If you've noticed that you're hearing birdsong longer into your day than you used to, your observation fits with those made by researchers examining millions of hours of tweets and warbles. But just why are our feathered friends holding longer concerts?
The reason, the authors of a new study postulate, has to do with light pollution.
To reach their conclusion, researchers from Southern Illinois University and Oklahoma State University analyzed 2.6 million onsets of birdsong in the morning and cessations of it in the evening. The data they used came from the BirdWeather project, a citizen scientist effort in which bird enthusiasts mount bioacoustic devices in their yards to capture environmental sounds. Built-in software separates out bird song from other sounds and that information is fed back to the project, which offers a real-time map of bird locations and other data.
As part of its new analysis, the team studied the patterns of 583 diurnal species. The researchers found that birds in areas containing the most man-made light pollution are singing 50 minutes longer than those not exposed to extra light. Specifically, the birds in the brightest landscapes began singing about 18 minutes sooner than those in the darkest areas, and they continue for 32 minutes later into the night.
The researchers say that the birds most affected were those species with large eyes, open nests, and large ranges. The effects of light pollution on singing patterns was also most notable during breeding seasons. The team says that it's unclear if the impact to singing is positive, negative or neutral in terms of the health of the birds.
"On the one hand, 50 minutes of prolonged activity may represent a substantial loss of resting time, particularly during the breeding season, which is an already demanding period for birds," the scientists write in their study, which has been published in the journal Science. "However, prolonged activity may not translate to sleep debt and the detrimental effects thereof if birds can rest during the day, sleep more intensely during periods of nonactivity, or sleep with one brain hemisphere during activity. Indeed, light pollution–related changes to activity may lead to positive fitness effects if they facilitate increased foraging time or reproductive output."
It's now estimated that 80% of life on Earth lives beneath light polluted skies – areas where man-made light pushes back the natural darkness the planet would otherwise experience at night. Known as "skyglow," the phenomenon has caused the death of insects that collide with lights; disruption to the patterns of nocturnally migrating birds; the altering of seasonal hormonal rhythms; and problems with reproductive habits such as with sea turtles that get disoriented by artificial light when they come ashore to lay their eggs and hatchlings that lose their way after birth.
The researchers say that their findings are key to understanding how excess artificial light is affecting birds but believe more investigation – and perhaps governmental action – is needed.
"Further accumulation of global data may also motivate development of intergovernmental policy – akin to climate change efforts – to counteract light pollution," they conclude. "Restoring the darkness of our nights is a preeminent challenge for 21st-century conservation and demands global cooperation."
Source: American Association for the Advancement of Science via EurekAlert
