Avian Amicable Architecture

by Marcy Marro | November 1, 2019 12:00 am

A recent study led by Cornell University and American Bird Conservancy[1] (ABC) and published in the journal Science[2] estimates that the North American bird population has declined by 29 percent (almost 3 billion birds) since 1970. Anthropogenic habitat destruction (development, agriculture, pesticide use, and climate change) is likely the largest contributing factor, followed by outdoor domestic cats, which kill an estimated 2.7 billion birds per year in the U.S. The third largest factor is window collisions, accounting for approximately 600 million bird deaths annually. Wind turbines are often cited for bird deaths, and some poorly situated wind farms have had impacts on certain species, but the overall impact is orders of magnitude smaller than the top three noted above.

While sustainable development and high-performance building design can reduce or mitigate habitat destruction, designing bird-friendly buildings is the most direct means for building professionals to reverse this disastrous trend. Recognizing this, at least eight North American cities, including San Francisco, Portland and Toronto, as well as Cook County, Ill., and the State of Minnesota have adopted bird-friendly building ordinances, with proposed laws pending in multiple other cities. Let’s review why bird collisions with buildings happen and what it means to be a bird-friendly building, and then explore some specific solutions.

Avian Physiology and Behavior

As human development spreads farther into natural areas, both resident and migratory bird populations become more likely to come in contact with buildings. Birds use vegetated corridors to get from one part of their habitat to another, and this includes tree-lined streets and parkways. It is here that buildings become deadly because birds don’t perceive glass the way that humans do. Depending on the type of glass and the light conditions, it will either be invisible; inviting them to fly through to the other side of the building, or it will mirror the adjacent trees and sky, appearing as a viable flight path. Exacerbating these phenomena is the fact that birds are photophilic. Migratory birds primarily travel at night, using celestial cues to guide them, and light pollution from cities interferes with their navigation, drawing them in where they face a greater hazard of window collisions.

What Makes a Building Bird Friendly?

The good news is that there are simple things that architects can do to reduce the chances of bird collisions. Many of these are outlined in the USGBC’s LEED Pilot Credit SSpc55 Bird Collision Deterrence[3]. These design strategies include:

• Reducing window area, especially within the three floors closest to the ground (or vegetated roof areas).
• Specifying marked bird-smart glazing with a collision Avoidance Index (AI) of 70 percent or higher (see below).
• Avoiding unmarked glazing in high-hazard location, including guardrails, skybridges and transparent building corners.
• Reducing light pollution, including minimizing outdoor illumination, using Dark Sky Friendly fixtures[4], turning off interior illumination after hours, and avoiding blue-rich white light sources (>3,000 Kelvin).

Bird-Smart Glazing

To address the primary cause of bird collisions, unmarked glass, American Bird Conservancy developed a test[5] to rate glazing products and established an AI for each. Their tunnel test compares the subject glazing to a clear glass baseline, recording the behavior of birds flying toward them (no birds are harmed in the conduction of the test). While no glazing is 100 percent safe for birds, products that achieve an AI of 70 or higher can be labeled “Saves Birds Tested.”

There are two primary means of marking glass to create glazing that can achieve this rating. The first is adding a visible etched or printed pattern on the outer light of glass. An exterior applied film can achieve a similar effect in retrofit situations. A second option involves a special factory-applied coating on the outer light that reflects ultraviolet (UV) light to reveal a pattern. Human vision is limited to the visible light spectrum, but birds can see UV light, so markings on glass with this coating are visually imperceptible to people looking through a window but appear as an obstacle to birds.

Markings on bird-smart glass can be geometric, typically an array of dots or a series of horizontal or vertical lines, or more organic patterns. The key is to follow the 4 x 2 rule, meaning the spacing between markings is no more than 4 inches horizontally or 2 inches vertically, matching the narrowest spacing between tree branches that birds may fly through. Markings on the number one surface of the glass (the exterior surface of the exterior light of an insulated glazing unit) are most visible to birds, while markings on the number two surface can be veiled by reflections on the outer surface in some light conditions, making them less effective.

Some of the ABC tested glazing products with AI over 70 include:

• Walker Glass[6], Aviprotek acid-etched glass, and Aviprotek T UV reflective pyrolytic coating
• GlassPro, Bird Safe Glass[7], UV reflective coating
• Arnold Glas, Ornilux Mikado[8], UV reflective coating
• Guardian[9], Bird1st, UV reflective coating, and SunGuard SN 68 fritted glass
• Viracon[10], silk-screen patterned glass

While these products generally have a cost premium compared to typical high-performance glass, the cost is coming down, especially with more North American manufacturers coming online. There are two ways project teams can manage costs and still mitigate bird collisions. First, architects can specify bird-smart glass only for the high-risk portions of the building (e.g., lower floors, corners, guardrails, etc.), using standard glass for the remainder of the building. Secondly, even with high-performance glazing, large areas of glass reduce energy performance and don’t necessarily improve daylighting. Limiting the window-to-wall ratio in the façade design reduces bird collision risks and the total cost premium associated with bird-smart glass, while also improving thermal and visual comfort and energy performance.

With mounting awareness of the serious threat to avian populations, and the increasing number of laws addressing this problem, it is incumbent on architects to proactively adopt bird-friendly design strategies. Fortunately, design guidelines[11] and glazing products are available to support the design of beautiful, bird-friendly buildings.

---

Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with over 30 years of experience in sustainable building design. He is a senior consultant with Intertek, Building Science Solutions in Portland, Ore. To learn more, visit intertek.com/building/building-sciences[12] and follow Scott on Twitter @alanscott_faia[13].

Source URL: https://www.metalarchitecture.com/articles/avian-amicable-architecture/

---