Conservation Guardians of Northwest Illinois

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Darkness — Why it Matters

"It's tempting to assume that artificial night light distresses only a few exquisitely sensitive species. But mounting evidence suggests that disappearing darkness undermines our best conservation efforts." So wrote Ben Harder in a 2004 issue of Conservation in Practice, entitled "Degraded Darkness."

Most Conservation Guardians already know of well-publicized effects of artificial night light on Florida's sea turtles: adult females are deterred from coming ashore to hatch their eggs; and new hatchlings perish as they wander inland toward the brighter lights, instead of back out to sea. Only one out of thousands of hatchlings ever reach adulthood. And many of us know well the catastrophic effects of artificial light on birds, most of whom migrate at night. Thrushes, vireos, and warblers, along with many other species, collide with lit towers and buildings during their spring and fall migrations. They also become disoriented and perish from exhaustion when traveling through brightly lit nightscapes. Estimates range upward to 100 million birds killed each year from our artificially lit United States; perhaps 2,500 are killed per year for each lit tower.

Beyond these well-known examples, the science is beginning to point to a universal effect of artificial light at night [ALAN] on people, plants, and animals.

Dr. David Blask of the Bassett Research Institute has been studying the link between cancer and the human hormone melatonin for the last 30 years. At his presentation to the International Dark-Sky meeting in February 2007, he outlined his findings: light at night reduces levels of melatonin, needed for normal sleep cycles and for healthy immunity. Even low levels of light for short periods (less than 2 minutes) dramatically curtail melatonin levels in people. A more amazing finding has been that human breast cancer cells, implanted in mice, grow more rapidly when exposed to ALAN. The higher the light levels, the faster they grow. In natural darkness, the growth rate drops significantly. He stressed the importance to human health of modifying our lighting so as to preserve the night.

At that same meeting, Dr. George Brainard of Jefferson Medical College stated that light is a potent stimulus that regulates our circadian rhythm and human chemistry. He suspects that ALAN will be found to affect every single organism. And he stated that even moths and goldfish have low to no melatonin levels in the daytime, but high levels at night. He believes that light should be considered a therapeutic agent, with the power to heal when used correctly but also the power to do harm when used imprudently.

Dr. Bryant Buchanan, Assistant Professor of Biology at Utica College, told us that all animals regulate cycles of metabolism using the hormone melatonin. He has studied the effects of ALAN on amphibians, and found that tadpoles show 30% slower development when exposed to small increments of artificial light. And the same was true for snails. The more dark at night, the faster the tadpoles and snails grew. Frogs stopped mating activity during night football games.

Travis Longcore, Ph.D., Director of the Urban Wildlands Group, told us that in Germany, 100 billion insects per year are estimated to be killed from artificial light. The calls of green frogs declined by 44% when exposed to intermittent LAN. Robins sing before dawn in lighted cities, exhausting their energy needed for foraging. Beach mice forage less under night lights. Birds prefer naturally light/dark areas for building their nests; the later arrivals are stuck with the areas that lack darkness. Fireflies and glowworms lose their ability to communicate in ALAN. They squander their energy, and reproduction drops off. (Could this be why the populations of fireflies are declining? Notice that one rarely sees fireflies in an artificially lit yard or field.) Dr. Longcore's opinion echoes that of Dr. Buchanan: it increasingly seems that all life contains melatonin that is regulated by cycles of light and dark.

As we have all observed, moths exhibit "flight to light" behavior. The energy a female expends in flying around a light costs her in terms of attracting a mate, and researchers have found that this exhaustion interferes with moths' ability to find prime spots in which to lay their eggs. Many suspect that the decline of moth populations is directly linked to our increasingly 24-hour lit civilization.

While bats seem to flourish around artificial lights, biologists worry that some species are taking over lighted communities and displacing other species of bats. Epidemiologists are concerned that the increased numbers of bats are depleting moths and other insect populations. At least one has reported that after outdoor lights are installed, numbers of circling moths will initially increase and then fall off, suggesting that moth populations are extinguished in that vicinity.

Trees, too, exhibit sensitivity to ALAN. An interesting report in the October 1975 Journal of Arboriculture described some of these effects. "Continuous lighting depresses the formation and maintenance of chlorophyll in leaves and promotes lengthening of the internodes of the branches and expansion of the leaf area. All of these increase the likelihood that the leaves will be more sensitive to air pollution during the growing season."

Some trees have high sensitivity to all-night lighting: maples, birches, elms, sycamores, catalpa, and dogwoods. Sugar maple trees especially are harmed by bright night lighting: next time you encounter a leafy city boulevard of sugar maples, look at the sides next to the street lights to see if they are stunted and browned. After a decade or this kind of stress, the maple trees are more likely to succumb to pests.

There is more research emerging, such as the increase of algae in our lakes brought about by lighted night, the harmful effect on coral, on seabirds, salamanders, and on endangered mammal species. (If interested, consult www.urbanwildlands.org or www.darksky.org.) What has been shown so far is that wildlife, just like people, needs both daylight and darkness to function normally. A deprivation of natural night may produce attraction, repulsion, or disorientation, and this has serious implications for foraging, reproduction, migration, and communication.

One of the most frequent reactions I encounter when talking about light pollution is that everyone is against it—but almost no one believes he or she is responsible for it. It's somebody else's lights that are too bright. But I hope this information points out that every source of artificial light has an effect on the wildlife with which we share our habitat — even those small solar lights placed around the sidewalks and flower beds are harming beneficial insects.

Natural darkness, once abundant, is becoming an endangered resource. But there is good news: researchers are proving the need to conserve it, more people are becoming aware, communities are taking note, lighting regulation is popping up in states and cities, and, best of all, this is one threat can that be repealed. It's the one environmental problem that costs less to solve than to perpetuate.

—Bonnie Garrity