What is the bird collision problem?

The bird collision problem refers to the phenomenon of birds fatally striking human-made structures, especially buildings with large expanses of glass. This issue causes hundreds of millions of bird deaths per year in the United States alone. Understanding the causes, statistics, and potential solutions for the bird collision problem is an important step in reducing the number of avian fatalities from building strikes.

What causes birds to collide with buildings?

There are several factors that cause birds to collide with buildings:

• Reflective glass – Glass buildings can reflect trees, skies, and other features that birds try to fly towards. This tricks birds into thinking they can fly through the glass.
• Transparency – Clear and untreated glass appears invisible to birds. They do not realize glass is a solid barrier and try flying straight into it.
• Lighting – Artificial lights, especially spotlights, can disorient migrating birds at night. They may become entrapped and fly repeatedly into lighted structures.
• Habitat reflections – Glass buildings situated near parks, water, or green spaces may reflect the natural habitat birds are trying to reach.
• Building heights – Tall skyscrapers can become obstacles in flight paths and migration routes.

Birds have vision systems adapted for their natural habitats. They do not easily distinguish glass from openings to fly through. The combination of reflection, transparency, and lighting tricks birds into attempting to fly into deadly sheet glass barriers.

What species of birds are most affected?

While over 800 species of birds in the US and Canada have been documented as fatalities of building collisions, some groups are more vulnerable than others:

• Songbirds – Small passerine species like warblers, thrushes, and vireos make up over 50% of collision deaths. They are abundant across North America with migration routes over cities.
• Hummingbirds – Extremely fast with low maneuverability. They are drawn to enter reflections of plants and get trapped by glass.
• Woodpeckers – Specialized beaks and head anatomy make them prone to concussions against windows. This can cause immediate death or predators to catch them while dazed.
• Waterfowl – Groups migrating at night over lit urban areas become disoriented and crash into buildings.
• Raptors – Hawks, falcons, and owls focused on prey can accelerate rapidly towards glass hunting perches and collide at full speed.

While all birds are vulnerable, these groups suffer disproportionately higher mortality from building collisions due to their abundance, anatomy, and behaviors.

How many birds die from building collisions each year?

Estimates vary, but hundreds of millions of birds are killed by building strikes in the US every year. Some key statistics:

• 365-988 million – Estimated annual collision deaths in the US (Loss et al. 2014).
• 234,000 – Estimated average annual mortality just for the city centers of Chicago and New York City (Loss et al. 2014).
• 100 million – Estimated annual deaths in the US during migration seasons (Arnold and Zink 2011).
• 1 billion – Estimated annual bird collision deaths in the US, factoring in undercounting bias in surveys (Klem 2009).

These figures indicate building collisions are one of the leading causes of bird fatalities nationwide. The true number is likely over 1 billion annually when underreporting, inconsistencies, and lack of data are accounted for.

Which cities have the most bird-building collisions?

Major cities with large populations, high-rises, and location along migratory flyways see the highest rates of bird-building collisions. Chicago and New York City consistently top the lists for most collisions.

Other cities seeing high collision rates are Toronto, Washington D.C., Baltimore, Philadelphia, and Detroit. Cities located along Atlantic and Pacific flyways during migration have exceptionally high mortality.

What are the deadliest buildings for bird collisions?

Specific buildings with large glass expanses, location near parks/water, and lighting are responsible for huge numbers of collision deaths annually:

• Javits Center, New York City – Estimated 1,000-2,000 deaths per year
• Viracon Manufacturing Facility, Minnesota – Estimated 1,000+ deaths per year
• One World Trade Center, New York City – Estimated 500-800 deaths per year since opening in 2014
• U.S. Bank Stadium, Minneapolis – Estimated 300-500 deaths in first 2 years after construction
• McCormick Place, Chicago – Hundreds of deaths per year

Research has connected individual buildings with over 1000 annual collision deaths. These are often brand new constructions utilizing expansive glass panes near migration routes or ecologically attractive sites.

During what seasons do most collisions occur?

Bird-building collision rates fluctuate through the seasons with migratory patterns:

• Spring – Hundreds of millions migrate north in March-May. Exhausted birds reaching cities collide with buildings.
• Fall – Hundreds of millions migrate south in August-October. Young birds on their first migration are especially vulnerable.
• Summer – High activity around nesting sites leads to collisions with nearby buildings.
• Winter – Resident birds collide with buildings during foraging and storms.

However, collisions occur year-round, with spring and fall migrations being the deadliest periods claiming over 90% of annual collision fatalities.

Why is the bird collision problem increasing?

Though birds have been colliding with human structures for centuries, urbanization and architectural trends are causing a major surge in recent decades:

• More high-rises – Tall glass buildings within migration routes lead to more collisions.
• Increased glass use – Modern architecture utilizes larger glass panels which birds fail to recognize as barriers.
• Brighter night lighting – Birds are attracted to and disoriented by brilliant light installations.
• Urban expansion – Developing areas encroach on natural habitats, putting more birds in collision courses.

As major cities expand outwards and glass-heavy skyscrapers proliferate, the factors causing bird window strikes are increasing exponentially.

What are the effects of bird collisions beyond mortality?

Beyond the hundreds of millions that die outright from building hits, such collisions have other detrimental and cascading ecological impacts:

• Injuries – Birds that survive may suffer injuries inhibiting migration, breeding, or foraging.
• Predation – Dazed and injured birds are easily caught by urban predators like house cats.
• Population effects – For threatened species, building collisions hasten declines toward extinction.
• Ecosystem impacts – Loss of birds diminishes pollination, seed dispersal, and other ecological services.

Mass bird die-offs also have emotional impacts on the public. People are distraught witnessing deadly window strikes, which have increased massively in recent generations.

What can be done to reduce building collisions?

There are several strategies architects, planners, and conservationists recommend to reduce deadly bird-building collisions:

• Minimize glass – Use less glass overall, divide large glass expanses with mullions or patterns.
• Treat glass – Apply films, fritting, frosting, angled panes and other markers so birds recognize glass as a barrier.
• Reduce reflections – Situate glass away from nearby vegetation and landscapes that birds may try entering.
• Downshield outdoor lighting – Keep necessary lights shielded and directed downwards to reduce disorientation.
• Turn off unnecessary lights – Decrease light pollution in cities by extinguishing excess nighttime lighting.
• Retrofit problem buildings – Add anti-collision treatments to deadly existing structures like convention centers.

Adopting bird-friendly architecture standards for new constructions and modifications to retrofit problem buildings can greatly reduce mortality from collisions nationwide.

Conclusion

Hundreds of millions of birds are killed in building collisions annually as modern architectural trends increase fatalities. Songbirds, hummingbirds, woodpeckers, and other species suffer disproportionately due to anatomical and behavioral factors. Collision rates spike during migration seasons in deadly cities located along flyways. Expansive glass panels and artificial lighting are major culprits in increasing deaths. While addressing this issue presents challenges, a combination of policy changes, retrofits, and bird-friendly construction can make buildings safer for avian life.