Every night this month, thousands of long-distance travelers pass overhead while we sleep. They are birds on fall migration, flying at night from their North American breeding sites to their winter homes in the tropics. Migration is one of the riskiest events in a bird’s life; however, we make it all the more dangerous by peppering ancient migration routes with tall towers and artificial lights. These birds have evolved to follow the stars to navigate to their winter quarters; when it is cloudy, the true stars are obscured, but the city lights below look very similar and disorient migrating birds. On cloudy nights, thousands of songbirds get ‘trapped’ by city lights, eventually either colliding with windows or falling exhausted to the streets below to be picked up by the local cats and gulls.
A Toronto-based group called the “Fatal Light Awareness Program” (FLAP), has done pioneering work to alert the public to this issue, and to convince companies to turn off their office tower lights at night during spring and fall migration. However, tall night-lit towers are not the only threat to birds on migration. A recent study in the online journal Avian Conservation and Ecology by Machtans and colleagues (ACE) measured the impact of buildings on Canadian birds, and the results are surprising. They estimate that a staggering 25 million birds are killed in Canada every year through collisions with our buildings. The biggest contributor to these collision deaths are our houses! These account for 90% of the total annual mortality caused by window strikes. This amounts to 22.4 million birds killed by our homes per year! To put this in context, most (about 60%) of Canada’s songbird species have population sizes of less than 5 million (Partners in Flight).
The second-biggest contributors to collision mortality, after residential houses, are the low-rise buildings where the majority of us spend our work day. These buildings account for about 10% of the total window-strike mortality, or about 2.4 million birds. These numbers reveal that this issue is not just a big city, downtown problem. It is an even bigger problem where most of us live and work.
This fall migration, I am on a self-imposed, bird body-recovery duty on the university campus where I work. Each morning, I check for casualties of fall migration under the windows of campus buildings. I have found many more than I expected. Just around one building, I have collected 20 dead birds of 12 different species, including warblers, woodpeckers, sparrows and thrushes. And unfortunately, the death toll will likely rise as fall migration continues for another couple of weeks.
Connecticut warbler killed by striking the window of my workplace on university campus.
The morning of September 11, I found a small-scale tragedy. A rare and little-studied songbird, a Connecticut warbler (Oporonis agilis) lay prone on the gravel at the base of a window that interrupted its southward migration. It is estimated that 95% of all Connecticut warblers breed in the boreal forests of Canada, thus despite the misnomer, it is a truly Canadian bird, at least during the summer. In fall, Connecticut warblers migrate to South America where they spend our winter months; a total annual journey of more than eight thousand kilometers- impressive for a bird that weighs less than the two loonies in my pocket. My body bag for the Connecticut warbler is a Ziploc. I bag it and bring it back to the lab where it will be used to teach undergraduates in biology about anatomy and physiology, much like human cadavers are used to train medical students.
The problem with low-rise and residential windows is not that birds are attracted to the bright lights; they are drawn in by the migratory stopover habitat they need to fuel up and continue their migration southward. Forest patches, fallow fields, and even ornamental landscaping can provide insects and fruit that birds need to power their migration. Molecules from the insect in your backyard may be burned as fuel when a bird crosses the Gulf of Mexico into the tropics. Problems arise when vegetation reflected in glass looks like the next good patch to find food.
A hermit thrush (foreground) killed by striking a window reflecting nearby vegetation (left image) and a newly developed window film that disrupts surface reflections to reduce collisions (right image).
The good news is that because it is our homes and workplaces that are having such a heavy toll on migratory bird populations, everyone has the power to help reduce the 25 million annual bird deaths by window strikes. The practice of sticking one hawk silhouette on the inside of a window is largely ineffective, but there are many effective ways to prevent window kills. Anything that visually breaks up the outside surface of a window and reduces its reflectivity will make our windows look to birds like the solid objects that they are. The FLAP website contains lots of tips and products for making the windows of your workplace (FLAP work) and home bird friendly (FLAP home).
On York University campus, we are working to have windows outfitted with an exterior coating made up of small white dots (feather friendly) that break up the reflectivity that has duped so many songbirds this fall. We hope to have the first, bird-friendly building on campus, and later, the first bird- friendly campus in North America. Hopefully others will be inspired to follow suit.
But, what happens to migratory songbirds when they leave North America? My Liber Ero supported research focuses on figuring out the routes and tropical overwintering locations of Canadian birds at risk. In future posts, I will report on what I have learned so far by using new technology to track individual birds on their long-distance journeys to the tropics.