Brilliant_ The Evolution of Artificial Light - Jane Brox [114]
But light alone also changes everything. For many nocturnal animals, night is a negotiation between hiding and seeing. Mammals prefer to stay in the shadows and tend to avoid the full moon, which exposes them and makes them vulnerable to predators. Artificial light not only makes it more difficult for animals to hide; it also makes it more difficult for mammals that depend on keen night vision for both food and safety to see:
Many nocturnal species are using only the rod system, and bright lighting saturates their retinas. Although many ... have a rudimentary cone system and can switch over to it within a couple of seconds, during those seconds they are blinded. Once they switch to the cone system, areas illuminated to lower levels become black, and the animal may become disoriented, unable to see the dark area...[ahead] and unwilling to flee into the unseeable shadows whence it came.... Finally, if the animal is in the lighted area long enough to saturate its rod system, it will be at a distinct disadvantage for 10–40 minutes after returning to darkness.
Light also changes the way nocturnal animals negotiate their world. A road lined with streetlights creates a kind of visual barrier: an animal cannot see beyond the lights and must take extra time, caution, and effort to make its way. One scientist, in studying the habits of pumas in southern California, observed that when a puma was "exploring new habitat for the first time, [it] stopped during the night at a lighted highway crossing its direction of travel.... In several instances, the animal would bed down until dawn, selecting a location where it could see the terrain beyond the highway after sunrise. The next evening, the puma would attempt to cross the road if wildland lay beyond or would turn back if industrial land lay beyond."
No less essential for creatures than the dark is the natural light of the night. Since light travels in straight lines, birds and mammals use celestial light for both navigation and orientation. When human light intrudes, it can misinform and confuse them. Consider the consequences of artificial light on birds. For centuries, nocturnal flyers have been drawn to lighthouses. Back when the Eddystone lighthouse keepers were eating their candles, the small light probably wasn't much bother. But a 1912 illustration shows the Eddystone lighthouse clouded by flocks of birds, milling and confused, streaming skyward, circling the white stone tower. In modern times, the dangers are multiplied: birds are drawn to the myriad illuminated windows of tall buildings and skyscrapers, and to the lights on broadcast and communication towers, which they either crash into or circle until they are exhausted. Birds also congregate around the flares on offshore oil and gas plat forms, especially "on misty and foggy nights, and as they fly near and through the flames they are burned to death." And not just elevated lights cause problems: water birds and marsh birds can mistake light-reflecting surfaces for water, and once they land on dry ground, they can't easily take off again. While they struggle to fly away, they remain exposed and vulnerable. And nocturnal seabirds that hunt for bioluminescent prey are mistakenly attracted to lights and confused by them; as a result, their search for food is frustrated. In all cases, if birds that are