Light Pollution and the Importance of Darkness For Wildlife

Author: Julianne Labreche, Master Gardeners of Ottawa-Carleton

As days become shorter, winter solstice approaches. Long shadows fall over the garden while many migratory birds begin their long, often dangerous, journey south. For gardeners who care about wildlife, autumn is a good time to pause and reflect on the effects of artificial light—especially hazardous for migrating birds and some nocturnal animals too.

Wildlife Refuge

Over time, my own garden has increasingly become a safe refuge for wildlife, including many species of birds. During the coming months, many birds will arrive seeking food, water, and safe passage. In addition to berries, nuts, and seeds, perhaps the best gift that my garden has to offer is a simple one: darkness. It’s easy to remember to switch off the lights.

Importance of Light

The sun is like a clock for animals, naturalists tell us. Changes in light patterns can signal a disruption in the natural cycle of migration and navigation for birds, as well as their cycles of feeding and mating. Cities around the world, including Ottawa, light up the night sky. This creates havoc with these natural cycles. Migratory birds use celestial cues, such as stars, to navigate. Without these cues, they can become confused and disoriented. Tragically, one consequence is that they can die or sustain serious injury by crashing into windows.

Importance of Darkness

Although Ottawa is fortunate to have volunteer organizations like Safe Wings Ottawa that rescue injured birds, as well as the Wild Bird Care Centre that works to rehabilitate them, preventive measures help to avoid injuries. It is much easier to consider the consequences of light pollution and take a few simple actions, such as dimming or turning off the lights. Smart lighting controls and low-intensity lighting options are widely available these days to provide safe options. Some birds are more dependent than others on darkness for their survival. Take the owl that rules the night sky. Its night vision, as well as its acute sense of sound, allow it to find prey—often rodents, including voles and mice.

It is not only birds that benefit from dark nights. This summer, I spent several delightful evenings on the back verandah with lights turned off, watching fireflies. In fact, they are not actually flies at all, but beetles that produce a chemical reaction inside themselves that allows them to light up. Fortunately for fireflies, it is a ‘cold light’ without a lot of energy being lost to heat. Otherwise, they would self-implode in flames. Instead, they are able to fly in search of mates, trying to attract them with their light. When artificial lights are switched on, their dating game is stalled.

For gardeners who live near water, turtles are discouraged from nesting when lights are left on. Hatchlings easily become disoriented as their instinct is to head to the brightest light, following moonlight to water. If they head in the wrong direction, they may perish.

Our night pollinators also are affected by light pollution. It is a common occurrence to see moths drawn to light and then trying to escape it, dying of exhaustion. Many see moths as pests, but some of these insects play a beneficial role in our garden as pollinators. A few Ontario species, such as the luna moth with its lovely sage-green wings, and the giant silk moth, are even as beautiful as butterflies and worth observing some starry nights.

The little brown bat also is a night creature. While not always appreciated, it plays a significant role in eating many ‘bad bugs’, especially mosquitoes, and should be welcomed to our gardens. Light affects bats’ ability to forage, reproduce and communicate with one another. Trees provide many benefits for bats, including places to escape into the darkness.

Finally, perhaps it is not only wildlife that benefits from lights being turned off in the garden. On any night, how wonderful an experience it can be to turn off the lights and gaze at the moon or watch the stars. As we prepare our gardens for another winter and extend the fall harvest by canning, freezing and preserving, sometimes it is good to pause, take a few deep breaths and ponder the night sky and the galaxies beyond.

Tip on Artificial Lighting for Plants

Artificial lighting at night can also affect plants. It can prolong leaf retention in the autumn, affecting winter dormancy. It simulates early bud burst in the spring, making the plant more susceptible to damage during cold weather. Artificial light also reduces a plant’s ability to recover from environmental stresses and causes pollinators and flowers to be out of sync, reducing pollination rates.