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WINDOW COLLISIONS
Window collisions are a major cause of bird mortality. The American Bird Conservancy estimates that close to 1 billion birds die of window strikes annually in the US. Already pressured with habitat loss, birds in urban areas also struggle to find refuge. As the urban built environment expands, local birds, migratory birds, diurnal, and nocturnal birds are all at risk of collision.
While local data on bird strikes is typically sparse, San Francisco passed a bird-safe ordinance in 2011. This ordinance addressed the use of glass on buildings. Other Bay Area jurisdictions, including Emeryville, Mountain View, Alameda, and Oakland have also incorporated bird-safe regulations into new construction and renovations.
Main Causes of Window Collision
Often birds are not able to perceive glass in the same ways humans can. This makes them susceptible to collisions with buildings in the urban environment. Unlike other causes of mortality, window strikes kill indiscriminately regardless of a bird's health, age, and species.
The two most common cause of collisions include reflections and glass flyways.
Reflections
Refelective surfaces often mirror the surrounding environement, misleading birds into thinking that the tree they see in the window is a real tree when in many cases it is not.
Flyways
Conditions in which the bird can see through a building to the other side can also be confusing as they will increasingly perceive the glass as non-existent in the same way that many humans accidentally do.
(Image Source: SCAPE)
The Argument for Bird Safe Buildings
In recent years there has been increased concern towards the sustainability of buildings, often through energy efficiency, adaptive reuse, and other architectural considerations such as the massing and orientation of a building. Advancements in building systems technology has allowed the profession to move towards a more ecologically conscious positioning, however, these moves are mostly benefiting humans.
Developing building standards that are also beneficial to birds is complimentary to already existing tactics, such as fritted glass and louvres over windows. This should be considered more heavily in all new construction. Paradoxically, full glass buildings that allow humans to feel a greater connection to the outside harms birds, reflecting the tension between the desires to appreciate and protect nature.
Poorly planned greening can lure birds to their death, and unless landscape architecture and architecture as a whole takes a moment to reconsider how specific design moves may ultimately end up hurting birds rather than help them, through increased bird mortality.
Areas of particular concern in Berkeley can be identified through urban density, building heights, and the area's adjacency to a well populated bird area, also called "stopover sites." Stopover sites are sites such as waterfronts, bird feeding areas, or areas adjacent to urban vegetation. These sites can be high risk zones for birds, which may traffic these areas more frequently.
Downtown Commercial District
high building density
UC Berkeley
mix between habitat and infrastructure
Berkeley Waterfront
located near heavily trafficed bird habitat
2023 Proposed Ordinance: Reducing Bird Collisions
Currently, the City of Berkeley is considering adopting Bird Safe Ordinance that would address glass usage in buildings. This ordinance would cover residential, mixed use, and non-residential buildings, as well as transparent buildings and features (such as balconies and greenhouses). All transparent material on these structures must be "bird-friendly," meaning that it fulfills one of the following (with language taken directly from the draft ordinance):
Threat Factor Rating. Material must be a product with an American Bird Conservancy Threat Factor Rating of 30 or less.
Patterned Glazing Treatment. Patterned transparent material must have certain characteristics, such as opaque markers that are within a certain distance from each other.
External Screens, Shutters, or Shading Devices. Panes with exterior screens, shutters or shading devices installed permanently over windows, structures, or building features such that there is no gap larger than 9 inches in one dimension.
Although the ordinance requires all windows, even small ones, must be bird-friendly, it provides time for this requirement to be phased in. For example, buildings having transparent material as less than 30 percent of their façade do not need to meet the requirement until January 2025. Similarly, affordable housing projects have until the same date to meet the requirements.
While the ordinance has grown from its previous versions to become more comprehensive in some ways (such as applying to windows of all sizes and more project types), it does not address existing windows that are not being replaced. These windows represent the majority of glass usage in the city.
In the past, San Francisco has subsidized residents to replace or treat large windows (larger than 24 square feet) to become more bird-friendly. Residential areas were of particular interest due to the proximity of neighborhoods to the city's parks and open spaces, which tend to attract birds.
However, windows do not necessarily need to be replaced to be bird-safe. There are a variety of other, less expensive treatment options available. These include bird safe films, screens, and tape, as well as blinds, curtains, and shades. A comparison of these costs are shown in the table below (source: Golden Gate Audubon Society). (Note that these costs were as of 2014, and likely have decreased since then due to increased availability.)
Nylon cords hung outside windows
25 cents / sq ft (DIY)
$2.50 / sq ft (premade)
Tape to pattern windows
34 cents / sq ft
Feather Friendly Bird Do-it-Yourself Tape
Tape to pattern windows
40 cents / sq ft
Window film that appears solid on the outside but allows views from inside
$3.25 - $6.60 / sq ft
Screens from BirdScreen.com
Fiberglass screen mounted on exterior windows
$69 cents to $1.83 / sq ft
Source: Golden Gate Audubon Society
Given the diverse and relative affordable nature of these products, having bird-safe windows is increasingly achievable for residents. However, these options may still not be financially accessible to all residents or building owners, whether due to being low-income or having multiple windows (such as an apartment complex).
Similar to San Francisco, we recommend that the City of Berkeley fund a subsidy program that identifies existing areas of high risk (i.e., proximity to parks) and prioritizes supporting low-income households and large residential building owners (10,000 square feet or more gross floor area, definition based on Berkeley's proposed Bird-Safe Ordinance).
To be the most effective, this recommendation should be implemented with accompanying public engagement measures, such as an informational campaign informing residents on options for creating bird-safe windows and a citizen science program (see: Community Engagement page).
Moving Past the Ordinance: Bird Friendly Urban Design
The invisibility of glass to birds is not the only cause for bird collisions. Much can be done through thoughtful urban design to the unnecessary death of birds. The location of water features, a projects proximity to vegetation, and the location of existing landscape features all play a part in birds flying in close proximity to buildings.
In addition, Berkeley's existing network of pathways offers a major opportunity to provide birds with food, shelter, and nesting sites, as well as safe passage for migratory birds as they journey through the city.
Bird Friendly Planning and Landscape
Identify bird attractions on site
vegetated streetscapes & urban parks
mature trees, shrubs, food sources and features that serve as habitat
attractions such as water features, nesting sites, or perching sites (roofs, covers etc)
Site buildings to minimize conflicts with existing landscape features
minimize the reflection of vegetation in windows and on building facades
isolate (existing) vegetation that is particularly attractive to birds
avoid the reflection of water on building facades on sites located near large bodies of water or water features
Create bird safe landscaping
place new landscapes away from glazed building facades or windows to prevent reflections
OR situate vegetation in close proximity to windows or glazing (3ft) so any reflections will be obscured
minimize the refelction of rooftop landscapes onto surrounding buildings
Source: SCAPE Bird Friendly Building Guidelines
Images: Bear Fountain Berkeley & Tree Reflected in Building Facade
Birdways through the City
The city's “municipal forest” includes 38,000 street, park and median trees maintained by urban foresters with the Parks and Recreation Department. But they are not distributed equitably: a series of "Tree-Equity Maps" produced by the national non-profit American Forests revealed stark contrasts in tree canopy between West Berkeley and more affluent districts to the east. In response Berkeley committed to an urban greening plan including 500+ new trees, primarily in the city's western neighborhoods.
But for birds, street median trees pose risks to many birds such as fast moving cars and proximity to glass windows of nearby buildings. Rather, birds need more secluded tree habitats.
Luckily, Berkeley has a rich network of pedestrian pathways and bicyle paths, many of which could become "Birdways" - areas of the city specifically designed with bird safety in mind, that offer birds places of refuge away from busy streetscapes and urban districts.
Case Study: West Street Pedestrian and Bike Pathway
The West Street Pathway runs along the former Santa Fe Railroad Right of Way between Cedar-Rose Park and Strawberry Creek Park. As seen in the image to the left, the pathway is only open to slow moving traffic such as pedestrians and cyclists.
Along the pathway there are a series of trees and downturned lights but many areas of the path remain relatively barren with limited vegetation and shrubbery.
As a way to develop bird safe pathways, the city should improve the vegetation found in these pathways as a means to provide shelter, food, and refuge for birds in the city.
By planting Birdways with native trees, shrubs and flowering plants, Berkeley's birds could enjoy food year round. Some of these plants include:
California Buckeye
Toyon
Elderberry
California Wild Grape
Coast Live Oak
Western Redbud
Manzanita
Western Serviceberry
RECOMMENDATIONS
Bird Friendly Buildings
Support a city-funded subsidy program for retrofitting unsafe windows by identifying existing areas of high risk (i.e., proximity to parks), prioritizing low-income households and large residential building owners (10,000 square feet or more gross floor area, based on Berkeley’s proposed Bird-Safe Ordinance).
Bird Friendly Urban Design
Planning and Landscape
Identify bird attractions on site such as vegetated streetscapes & urban parks mature trees, shrubs, food sources and features that serve as habitat man made attractions such as water features, nesting sites, or perching sites (roofs, covers etc)
Site buildings to minimize conflicts with existing landscape features minimize the reflection of vegetation in windows and on building facades, isolate (existing) vegetation that is particularly attractive to birds, avoid the reflection of water on building facades on sites located near large bodies of water or water features.
Create bird safe landscaping; place new landscapes away from glazed building facades or windows to prevent reflections OR situate vegetation in close proximity to windows or glazing (3ft) so any reflections will be obscured minimize the refelction of rooftop landscapes onto surrounding buildings
Developing Birdways
Enrich the greenswards adjacent to existing bike and pedestrian pathways with native trees, shrubs and flowering plants, to provide year round shelter, food, and refuge for birds in the city
Monitor Berkeley's Birdlife
Document all bird deaths. Donate specimens to authorized local bird conservation organization or museum to aid in species identification and for use in scientific studies, as per the Migratory Bird Treaty Act of 1918 (see page 10).
Encourage building management or maintenance crews to conduct daily sweeps of building perimeters, setbacks, and roofs to inspect for injured or dead birds.
Partner with local bird conservation groups to develop a districtwide monitoring program and corresponding LightsOut strategies.
Engage the Community
Create a bird friendly window information campaign on creating bird-safe windows.
Mobilize a citizen science program to monitor bird-window collisions.
Encourage volunteer participation in bird-collision monitoring.
Create an information campaign to inform residents, workers, and volunteers to temporarily care for injured birds before transporting them to certified wildlife rehabilitators.
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