Bird collisions are a major issue that affects millions of birds every year. Understanding the causes behind these often fatal crashes can help guide conservation efforts to prevent them.
Windows
One of the leading causes of bird collisions is windows. Birds fail to recognize glass as a solid barrier and fly directly into windows on buildings and homes. This accounts for up to 1 billion bird deaths per year in the United States alone according to Smithsonian estimates.
There are a few reasons why birds collide with windows:
- They see reflections of trees and sky in the glass, which tricks them into thinking they can fly through.
- Transparent windows do not present an obvious obstacle like a solid wall does.
- Windows mimic openings in a natural environment that birds would normally fly through.
Certain conditions make window collisions more likely:
- Feeders or vegetation near windows attract birds but also obscure their view of the glass barrier.
- Birds flying at higher speeds are less able to change course when they notice the window at the last second.
- Low-light conditions like dusk, dawn, and night lead to reduced visibility.
Types of Windows that are High Risk
There are certain types of windows that pose an especially high risk of bird collisions:
- Plate glass: Large, reflective panes of glass that offer unobstructed outside views for building occupants also unintentionally create deadly illusions for birds.
- Business parks: Clusters of office buildings glazed with plate glass claim high tolls during migration seasons.
- Noise barriers: Long partitions of glass or plastic erected along highways guide birds into oncoming traffic.
- Greenhouses: Glass walls and ceilings entice birds indoors where they become trapped and starve.
Window Type | Bird Collision Risk |
---|---|
Plate glass | High |
Business parks | High |
Noise barriers | High |
Greenhouses | High |
Communication Towers
Communication towers are another significant hazard for birds, especially those that migrate at night. Estimates range from 4 to 50 million bird deaths caused by towers annually in North America.
There are two main factors that contribute to birds colliding with towers:
- Tower heights and lighting schemes disorient migrating birds at night, especially in bad weather.
- Guy wires and cables surrounding towers are difficult to see and pose an unexpected collision risk.
Nocturnally migrating songbirds are most susceptible to tower collisions because they migrate in large numbers at night during spring and fall. They are drawn in by tower lights and may circle in confusion until exhaustion leads to deadly collisions.
Wireless Communications and Bird Collisions
The proliferation of wireless communications technology has increased the risks that towers pose to birds. Several factors related to modern cell phone and broadcast towers increase collisions:
- More numerous towers to meet demand for wireless services.
- Towers exceeding 1,000 feet in height to expand coverage.
- Red flashing aviation safety lights that attract night migrating birds.
- Broadband antennae that broadcast across wider sections of the spectrum.
The U.S. Fish and Wildlife Service estimates that 6.8 million birds die in tower collisions annually. Redesign and regulations for new and existing towers could significantly reduce this toll.
Power Lines
Birds also collide with power lines, which account for up to 175 million avian deaths per year in the U.S. according to Fish and Wildlife Service estimates. Electrocution is a danger posed by power lines, but collision is more common.
Several factors contribute to birds colliding with power lines:
- Poor visibility of thin lines against complex backgrounds.
- Lines at low heights across fields and wetlands intersect bird flight paths.
- Guy wires used to support poles create an unexpected obstruction.
Species most vulnerable to power line collisions include larger birds with low maneuverability and poor frontal vision such as swans, geese, cranes, herons, and pelicans. Raptors that scan for prey below them while soaring or flying low can also fatally impact lines.
Power Line Markings to Reduce Collisions
Marking power lines can help reduce collisions by alerting birds to their presence. Some effective markings include:
- Spiral vibration dampers that create movement and noise.
- Colored swivels and strips that contrast with the background.
- Aerial marker spheres spaced closely together.
Proper placement is important for reducing mortality. Markings are most effective when installed:
- Near wetlands, other bird habitats and migration routes.
- On guy wires and ground wires.
- At intervals of no more than 5-10 meters.
- On neutral/static wires which birds often collide with.
Wind Turbines
Wind power poses a collision risk for birds, but deaths are minimized with proper turbine placement and operation. The number of avian fatalities per megawatt hour is much lower for wind power than other energy industries according to research.
Factors that influence bird collisions with turbines include:
- Fast blade speeds at migration heights.
- Turbulence and air pressure changes that confuse birds.
- Lights that attract night migrating birds.
- Habitat loss from placement in sensitive areas.
Species most impacted by wind turbines are resident birds of prey and migratory songbirds. Careful wind farm planning can reduce collisions up to 70% by avoiding key migration corridors and habitats.
Minimizing Wind Turbine Impacts
The wind power industry has adopted guidelines and strategies to lower risks. These include:
- Siting turbines away from recognized bird migration corridors and wetlands.
- Avoiding ridge edges and narrow passes that concentrate migratory flights.
- Using minimum lighting on turbines and synchronizing flashing lights.
- Higher cut-in speeds so blades don’t turn at low wind speeds.
- Automated curtailment during peak migration.
Properly sited wind farms have little long-term impact on bird populations according to research, while providing wide-ranging environmental benefits.
Airplanes
Aircraft collisions with birds are less frequent than other categories, but often more immediately catastrophic when they do occur. These incidents threaten human lives as well as birds.
Key factors related to airplane collisions include:
- Jet engines operating at low altitudes during takeoff and landing.
- Flights paths that intersect migratory routes and wetland habitats.
- Reduced visibility at night and in bad weather.
- High speed collisions with large birds exceeding the impact resistance of aircraft components.
Aircraft collisions with birds tend to peak during annual migration cycles. Airports use radar, habitat management, and patrols to reduce risks.
Mitigating Aviation Collision Risks
Airports and aircraft operators take steps to minimize potentially catastrophic bird strikes. Some best practices include:
- Altering or suspending flight operations during heavy migrations.
- Restricting hazardous wildlife attractants near runways.
- Using noise makers and patrols to scare birds away from runways.
- Designing aircraft engines and parts to better withstand bird impacts.
Aircraft flight crews also receive intensive training on how to respond safely to bird strikes. Continued research and standards have reduced risks for both birds and air transportation.
Other Causes
While glass, towers, power lines, turbines, and airplanes represent the most significant collision threats, there are other causes of bird fatalities to consider:
Vehicles
Birds crossing roads and highways may collide with fast moving cars and trucks. Collisions tend to peak during fall and spring migration seasons.
Habitat Encroachment
As human infrastructure expands into natural areas, birds are faced with new obstacles and risks they have not adapted to avoid.
Disorientation
Artificial light pollution at night can disorient birds and cause them to crash into buildings. Mirrors and reflective surfaces also confuse birds.
Predation
Birds fleeing rapidly from raptors and other predators may not focus on what’s ahead, sometimes leading to collisions.
Conclusion
Bird collisions are an unintended consequence of human infrastructure and activities. Simple modifications and greater care for the habitats birds utilize can significantly reduce injuries and deaths. Understanding the factors that commonly contribute to collisions enables targeted preventative measures in each category.
Progress has already been made in identifying problem areas and implementing solutions like marking glass or suspending building lighting during migrations. Continued research and mitigation efforts focused on modifying infrastructure and equipment that pose collision risks can coexist with human needs and prevent hundreds of millions of avian fatalities annually.