“San Francisco at night. (Photo: Niyantha Shekar)

“San Francisco – High on bluffs overlooking the Pacific, Dominik Mosur was strolling along at 2 a.m. searching for owls. Darkness enveloped the Presidio, a historic military encampment turned national park, as Mosur made his way through cypress-scented fog.

“Alert in the mist as he cut through a forest, Mosur listened for the hoot of the great horned owl. Instead, he heard the singing of a bird that should have been asleep in its nest until dawn. The Nuttall’s white crowned sparrow was throbbing away with its distinctive zu-zee trill.

“To this day, Mosur wonders whether the bright street lamps, 50 feet from the songbird’s territory, caused its odd nocturnal behavior, which usually is limited to moonlit nights along this part of the coast.

“Mosur puzzled over the toll that the nighttime singing was taking on the songbird: Would it have the energy in the morning to defend its territory, attract a mate and raise its young?

“Around the world, scientists seeking to answer that question have gathered mounting evidence that city lights are altering the basic physiology of urban birds, suppressing their estrogen and testosterone and changing their singing, mating and feeding behaviors. One lab experiment showed that male blackbirds did not develop reproductive organs during the second year of exposure to continuous light at night.

“Streetlights, shopping centers, stadiums and houses turn night into day, a phenomenon that scientists call “loss of night.”

“Birds are particularly sensitive to light and different chemical interventions. If you see these deleterious effects in the birds, you’re likely to see them in humans in short-order. The smart thing to do is to pay attention to avian life,” said Vincent Cassone, whose University of Kentucky lab examines neuroendocrine systems of birds and mammals.

“People can suffer an array of health problems when they work night shifts that alter their circadian, or daily, cycles governed by a biological clock. In the wild, light pollution causes hatchling sea turtles to lose their way from beach to the ocean, and disorients Monarch butterflies searching for migration routes. In field experiments, Atlantic salmon swim at odd times, and frogs stop mating under skies glowing from stadium lights at football games. Millions of birds die from collisions with brightly lit communication towers, and migratory flocks are confused by signals gone awry.

“More recently, researchers have documented an earlier dawn chorus, which influences mate selection, feeding and interplay among species. At a deeper, molecular level, the changes in birds’ hormones raise questions about their reproductive fitness and the potential for ecological and evolutionary consequences.

“Western scrub-jays were used in an experiment that showed sex hormones were altered by artificial light at night. (Photo: Francesco Veronesi)

“Under light at night, something gets broken and you see a dampening of their hormonal system,” said University of Memphis biology professor Stephan Schoech, who found hormone changes in western scrub-jays.”