Lights Out to Save Migrating Birds
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
A conservative estimate of bird deaths from flying into building windows in the United States ranges between 365 to 988 million birds per year. This wide-ranging estimate reflects uncertainty regarding annual mortality because most studies are conducted during spring and fall migration. However, researchers conclude their “results support the conclusion that building collision mortality is one of the top sources of direct anthropogenic mortality of birds in the U.S.” (Loss, et al. 2014). This huge number of birds killed annually is second only to predation by domestic cats which kill between 1.4 and 3.7 billion birds each year.
In response to many studies like this one, the National Audubon Society coordinates a national network of 53 Lights Out programs which are designed to reduce bird mortality caused by birds flying into lighted windows at night. The Eastside Audubon Conservation Committee is currently reviewing the feasibility of the chapter initiating a Lights Out program on the east side of Lake Washington. To help the chapter assess its ability to conduct a Lights Out program, I set out to answer a few questions.
WHAT IS WORSE, THE AMOUNT OF LIGHT OR THE AMOUNT OF GLASS?
It appears that both the light and the glass are culprits in bird mortality. A study team in Minneapolis, MN (considered one of the top ten most dangerous cities for migratory birds) surveyed 48 building facades and measured the amount of artificial light at night (ALAN) and the amount of glass in each façade. They found that buildings with large areas of contiguous lighting attracted and killed more birds than smaller buildings or buildings with less lighted area (Loss et al. 2019).
However, a survey conducted in New York City’s Bryant Park (Parkins 2017) also calculated the number of lighted windows and the amount of glass in the façade of the building and found that the percentage of glass in the building was also important, because the glass can act as a mirror to reflect trees and open-air space, which appear as attractive flight paths to birds, drawing them to collide with the glass. Following morning surveys, the study found that few of the collisions occurred at night. Importantly, they reported that all of the dead birds found in their survey were migrating warblers and other migrating birds flying above tree level. Resident birds were not found among the dead birds near high-rise buildings. They do not fly high enough and may have become accustomed to urban life.
WHERE SHOULD A LIGHTS OUT PROGRAM BE SET UP?
A continent-wide study (Hager et al. 2017) including 281 buildings in 40 cities found that building size has a strong positive effect on bird-window mortality. Unexpectedly, the greatest loss of birds resulted from collisions with large buildings in areas of low urbanization. A large building among smaller buildings was apparently more lethal than buildings in highly urbanized areas. Birds may be better able to avoid areas of high urbanization with many tall buildings clustered together. The study concluded that a Lights Out program would be beneficial in cities and towns of all sizes, not just in large cities with high urbanization.
DO LIGHTS OUT PROGRAMS WORK?
I found many studies that document mortality of birds caused by lighted windows at night and misdirected bird flight into windows caused by reflection in the glass. However, there appear to be few studies of interventions to reduce bird mortality from building window strikes. Nevertheless, two reports indicate that intervention can help reduce this type of bird mortality.
A newspaper article (Soh 2014) reported on the Lights Out program in Washington, DC. There, a team requested a federal office building to turn off the lights at night during migration periods and in the first five years reported a two-thirds drop in the number of birds killed.
A more recent study (Groot at al. 2022) showed that two types of window treatments will reduce window strikes by birds. The team documented 71 collisions involving 17 bird species over four years. They monitored two buildings for two years to establish baseline data. Then windows in one building were treated with Feather Friendly ® markers arranged in a grid pattern, and the windows in the other building were replaced with UV-treated glass called ORNILUC Mikado. The markers reduced collision risk by 95%. The benefits of the treated glass showed a 71% reduction, but the result did not meet significance standards.
NEXT STEPS
This information provides some beginning data for consideration in developing a Lights Out program on the Eastside and our chapter should continue to explore such a program and our ability to conduct it. The chapter will need time to develop baseline data to determine the extent of bird mortality on the Eastside. If there is a problem, the program will need leadership to sustain it, and a survey protocol and recruitment plan for survey participants. Following leadership from National Audubon, a Lights Out program is an important program for the chapter to consider. The strategy is simple: by convincing building owners and managers to turn off excess lighting during the months migrating birds are flying overhead, the program helps to provide birds safe passage between their nesting and wintering grounds.