The Birding Year
May: Migration, Phase Two
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
This is the second in a monthly series of reflections and ideas on birding in the Pacific Northwest.
In May, eponymous Yellow Warblers with red streaks accenting their chest sing from freshly leafed-out trees. Wilson’s Warblers, the male all yellow with a black cap reminiscent of a yarmulke, sing from the woodland understory. The ethereal spiraling song of Swainson’s Thrush echoes in the forest. Willow Flycatchers call from their shrub-top perch. Western Bluebirds hop on a fencepost in the sun.
It is fully spring by May and these and other long-range migrants are arriving! The movement of millions of birds from the neotropics to North America is an event many birders anticipate all winter. The first two weeks of May is the peak period for waves of songbirds which move through the night sky as they fly northward. Warblers, flycatchers, orioles, tanagers, thrushes, and grosbeaks travel thousands of miles from Central and South America into the Pacific Northwest. Some will remain in Washington to nest. Most will move through on their way to the boreal forest and Arctic tundra.
NEOTROPICAL MIGRANTS
The neotropical biogeographical realm, one of eight such realms used by bird biogeographers, refers to the “new tropics” of Central and South America. During the period of European colonization of the Americas, the Western Hemisphere was considered the New World, as opposed to the Old World of Europe. The tropics of the Americas host an amazing array of bird species enriched millions of years ago during the great American biotic exchange when animals and plants mixed while crossing the Panama isthmus. The spring migrating birds have continued this pattern for over 5 million years.
The bird migration to the breeding grounds in North America annually concluded in time for newly hatched birds to meet the explosion of emerging insects in early summer. Flycatchers, blackbirds, and warblers are aerial insectivores, that is, they catch insects on the wing. Other birds specialize in eating the eggs and larvae of insects. Adult birds bring insects to young songbirds which require a steady diet of protein to develop quickly over just a period of weeks, before they themselves migrate south to the tropics.
WOOD WARBLERS: BUTTERFLIES OF THE BIRD WORLD
There are 55 species of wood-warblers in North America. Fifty are seen regularly in the United States and Canada and another five are in Mexico. They are characterized by their small size, spirited flight, bright colors, and beautiful songs. These warblers are highly specialized, insectivorous songbirds in the ornithological family Parulidae.
Ten of these warblers are common in the Pacific Northwest and they are distributed in a variety of environmental niches. For example, Black-throated Gray, Hermit, and Townsend’s Warblers are birds of the tree canopy and depend on healthy forests and woodlands. MacGillivray’s Warbler is reclusive and nests in the understory of mountain shrubs. Common Yellowthroat is a bird of the marshes, and Yellow and Wilson’s Warblers can be found in thickets of willows.
THRUSHES: DIVAS OF BIRDSONG
The true divas in birdsong are the thrushes of the family Turdidae. Swainson’s Thrush and Hermit Thrush are two of the best songsters among North American birds. There spiraling flute-like songs are truly heavenly and impart a feeling of peace during a walk in the north woods.
Townsend’s Solitaire is a lesser-known thrush which prefers higher elevation, but it migrates over a wide range and can be seen almost anywhere. Western and Mountain Bluebirds are birds of open woods and grassland. They nest in tree cavities and their population has been improved by the installation of nest boxes in areas where they breed.
CATCHING FLIES IN MID-AIR
Flycatchers, as their name indicates, are adept at snatching insects from the air. The large and varied flycatcher family Tyranidae contains some of the most active yet difficult to identify birds. Learning the flycatchers within their genus is helpful approach to understanding this group of birds almost all of which are neotropical migrants. For example, Olive-sided Flycatcher and Western Wood-Pewee are in the genus Contopus. These birds tend to sit on a prominent branch and sally out to grab insects on the wing, often returning to the same perch.
The Empidonax flycatchers are different. They are smaller birds of various shades of gray, brown, and buff and are notorious for being difficult to tell apart. There are five of these empids in various habitats in the Pacific Northwest. Western Flycatcher is a woodland bird that prefers riparian habitat along streams. This species name was recently returned to bird taxonomy and now includes both Pacific-slope and Cordilleran Flycatchers, which are no longer considered separate species. Willow Flycatcher, Hammond’s Flycatcher, Gray Flycatcher, and Dusky Flycatcher are four more Pacific Northwest empids.
Say’s Phoebe and the northward expanding Black Phoebe are placed in the genus Sayornis. Both of these birds will forage from a low perch and are common around human structures. All flycatchers depend on the availability of insects for their diet but will occasionally eat berries.
VIREOS AND BLACKBIRDS
The vireos are a less well-known group of neotropical songbirds and are most reliably identified by their songs. Warbling, Cassin’s, and Red-Eyed Vireos, all of the family Vireonidae, sing continuously especially in the initial stages of nesting. Vireos tend to be secretive and are well-camouflaged by their plain gray plumage. They are much less mobile than warblers and prefer to forage high in the canopy of trees.
In contrast the blackbirds in the family Icteridae are boisterous and competitive. These neotropical migrants include the marsh dwelling Red-winged and Yellow-headed Blackbirds, and the Brewer’s Blackbird of agricultural lands. In the past 25 years small flocks of Tricolored Blackbirds have expanded their range northward into Washington and nest in the Columbia Basin region. Bullock’s Oriole and Western Meadowlark are also part of the blackbird family. The oriole nests in black cottonwoods and the meadowlark is a grassland bird.
CHALLENGES TO MIGRATION
It is difficult to comprehend how birds weighing mere ounces can migrate thousands of miles, prepare for nesting, raise chicks, molt new feathers, and then make a return migration, all in a span of four to six months. The immense challenges of sustained flight in varying weather, finding food at stopover locations, confronting the loss of habitat and obstructions such as glass-walled high-rise buildings limit the success of many birds. We are fortunate that most survive the endeavor.
However, we now know from the multi-year bird population study led by Ken Rosenberg at the Cornell Lab of Ornithology that we have recently lost a significant number of birds. Published in 2019 the report documents that since 1970 one-third of the North American avifauna has been lost. That amounts to 3 billion fewer birds in North America. About two-thirds of the 3 billion birds lost in this time period were among migrating birds, especially sparrows, warblers, blackbirds, and finches. For reasons so far unknown, vireos and raptors have shown a modest increase in population. The report cites habitat loss, climate change, and unregulated harvest as contributing factors in the decline.
These losses indicate a fundamental alteration of our ecosystem which will require the involvement of many sectors of our society to set right. We are correct to fear the extinction of even a single species of birds, but the shocking reduction of substantial numbers of common birds is more devastating than the extinction of a single species.
HUMANS CAN HELP MIGRATING BIRDS
The boreal forest region of North America has less human habitation and still provides abundant flies, mosquitos, dragonflies, damselflies, and mayflies which provide a rich food source for all these migrating birds. Other areas, especially expanding communities, and agricultural regions where pesticides are in common use, have many fewer insects available for birds, leading to unsuccessful breeding seasons. Although we have a difficult task to protect birds today, past successes give us cause for some optimism. The challenge to help these birds is ours to accept.
In the recent past, banning the insecticide DDT led to the population recovery of the Bald Eagle, Peregrine Falcon, and Brown Pelican. During the same period of decline of Western Hemisphere songbirds, ducks and geese have shown greater numbers. The Cornell report credits this increase in waterfowl populations to adaptive harvest management and the investment of billions of dollars in wetland protection and restoration. These environmental accomplishments provide evidence that we can do as much for forest and grassland birds as we have done for water birds.
Birds with their amazing ability to overcome obstacles in their migration give us a good example to follow and can give us hope that by focusing our energy and money to support habitat recovery, we can improve the landscape for the neotropical migrating birds that nest among us each year.
SUGGESTIONS FOR FURTHER READING
Dunn, J. and Garrett, K. (1997). A Field Guide to the Warblers of North America. Boston: Houghton Mifflin. This book needs updating, but it is still the best all-around guide to warblers.
Lee, C. and Birch, A. (2023) Field Guide to North American Flycatchers: Empidonax and Pewees. Princeton: Princeton University Press. A new and well-produced guide to these challenging flycatchers. Remember that Pacific-slope and Cordilleran Flycatchers have now been re-lumped into Western Flycatcher.
Rosenberg, et al (2019) Decline of North American Avifauna. Science: Sept 2019. https://www.birds.cornell.edu/home/wp-content/uploads/2019/09/DECLINE-OF-NORTH-AMERICAN-AVIFAUNA-SCIENCE-2019.pdf
Stephenson, T. and Whittle, S. (2013). The Warbler Guide. Princeton: Princeton University Press. An identification guide with multiple photographs and sonograms for their songs.