The Birding Year
April: Migration, Phase One
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
This is the first in a monthly series of reflections and ideas on birding in the Pacific Northwest.
The focus of birding in April is on spring migration and a major transition in bird life in Washington. Our knowledge of bird migration is expanding with increased interest and research into the amazing distances covered by birds and how they find their way on these journeys. Migration patterns are changing in response to the warming climate. Some migrating birds are leaving Washington and others are arriving earlier in the year. Human development is impacting birds in migration. Expanding cities and towns and agricultural fields negatively impact important stopover locations along migration routes. Fortunately, birds are adaptable and can respond to some of these changes, but the challenges during a long migration are real.
THE ORIGINS OF BIRD MIGRATION
The annual movement of neotropical birds from Central and South America to the United States and Canada has been an annual event for millennia. The history of these migrations dates back at least 40 million years when the current continents began to separate from two enormous land masses. Today’s Africa, Asia, and North America were connected in one of them. Birds descending from this evolutionary line are considered Afroaves (Afro-áves). South America, Australia, and Antarctica broke from the land mass for the line of Austalaves (Austral-áves).
The gradual separation of the continents into the configuration we know today continued for about 35 million years. Between 13 and 5 million years ago, North and South America were gradually joined by the Panamanian isthmus, today known as Central America. As this joining process unfolded over several million years, the Western Hemisphere underwent the “great American biotic interchange” which altered the distribution of birds and other wildlife. Descendants of Afroaves from the north moved southward across the isthmus as descendants of Austalaves moved northward and led to a mixing of birds and other wildlife and plants. By this time period many of today’s birds had already evolved and expanded their range and some of them adopted a migratory pattern that continues today.
SHOREBIRDS IN TRANSITION
The birds of April are in transition. As wintering seabirds, raptors, and sparrows depart in the early weeks of April, neotropical warblers, tanagers, vireos, and orioles will be arriving as April turns to May. This amazing annual event involves millions of birds. In spring, bird migration is condensed into a period of about six weeks. Birds fly to their nesting habitats which range from the temperate to the arctic zones. Most migrating birds in the Pacific Northwest move along the Pacific Flyway making use of rest stops and refueling areas which are vital to their success in finding suitable habitat for nesting.
Coos Bay, Oregon, Ocean Shores, Grays Harbor, Stanwood, Samish Flats, and Bellingham Bay in Washington, and the coast of British Columbia provide excellent and important marshland and mudflat habitat for many shorebirds. North bound Western Sandpipers, Least Sandpipers, both Long- and Short-billed Dowitchers, Greater and Lesser Yellowlegs, and less familiar and more sensitive shorebirds such as Baird’s, Sharp-tailed, Pectoral, and Stilt Sandpipers and Red Knots all require healthy wetlands for their journey. While these shorebirds are passing through Washington, thousands of Dunlin, a shorebird which winters in the Puget Sound Region, will be leaving Washington and joining other shorebirds to breed in the Arctic.
RAPTORS, WATERFOWL, AND SPARROWS
In Central and Eastern Washington some wintering Rough-legged Hawks and Long-billed Curlews may still be present in early April, but they will be moving northward by mid-month. Thousands of Sandhill Cranes, which had arrived in the area around Othello, WA in March, will continue their migration throughout April. These cranes provide an example of the importance of rest and refueling habitat for migrating birds. They do not breed in Washington but use the grasslands for a period of rest and feeding to gain weight before breeding.
A major shift in the waterfowl population also occurs in April. Wintering Surf and White-winged Scoters, Common and Barrow’s Goldeneye, and Horned and Red-necked Grebes will be heading north. At the same time, Gadwall and Redhead (east of the Cascades) will join Mallards to nest around Washington. Marsh birds such as The Tricolored, Red-winged, and Yellow-headed Blackbird colonies will be settling in, and American Avocet, Black-necked Stilt, Virginia Rail, and Sora will all be arriving.
The mix of sparrows changes, too. Fox and Golden-crowned Sparrows depart, and Savannah Sparrows move in. Some of the earliest arriving migrants, Sage Thrasher and Brewer’s and Sagebrush Sparrows begin nesting in the sage country.
RESIDENT BIRDS
Resident birds in general get a head start on nest building and incubation of eggs as many get settled before the migrating birds arrive. Bald Eagles and Red-tailed Hawks began the breeding process in January and March respectively. While migrating Ospreys and Turkey Vultures arrive in late March and April to begin nesting.
Resident Song Sparrows, Spotted Towhees, Black-capped and Chestnut-backed Chickadees, Bushtits, Steller’s Jays, Red-breasted Nuthatches, and House Finches which have made it through winter will be singing to mark their territories and find a mate. Some of these birds will have begun nest building and incubation in late March and by the end of April some first broods may be hatching out.
KEEPING RECORDS
The observations of birders provide valuable information and insights into the changes in the migratory patterns of birds. Many birders keep a notebook where they record the spring arrival dates for birds. The eBird database at Cornell Lab of Ornithology collects data on bird observations all year long and around the world. Analysis of the data shows that birds in recent years arrive on the breeding grounds earlier in the year. April is a good month to be watchful for these changes in the bird behavior, and a great month in which to enjoy the diversity and resilience of these amazing creatures.
To explore and learn more about bird migration patterns, visit the Bird Migration Explorer.
If you would like to explore the world of bird migration in more depth, here are some suggestions for reading.
Heisman, Rebecca (2023). Flight Paths: How a Quirky Group of Pioneering Scientists Solved the Mystery of Bird Migration. New York: Harper Collins.
Kaufman, Kenn (2019). A season on the Wind: Inside the World of Spring Migration. New York: Mariner Books.
Weidensaul, Scott (2022). A World on the Wing: The Global Odyssey of Migratory Birds. New York: W.W. Norton.