Threats to Birds

Migratory Bird Mortality - Questions and Answers

Migratory birds face numerous threats throughout their annual cycles from both natural and human-caused sources. The U.S Fish & Wildlife Service is working with governments, conservation organizations, industry, and the public to reduce threats across the North American landscape to preserve our birds for future generations. There also many easy ways anyone in the general public can help protect birds around your communities.

What Are the Threats to Birds?
Many of the 1,027 species of birds protected under the Migratory Bird Treaty Act are experiencing population declines due to increased threats across the landscape. Of those 1,027 species, 92 bird species are listed as either threatened or endangered under the  U.S. Endangered Species Act. An additional 274 species are listed as Birds of Conservation Concern, in one or more geographic scales (e.g., local, regional, or national).  For more information about bird declines in the U.S., visit the  State of the Birds webpage.

Both natural and human-caused sources of bird mortality contribute cumulative or combined effects to declining bird populations. Millions of acres of bird habitat are lost or degraded every year due to development, agriculture, and forestry practices. These rapidly accelerating impacts can be mitigated only through habitat restoration and protection. In addition, millions of birds are directly killed by human-caused sources such as collisions with man-made structures. Death from natural causes is also common sources of mortality.

Natural and human-caused mortality impacts are exacerbated by the landscape alterations resulting from a changing climate. Birds in every habitat will be affected by natural and human-caused sources, so conserving migratory bird populations requires a multi-faceted, coordinated approach by governments, conservation organizations, industry, and the general public.

How Many Birds are Killed?
True estimates of mortality are difficult to determine. However, recent studies have synthesized the best available data to estimated ranges of mortality to bird populations in North America from some of the most common, human-caused sources of bird mortality. These are listed in the table below. This list addresses only human-caused sources, not natural sources. Many additional human-caused threats to birds, both direct (causing immediate injury/death) and indirect (causing delayed negative effects to health or productivity) are not on this list because the extent of their impact is either not currently well researched or easily quantified. For instance, habitat loss is thought to pose by far the greatest threat to birds, both directly and indirectly, however, its overall impact on bird populations is very difficult to directly assess. Other common human-caused and natural threats to birds that are known, but not listed below include various entanglement and entrapment threats (e.g., open pipes and nets); predation by other animals besides cats, including humans (e.g., poaching); weather events; starvation; and disease.

Top Common Human-caused Threats to Birds (U.S. only. Ordered by Median Estimate of Bird Mortality Annually.):

Hazard/Type Min Range Max Range Median/Avg. Estimated
Cats 1,400,000 3,700,000,000 1,850,700,000
Collision - Building Glass 365,000,000 988,000,000 676,500,000
Collision - Vehicles 89,000,000 340,000,000 214,500,000
Poison     72,000,000
Collisions - Electrical lines 8,000,000 57,000,000 32,500,000
Collisions - Communication towers     6,600,000
Electrocutions 900,000 11,600,000 6,250,000
Oil Pits 500,000 1,000,000 750,000
Collisions - Wind Turbines 21,000 679,000 328,000

Sources of mortality estimates: Longcore et al 2012 (communication towers); Trail 2006 (oil pits); Loss et al, Smallwood, Erickson et al (wind turbines); Loss et al (all other).

What is the U.S. Fish & Wildlife Service Doing to Reduce Mortality?
The Fish and Wildlife Service mission includes working with others to conserve natural resources. The many successful bird conservation initiatives the Service is a part of with partners are shining examples of how multi-organization collaborative partnerships can lead to conservation success.

In addition, the Fish and Wildlife Service provides information and assistance to industry and public seeking to develop projects in a manner that reduces impacts on birds and their habitats. Some of the resources the Service provides, and is constantly improving upon, are voluntary guidelines, best practice recommendations, and information and resources for developers for conducting environmental reviews striving for bird-friendly projects. This information empowers the public to understand potential impacts from various activities and provides recommendations on how to avoid or minimize those impacts. In addition, web-based applications are in development to make access to bird data,  project planning information, and other decision support tools more easily and readily available to biologists, developers, and others that need them for facilitating decision-making where bird conservation is concerned.  Finally, the Migratory Bird Program offers training for industry and partners to help understand their legal responsibilities; know where to go to obtain the information and tools needed for successful bird conservation; and understands the benefits of partnerships and how to more actively take advantage of partnership opportunities.

How Can You Help?
Everyone can help protect migratory birds.  Whether it is taking actions around your home or workplace, designing bird-friendly projects, or just taking actions that reduce resource consumption, every action is one step towards protecting migratory birds for future generations. A few simple actions that can be taken include:

Migratory birds are among nature's most magnificent resources. Their conservation is a critical and challenging endeavor for the Migratory Bird Program and all who value nature. If you need immediate assistance, contact the Migratory Bird Program at migratorybirds@fws.gov.

Last Updated: April 18, 2018