Migratory birds are those birds listed as protected under the Migratory Bird Treaty Act (1918) (MBTA).

Currently, the U.S. Fish and Wildlife Service notes that some 836 species of birds are protected under the Migratory Bird Treaty Act, of which 78 species are listed as Endangered and 14 species are listed as threatened under the Endangered Species Act. An additional 144 MBTA bird species are listed on the Birds of Conservation Concern watch list, where populations are said to be declining precipitously.

Species protected under the MBTA include commonly hunted waterfowl, a wide variety of raptors, vultures, the California condor, crows, ravens, grackles, American woodcock and a large variety of seabirds.

Various causes of mortality to migratory birds include predation, disease, habitat loss and such anthropogenic causes as collisions with man-made structures (tall buildings, power poles, wind power turbines), poisoning (oil spills, pesticides), predation by feral cats, and “by catch” where sea birds are entangled in nets and long lines by fishermen based from U.S. ports.

Increased loss of habitat for migratory birds, notably waterfowl, can complicate environmental policy due to pollution of soils, riparian environments, and aquifers in the United States. For example, the proposed construction of unlined wetland “ponds” in the Imperial Valley of California, where phosphate and selenium saturation of the soils under the mitigation wetland is estimated to occur in as little as 4-5 years. Contamination could lead to violations of the “strict liability” language of the MBTA, something that is currently being evaluated by the U.S. Fish and Wildlife Service and various environmental groups.

Hunt for Truth is currently evaluating research papers alleging lead toxicosis in migratory upland game due to the ingestion of lead ammunition.