nights.
Mr Da Silva has researched the effect of such light on robins – who are particularly sensitive to it – while investigating the effect of light pollution on the timing of songbird singing.
He said: “They’ll probably use the light to forage at night, which could be positive for the bird. It has been shown in cities that robins feed closer to the street lights – an important source of light – during the shortest days.
“There could be benefits in using Christmas illuminations to forage, if the lights are strong enough – particularly in adverse weather and at latitudes where nights are long and cold. UK nights are actually quite long relative to nights in central Europe. I expect the effect to be strongest in Scotland where the nights will be even longer.
“It is a hypothesis – but if they haven’t built up enough fat during the day to survive overnight, they could use the light to keep putting fat on overnight. Birds can lose up to 10 per cent of their weight at night due to heat loss.
“In addition, some robins – especially females – migrate to southern Spain and Portugal, while the rest stay over winter. Therefore the light may help the birds that stayed – the resident robins – to survive over winter. Light may benefit the resident strategy and more birds may stay over winter rather than deciding to migrate.”
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However, Mr Da Silva stressed further research was needed on the drawbacks.
He said: “Birds that suffer sleep deprivation could see costs relating to predation, lifespan and stress, just as night shift workers have been linked with higher prevalence of breast cancer, obesity, depression and other conditions.
“That’s quite clear in humans and there’s no reason to think the negative effects of sleep deprivation may not also apply to birds.”
He added: ‘Work done by my superviser, Bart Kempenaers, showed that in some types that breed very high – at 71 degrees north in Barrow, Alaska – the birds sleeping less were having the most breeding success. This could also be the case with robins.
“There could be some health consequences at the same time as increased reproduction success.”
Mr Da Silva, who is based at the Max Planck Institute for Ornithology in Germany, said: “I’m most interested in dawn singing and the robin is one of the most sensitive species to light and one of the earliest singers in the morning.
“Early singing is a way for the male to guard their territory and a way for him to attract and then guard his mate.”
His latest research found robins on latitudes closer to the Arctic Circle sang for longer, from mid-May, than those on more distant latitudes. Robins in northern Finland sang all night because of the longer days and lighter nights – unlike those in southern Spain and southern Germany, the other areas studied.