Ian Stewart, Ornithologist, and Robin Glazer, Environmental Advocate
Just as the excitement is mounting for our upcoming spring Native Plant Sale, the number of migrating birds is also starting to build (you can follow the daily totals at BirdCast!). The plant sale coincides with peak spring migration, when millions of songbirds of dozens of species will be in the air. Some of these will be arriving in Delaware to breed, but most will be flying further north to breed in the vast forests across the northern United States and Canada. Most bird species migrate at night, for several reasons. It allows them to navigate using celestial cues, it minimizes their exposure to diurnal falcons which hunt on the wing, and it requires less energy as the wind usually drops. Unfortunately, this exposes them to a hazard with which they have had only a recent history: artificial light.
Artificial Light At Night (ALAN) is especially bright in the mid-Atlantic due to the proximity of several cities, including New York, Philadelphia, Washington D.C., and Wilmington. Birds migrating over brightly-lit cities or towns can become disoriented, distracted or confused by these lights, causing them to fly around in circles rather than continue overhead in a straight line. This causes them to waste the precious energy they need for their journey and may make them more likely to collide with buildings.
However, light pollution is not just a city problem. Even the relatively small amounts of artificial light present in suburban neighborhoods could affect birds, and not just during migration. Dozens of studies have shown negative impacts of light pollution on birds, with birds in illuminated areas starting to sing earlier in the day and earlier in the year, which could reduce their energy reserves. Light pollution also has negative effects on insects. Street and porch lights sometimes attract swarms of moths and other nocturnal insects which circle them and fly into them for hours. This drains their resources and may make them more vulnerable to predators like bats or frogs. A decline in these insects could have negative consequences for both migrating and resident birds which feed on them during the daytime.
Most people do not witness the negative impacts of night lights on wildlife because they do not spend much time outside at night apart from commuting or attending sporting events. However, 30% of vertebrates and 60% of invertebrates are nocturnal, and these animals have evolved with much less light to which they are currently exposed. This is also true of plants, and those near buildings or streetlights may be continuously exposed to bright lights for hours each night. There are several studies showing negative effects of artificial light upon plants and soil. Some of these are indirect, such as reducing the number of nocturnal insect pollinators, or disrupting their behavior so they do not visit plants when they are flowering. Other effects are direct, such as reducing the growth or development of plants in brightly lit areas or disrupting their natural photoperiod, so their flowers are not open when pollinators visit. ALAN can also affect the soil in which plants grow, by affecting the organisms present that are essential for nutrient cycling.
Awareness is spreading about the harmful effects of light pollution on birds and other wildlife and even human health and wellbeing. DarkSky International is a global initiative aimed at protecting the night sky through advocacy and education. DarkSky promotes simple measures any homeowner or building owner can do to reduce light pollution, including the Five Principles for Responsible Outdoor Lighting.
For example, most humans use some form of lighting outside of where they live or work – lights by their porch, garage, walkways, street or parking lot. This is understandable, as these lights provide safety and security. However, if these lights are downward-facing and fitted with a hood or shield, they can minimize the light spillover and how much they distract wildlife, especially birds migrating overhead.
A second widely used method to minimize light pollution is to use lights scheduled to only turn on when you need them, or motion-activated lights which only turn on when you pull into your driveway or take out your trash. These have the added benefit of reducing your electricity bill! A third simple step is to replace bright white lights with warm-toned yellow bulbs which are less disruptive to wildlife, such as these.
Taking these simple steps to reduce light pollution in your yard is a great way to help birds and other wildlife in addition to making your windows bird-friendly. If you really want to help wildlife in your yard all year round, we recommend you plant native wildflowers, bushes and trees to provide food, nesting sites and shelter. Come along to our upcoming sale and you are sure to find a plant you like!
Delaware Nature Society’s 2025 Spring Native Plant Sale will be held at Coverdale Farm Preserve in Greenville on Friday, May 2 (members only day, 2pm – 7pm) and Saturday, May 3 (public day, 9am-3pm). Click here for more details and the catalog!