Five ways to make bird migration safer
Spring bird migration across North America is now well underway!
In woodlots, fields, city parks, and backyards across the continent, our resident birds are being joined by hundreds of dazzling species that spent the winter in the Central and South American tropics. A visit to even the most marginal patch of vegetation on a foggy April morning is likely to yield a flash of colorful plumage or a burst of bubbling song. Although spring migration is a well-known and easily observable phenomenon to anyone who pays attention to the birds around them, almost no one sees the birds actually migrating – although we know birds fly northwards in spring, we generally don’t actually see them flying. How can this be?
Black-throated Gray Warbler
The remarkable fact is that the vast majority of migratory birds in North America – billions of individuals every spring – migrate nocturnally. While we often think of most birds - with the exception of a few specific groups such as owls - as being diurnal, this characterization is only accurate during the breeding and wintering seasons. During spring and fall, most migratory birds are active both day and night, voraciously eating during the daylight hours in preparation for flights of hundreds of miles under the cover of darkness. Nocturnal migration is such a massive phenomenon that almost every night during spring and fall, masses of flying birds are visible on weather radar at least somewhere on the continent. On overcast nights during the migration season, when birds are forced to fly close to the ground, you can even hear their flight calls if you step outside and listen carefully. Each species has a distinctive nocturnal flight call, and dozens of species may be audible on any given night. You can check this forecast to see when migrants are moving through your area!
It is important to note that the amazing spectacle of nocturnal migration has a dark side. Scientists are still trying to find out why, but as birds fly through urban areas, they are severely disoriented by the massive quantity of artificial light pollution that our buildings and infrastructure generates. Perhaps artificial light disturbs their night vision, or maybe birds rely on starlight for orientation, which makes the presence of additional light confusing. A vast body of scientific literature confirms that urban lighting draws in and “traps” birds within urban areas, causing them to fly around fruitlessly and tire themselves out. While within these areas, these birds are at an immense risk of crashing into various infrastructural hazards, especially windows.
The impact of light pollution on birds is difficult to overstate. Collision mortality, to which light pollution is a significant contributor, is the second-largest anthropogenic source of avian mortality (after predation by free-ranging cats) in North America, with hundreds of millions of birds dying in bird-building collisions annually. This mortality poses a serious threat to several species of conservation concern. For instance, around 10% of all Golden-winged Warblers, a highly threatened songbird currently declining in population, die in these types of collisions annually. Neotropical migrant songbirds, thanks to habitat loss, are already some of the most rapidly declining species on the continent – the last thing they need is the additional threat of light-induced mortality.
Luckily, light pollution is one of the most easily preventable threats to bird populations – in fact, individuals like ourselves can play a substantial role in preventing it while saving money on electricity in the process! The idea is incredibly simple – during migration season (between March and early June, and again between late August and November), we should limit our individual contributions to urban light pollution as much as possible. Such a reduction in lighting has additional benefits – light pollution is well-known to negatively affect various facets of human health, such as the circadian cycle, and it limits our ability to enjoy the night sky. So, how can we make such a reduction?
Step 1: Get rid of unnecessary outdoor lighting. This includes decorative lighting, as well as lighting that doesn’t serve a clear functional purpose. Not only is this type of lighting a significant contributor to light pollution, but it also wastes massive amounts of electricity.
Step 2: Make any necessary outdoor lights motion-sensitive. By installing a motion sensor that turns on lights only when they’re specifically needed, you can cut out the vast majority of unnecessary light pollution from your home every night and save energy in the process. Motion sensors also assist with security – a light suddenly switching on is often enough to make potential unwelcome guests wary.
Step 3: Switch out outdoor lights for dark sky-friendly fixtures, wherever possible. Certain types of targeted, well-shielded lighting can significantly reduce light pollution relative to common outdoor lights, such as flood lamps. You can easily find such types of lighting here.
Step 4: Turn off indoor lights in rooms that aren’t being used. Another simple, common-sense, energy-saving fix with no cost whatsoever.
Step 5: Roll down the blinds at night. You may already do this for privacy, but it’s worth a reminder. Although blinds don’t completely eliminate light pollution, they can significantly reduce light intensity.
Can’t take all of these steps every single night? No problem! The Cornell Lab of Ornithology’s BirdCast program uses weather data to forecast the intensity of bird migration across the contiguous United States every night during migration season. On nights when your local area is forecast to experience particularly heavy migration, BirdCast issues a local bird migration alert. You can check here every evening to see if an alert is in place for your area and if so, you can limit extra lighting on those nights specifically. That being said, it is still best practice to follow all five steps throughout the entire migratory season, as forecasts can be wrong, and there are always at least some migrants passing overhead even on spring and fall nights with low overall intensity.
The good news is that recent research has shown that even a modest reduction in urban light pollution can substantially reduce bird mortality during migration. If a significant number of us follow these five simple steps starting this spring, we can not only save energy and improve our own health but also allow for a safer migration for billions of beautiful birds, helping preserve the spectacle of spring migration for generations to come.
