Shared Birds

One of the most striking results from the PIF conservation assessment was the large number of species that have a substantial proportion of their distribution and populations shared across national borders. These results underscore the complexity of the linkages among birds and habitats throughout their life cycle, across borders, and along migratory routes. With mounting threats, only increased and strategic tri-national cooperation can maintain this vital connectivity and protect sufficient high-quality habitats to ensure safe migrations for birds across the continent. For strategic cooperation, we need to understand how and where our birds are connected.

Birds Without Borders

Nearly half of the native landbirds (418 species) in Canada, Mexico, and the United States depend on habitats in at least two of the three countries. More than 200 species, which include more than 80% of all individual landbirds, inhabit all three countries in at least one season. These abundant species, most of them cross-border travelers, provide critical ecosystem services, such as pollination and insect control, which contribute significantly to our nations’ economic health. They require strong international coordination to monitor and protect them throughout their life cycle.

Our PIF assessment identified 272 species with at least one quarter of their range or population in at least two of our three countries, including 61 species with at least one-quarter of their population in each of the three countries (Figure below; Appendix D). These “substantially shared” species include 63% of the temperate-breeding species of highest trinational concern, as well as 64% of the common species in steep decline.

Full Life-Cycle Stewardship

Conservation of migratory birds requires actions that provide habitat and reduce mortality throughout the year. Habitat conditions in one season can affect the reproduction and survival of migratory birds in subsequent seasons. The quality of winter habitat can affect the timing of migration, leading to decreased survival or reproductive success. Therefore, actions to improve conditions in the tropics can have far-reaching positive effects on birds breeding in the United States and Canada. Conversely, because many northern breeding migrants spend up to eight months each year in tropical habitats, the health of these ecosystems depends on productivity of birds far to the north. 

Boreal Nursery An estimated 30% of North America’s landbirds (such as the Wilson's Warbler below) breed in the boreal forests of Canada and Alaska. Most depend on the tremendous seasonal surge of insects in summer, before leaving to winter in warmer regions. The boreal is one of the last and largest tracts of intact forest in the world. Recognizing the global significance of the boreal, Canadian federal, provincial, territorial, and aboriginal governments have established 50 million hectares of new parks and refuges in Canada’s boreal forests since 2000. Many of these protected areas use innovative new co-management models like that between Parks Canada and the Sahtu Dene community of Deline for management of 400,000 hectares near Great Bear Lake, Northwest Territories. The most productive and ecologically diverse parts of the boreal are under intense pressure for resource extraction, and any effects on bird numbers here are felt on wintering grounds in the United States, Mexico, and as far away as South America (www.borealbirds.org and www.borealcanada.ca).

Images: Wilson's Warbler, boreal forest by James Livaudais, Kenneth V. Rosenberg

This radar image from May 16, 1999, depicts a massive takeoff of birds from stopover habitat at the onset of nocturnal migration along the shores of Lake Erie (lower left) and Lake Ontario (upper right). The highest densities of birds are depicted in purple and red. Radar is a powerful tool for tracking bird migration and identifying important stopover habitats used during migration (www.fort.usgs.gov/radar/ ).

Mortality during migration may be 15 times higher for some species than during the relatively stable breeding or winter periods. Habitat loss at critical stopover sites is a major source of mortality. Throughout the annual cycle, anthropogenic threats, such as windows, tall lighted structures, wind turbines, indiscriminate pesticide use, and unrestrained cats can contribute to population declines. Protection of stopover habitats, especially along coastlines, mountain ridges, riparian corridors, and other migration pathways, is a high tri-national priority. This is especially true where the unique geography at the Cardel-Veracruz City corridor and the Isthmus of Tehuantepec in southern Mexico funnels billions of migrating birds through narrow corridors on their journeys north and south across the Western Hemisphere.

Click image to see large view of graphic

Linkages Among Habitats and Regions

Assemblages among the 272 substantially shared species from each major reeding habitat tend to winter in distinct regions of the continent. These strong linkages among adjacent and disjunct regions illustrate how the conservation of our shared birds depends on increased international cooperation. See Appendix
D for breeding and wintering habitats of shared species.

Arctic-Breeding Species

Grassland-Breeding Species

Photo by Chris Wood

Shared prairie birds, such as Chestnut-collared Longspur (left) and Sprague’s Pipit (right, typically winter in grasslands of southwestern United States and northern Mexico.

Photo by Bill Schmoker

Temperate Western Forest-Breeding Species

Boreal Forest-Breeding Species

Photo by Gerry Dewaghe

Shared breeders from the boreal forests, such as the Blackburnian Warbler (left) and Swainson’s Thrush (right), winter primarily in tropical highland and evergreen forests from southern Mexico to northern South America.

Photo by Greg Lavaty

Temperate Eastern Forest-Breeding Species

Photo by Gerry Dewaghe

Shared birds breeding in temperate eastern forests, such as the Prothonotary Warbler (left) and Summer Tanager (right), winter in tropical forests from southern Mexico and the Caribbean southward, with areas along the Gulf of Mexico being important during migration.

Photo by Greg Lavaty

Aridland-Breeding Species

Photo by Gerry Dewaghe

Forty-six shared aridland birds, including the Verdin (left) and Vermilion Flycatcher (right), tend to be year-round residents or short-distance migrants whose distributions span the southwestern United States and northern Mexico.

Photo by Kenneth V. Rosenberg