Night Birds

To prolong their days long after sunset, humans developed artificial lighting systems to keep the night illuminated. 

Animals, however, rely on external cues, such as sunlight and temperature, to synchronize their activities with day and night. 

As a result, the light pollution, or artificial light at night (ALAN), is known to disrupt animals’ behavioral and biological rhythms by altering their sleep-wake cycles, namely their circadian rhythms. 

A new study researched how ALAN is affecting the social interactions and behavior of the zebra finch (Taeniopygia guttata), a small bird native to Australia and some Indonesian islands. 

“Social interactions play a significant role in shaping individual and group biological rhythms,” wrote the researchers. “But they are often overlooked in the context of environmental stressors, such as ALAN.” 

Researchers put 104 birds in cages, with about half housed individually and half grouped in sets of six, comprising three females and three males, according to Cosmos Magazine.  

All the birds experienced 12 hours of light and 12 hours of darkness for three weeks.  

After the three weeks had passed, researchers randomly assigned new conditions to the birds. 

Each group was split into two. One social and one isolated group served as controls, while the remaining social and isolated groups were subjected to ALAN for 10 days, experiencing 12 hours of bright light (675 lux), then 12 hours of low-level illumination (around 5 lux), explained Phys.org. 

Lux is the unit of measurement for illuminance, measuring the intensity of light illuminating a surface. 

“We used a light intensity of 5 lux, which is at the higher end of ecologically relevant light exposures,” the researchers wrote. “Using dimmer light intensities will likely result in differences in behavior, gene expression, and physiology.” 

The team monitored the birds’ activity overnight through video cameras and a mechanized perch to record every movement. 

While both the social and isolated groups exposed to night light showed increased activity compared with the groups who spent nights in the dark, the birds that were caged together and exposed to ALAN were more active during the night and became active earlier in the morning. 

The ALAN-exposed birds showed changes in gene expression associated with the circadian rhythm in the hypothalamus (in the brain) and the liver. These changes corresponded with the change in the birds’ activity patterns and were more noticeable in the social group exposed to ALAN. 

“Our investigation into the effects of ALAN on zebra finches reveals that social interactions significantly amplify circadian disruptions,” wrote the authors.