Evrim Yazgin
Cosmos science journalist
Light pollution is a growing concern for the wellbeing of different animal species. Now researchers have found that artificial light is negatively impacting the brains of social birds.
The study, published in the Proceedings of the Royal Society B, focused on the zebra finch (Taeniopygia guttata) – a small bird found across Australia and islands of Indonesia.
Zebra finches are a “model organism” widely used in studies in various scientific fields.
Artificial light at night (ALAN) is an increasingly common disruptor of the natural physiological and behavioural rhythms of many animals. The researchers of the new study note: “Social interactions play a significant role in shaping individual and group biological rhythms, but they are often overlooked in the context of environmental stressors, such as ALAN.”
So they sought to understand how the social interactions in zebra finches were interrupted by ALAN and how this in turn affected the birds’ behaviour.
The team placed 104 birds in cages and subjected them to 12 hours of light followed by 12 hours of darkness for 3 weeks. Roughly half of the birds were in cages by themselves, while the rest of the birds were in groups of 6 made up of 3 males and 3 females.
While 5 of the birds died toward the end of the experiment, including 2 in one grouped cage, the researchers noted that this did not have noticeable impacts on the social interactions of the remaining birds.
Following the 3 weeks of alternating light and darkness every 12 hours, the birds were randomly assigned new conditions.
About half of the isolated birds were subjected to conditions mimicking ALAN – 12 hours of light (675 lux) followed by 12 hours of dimmed light (about 5 lux). The other half continued with 12 hours of light and 12 hours of darkness. The same conditions were prepared for the grouped birds. These new conditions – half of the birds with ALAN and half without – continued for 10 days and the birds were monitored throughout.
Unsurprisingly, birds exposed to ALAN were significantly more active at night, affecting expression of genes associated with the regulation of circadian rhythms (sleep/awake cycles).
Birds in the grouped cages exposed to ALAN started their daily activities earlier and had more disrupted natural rhythms in their brain and livers compared to the isolated birds who were also exposed to ALAN.
“Our investigation into the effects of ALAN on zebra finches reveals that social interactions significantly amplify circadian disruptions,” the authors write.
“These changes occurred over a relatively short period of 10 days. Future research should investigate the long-term effects of social conditions, as other research has demonstrated persistent as well as habituated effects of long-term ALAN. For example, there may be social buffering or habituation effects with longer exposures,” they add.