Group living is helping crows cope with the harmful effects of light pollution at night in the cities, a study from India has suggested, revealing a previously undocumented benefit of communal roosting in birds.
The study, based on captive crows exposed to nighttime light, is the first to show that group living can help buffer disruptions to the day-night cycle, bolstering evidence for the long-known survival advantages of social living in many species, including humans.
University of Delhi scientists Amaan Buniyaadi and Vinod Kumar have found that while artificial light disturbs sleep in all crows, those kept in groups appear less stressed and cope better with problem-solving tasks than crows kept alone. Their study was published this week in the journal Hormones and Behaviour.
“These findings point to a previously unexplored gain of social living — against artificial light at night,” said Aakansha Sharma, a biological clock expert and an assistant professor at Lucknow University who was not associated with the Delhi study.
Crows are among the most intelligent birds, known for using tools, solving problems and recognising individual humans — capabilities found comparable to those of primates in some studies.
“Social bonding shields the crows from the effects of light pollution — although these results are based on captive crows, they are significant enough for us to ask whether they might apply to other species, including us people,” Sharma told The Telegraph.
Earlier research had shown that social living confers advantages under stress, such as while foraging or defending against predators, but its value under urban conditions like artificial light at night had been largely overlooked.
The Delhi researchers from the university’s zoology department exposed two groups of Indian house crows to natural darkness or dim night light and studied their sleep, hormone levels, emotional behaviour and problem-solving skills.
They found that dim light led to fragmented sleep and disrupted melatonin, the hormone that regulates the sleep-wake cycle. As in earlier studies, the crows exposed to light had lower melatonin than those kept in darkness.
In 2022, Buniyaadi and Kumar had shown that solitary crows under disrupted light cycles display signs of poor mood and lower performance in learning and memory tasks — stress outcomes from fragmented sleep and reduced melatonin.
Now, they have found that crows housed together show fewer signs of stress and perform better. In their study, these birds were more active, groomed and fed more often, and avoided feather-plucking — a stress-linked behaviour — unlike solitary birds.
They also had a greater ability to take on new problem-solving tasks. This was linked to changes in brain gene activity associated with emotion, motivation and decision-making.
University of Delhi scientists Amaan Buniyaadi and Vinod Kumar. Sourced by The Telegraph
"We’ve long known that social animals help each other survive in stressful conditions, avoid predators and find food — this study adds city lights to that list," said Buniyaadi.
"Social bonds seem to soften the emotional and behavioural toll of living under artificial light, even if they don’t fix the disrupted biology completely."
The researchers observed that social living did not offset all effects of artificial light. Melatonin remained low, and sleep stayed disturbed in the group-housed crows.
The findings echo earlier studies in chicks, mice and pigs where group-housed animals showed better mood and behaviour.
Independent studies in people have found links between sleep disorders and psychiatric illness. A 2018 study of over 91,000 people published in The Lancet Psychiatry found that disrupted body clock rhythms increase the risk of depression and bipolar disorder.
"The idea that social environments could help offset some mental health effects of poor sleep isn’t new in humans," Sharma said. "What’s striking here is how clearly that idea shows up in birds — it comes as a fresh reminder of our shared biology."