Expert Series Part 5: Bird Friendly Glazing

Source: Guardian Glass

Did you know?...

Up to one billion bird deaths in the United States are attributed to collisions with buildings and other structures each year.* And we're heading into peak season.

The American Bird Conservancy partnered with the U.S. Green Building Council to incorporate solutions for bird-friendly architecture into USBGC LEED® (Leadership in Energy and Environmental Design) green building certification guidelines. The resulting USGBC Pilot Credit 55 is available for projects that develop a building façade and site design strategy that makes the building visible as a physical barrier to birds. Demand for bird-friendly glass is also driven by municipal and regional government requirements in a growing number of areas. As the architectural community and glass industry work to address this issue, it is critical for audiences to understand collision causes, product testing, bird behavior, and solution options. 

COLLISION CAUSES 

Cities with a density of building structures, including high-rise, can be the site of nighttime bird collisions due to interior and exterior lighting. Flocks of migrating birds can collide with large buildings and this generates headlines and attention. However, suburban, low-rise buildings account for a much higher percentage of collisions; individual collisions may not be as evident but can happen more frequently*. In general, there are four ways buildings and building environments contribute to bird collisions: 

Reflection: Birds cannot differentiate between actual and reflections of tree, sky, or habitat. Even lower reflecting glass can act like a mirror when it is bright outside and dark inside. When coupled with certain façade designs, the reflections can create areas that are visually confusing to birds. Reflective materials that provide adequate image formation, pose a danger to birds. 

Reflections can deceive birds into thinking that the glass is an extension of the environment. Trees and sky are replicated on the surface of the glass.

Transmission: When there is a direct line of sight from one window to another (e.g. walkways, corners, bus stops, or transparent wind/sound barriers), birds do not perceive the glass as a barrier, and may attempt to fly through, causing a collision. Also, birds can see wooded atriums or indoor plants as an inviting habitat. 

High light transmission of certain glass can also be a problem because birds can clearly see the environment on the opposite side of the glass; they may be drawn to pass through this structure making collisions more likely. 

Design: The design of the building and its location can have a significant impact on the collision risk as well as the maximum effectiveness of deterrents. Building shape, location, and landscaping (especially the anticipated height of the tree canopy once mature) all have considerable impact on the collision risk profile of the facility. 

Lighting: Birds use the night sky and ambient light levels to aid their migration navigation. This causes nighttime collisions as lighting inside buildings, especially those buildings with potential habitat, attracts birds. Artificial lights, particularly those that point upward, can lure and trap birds in their haze, where they potentially fly to the point of exhaustion. 

The interior and exterior lighting of this building could attract birds toward the building and increase the chances of collisions with the glass.

Product Testing and Bird Behavior 

Products intended to reduce or eliminate bird collisions can be tested for effectiveness. Evaluation takes time given they take place during seasonal migration, resulting in a limited number of tests and product configurations.

Before & After Retrofit Monitoring is the most definitive way to test a deterrent but also the slowest method in developing data for actual results. Monitoring can take place year-round, but numbers increase starting in spring and peaking in the fall. There are over 100 community and education-based local initiatives to collect this data in North America. 

SOLUTIONS

To mitigate effects of image formation on the façade, strategies for Bird-Friendly building design can be summarized in four categories: 

1. Reduce the glazing area: However, this can have other benefits and trade-offs related to energy performance and occupant views that should be considered. 

2. Utilize a physical barrier: Mounting exterior materials such as netting, mesh or decorative grills, and shading systems. 

3. Building shape and site design: Studies show that proximity to undeveloped land, agricultural areas, parks, steep grades, and water often correspond to increased bird populations and therefore increased risk of collisions. Consultants can help architects and designers by evaluating building plans for the impact that shape, layout, and fittings will have on bird populations. 

4. Incorporate glazing surface deterrence: The most important considerations for any glazing deterrence solution are the implementation of the 2x2 rule, maximizing visual contrast, and surface one deterrents. 

2x2 Rule (formerly 2x4) 

Birds are highly aware of their body size (like wingspan) and how they can safely navigate through a complex 3D environment. Hummingbirds are the smallest species that are highly affected by collisions - they will avoid flying through gaps 2” x 2”, in turn, coating or frit must meet these dimensions. This smaller spacing will also effectively deter birds with larger wingspans. 

Visual Contrast 

A pattern with smaller elements, smaller spacing, and greater coverage will be less visible from a distance than a pattern with larger elements, larger spacing, and smaller coverage. 

Clear No frit. The center glazing with the larger dots provides superior visual contrast as compared to the glazing on the right, with a tighter distribution of smaller dots.

Surface 1 Deterrents 

Placement of optimally spaced visual deterrents on surface one of a building’s glazing further augments detection by birds by minimizing the dilution of contrast when placed on surfaces two, three or four. NOTE: IGU glass surface numbers are identified by counting from exterior (surface #1) to interior (typically surface #4 for a standard insulating glass unit). 

Surface 1 Applications 

Reflection and Transmission issues can be resolved by adding a visual cue for birds, such as a UV coating or ceramic frit. Applications on surface 1 of an insulating glass unit have had the best results with real world monitoring. 

UV Patterned Glass 

Humans only see in the visible light spectrum. Some birds see in the UV spectrum in addition to the visible spectrum, UV coatings help prevent collisions by visually signaling an impending barrier. UV coatings provide another option for deterring bird strikes. Like frit or etch, UV provides a visual marker that can indicate a potential obstacle to birds. UV trades off some amount of effectiveness for dramatically improved aesthetics for humans. 

Bird Glazing Surface 1 Application

Coated Glass - Ceramic Frit

Coated Glass with Ceramic Frit or Acid Etch 

Ceramic frit is widely available solution for bird friendly glass. Frit patterns can be most economical solution in new projects. However, frit will tend to obstruct more of the occupant view than some other solutions. Fritted glass is most commonly used in new construction and is most effective to deter bird collisions when placed on the #1 surface. 

* Scott R. Loss, Tom Will, Sara S. Loss and Peter P. Marra, “Bird-building collisions in the United States: Estimates of annual mortality and species vulnerability”, The Condor: Ornithological Applications (January 2014) 

Please note: This information is provided as a convenience and is not to be construed as an assumption of responsibility or liability for design and application choices, which remain the responsibility of the design professionals involved in any project. It does not constitute legal advice, a modification of Guardian’s standard warranties, or an additional warranty of any kind.