The Birding Year in the Pacific Northwest

August: Post-breeding Dispersal

Written by Andy McCormick

Andy McCormick, Volunteer and Former Board President of Eastside Audubon

Common resident birds such as American Robins, Black-capped and Chestnut-backed Chickadees, Song Sparrows, and Dark-eyed Juncos are abundant in the Pacific Northwest. In August, there may even be more birds around. Young birds have fledged, and the total population of birds has increased as a result. As summer moves into fall these birds continue to show up at backyard feeders and local parks. At a glance, the birding world seems about the same as it has been since local songbirds began nesting in April and May.

But, when we listen, we notice that the birds are quiet. The mating season is over and bird songs are only a remnant of the spring dawn chorus. During the breeding period birds sing less and do not reveal the location of their nest. Birds will sing briefly in the morning, but it is a rare one that sings during the day.

Another population of birds, the neotropical migrating warblers, sparrows, orioles, and tanagers which arrived in spring, have been active away from the large population centers and out of sight of most humans. They have located suitable habitat, built their nest, and fledged young birds.

By August, most young birds are living on their own. Adult birds have completed their job of raising young as best they could and are now released from parenting obligations. It is time for migrating birds, both young and old, to focus their energy on completing their annual cycle of life and set out on their return migration to the south.

RETURN MIGRATION

In spring, migration is condensed into a few weeks in April and May. In fall, it is protracted. Some adult shorebirds begin migrating in July. In each month through the first half of October adults birds are followed by juveniles which most of the time migrate without parental guidance. They have inherited navigation ability to sense the magnetic field of the earth and to scan the skies at night. Most long-distance migrants move at night. Experience tells us this is to avoid predators.

The flight south varies among bird species. Not all birds make a direct flight to their wintering grounds. Some of these early migrants will stop along the migration route to attempt another breeding cycle. Others take advantage of a new food source and rest during a period in which they molt their feathers. Some seabirds make very long migrations to new feeding areas.

Four bird species: Western Tanager, Bullock’s Oriole, Brewer’s Sparrow, and Sooty Shearwater provide examples of varied migration patterns in August.

WESTERN TANAGER

The Western Tanager is a tropical-looking yellow bird with black wings. The male has an added feature of a red head. It was once common west of the Cascade Range, but it is now absent from most of the developed areas of the Puget Sound area. It favors Douglas fir forests at moderate elevation and much of its breeding habitat is east of the Cascades. This tanager is in the northwest region for only four to five months. It completes its breeding cycle quickly and adults and juveniles begin leaving the PNW by late July. This southward migration will peak around the Frazer River and adjacent mountains by mid-August. By early October, Western Tanagers will be wintering in Western Mexico and Central America.

BULLOCK’S ORIOLE

Bullock’s Oriole, another tropical-looking orange and black bird, arrives in the Pacific Northwest in early May and begins nest building in large deciduous trees, often favoring cottonwoods. Like the Western Tanager, the oriole has a short breeding period and will fledge young by July. It does not delay its migration and flocks of Bullock’s Orioles will be in peak migration in Oregon east of the Cascades by mid-August. This early departure allows Bullock’s Orioles to divert from their migration route to a stopover location in the southwestern U.S. for 60-70 days. The orioles then rest from the long flight and molt their feathers before continuing south to wintering grounds which range from Western Mexico to Guatemala.

BREWER’S SPARROW

The Brewer’s Sparrow is a fairly common, plain-colored bird of sage country across the drier areas of many western states. It is considered an obligate sagebrush breeding bird. That is, it requires sagebrush habitat for nest building and raising chicks. Central Washington and the Okanagon Valley in British Columbia mark the northern edge of its breeding range. (However, the subspecies known as the Timberline Sparrow will nest farther north into Canada and is excluded from this discussion.) Brewer’s Sparrow arrives in Central Washington by early April and is an active singer during the day sending its buzzy melody far over the sagebrush. Parent birds continue to feed their young for several days after they leave the nest and adults and young likely migrate together by early August.

However, some Brewer’s Sparrows will remain in the breeding area and attempt a second brood. These birds may not migrate until late September or early October. As more birds head south, Brewer’s Sparrows become common in the Mojave desert in September and most birds winter in the Sonoran and Chihuahuan deserts of the U.S. and Western Mexico.

SOOTY SHEARWATER

From the perspective of the Northern Hemisphere, we might consider the northward migration of the Sooty Shearwater as a “reverse” migration. However, this oceanic bird is at home in the Southern Hemisphere and breeds on islands off the southern tip of South America, Southeastern Australia, and New Zealand during the Austral summer in January and February.

By May, young Sooty Shearwaters have fledged and with the adults begin one of the largest mass migrations known. They disperse from the breeding grounds and follow a route across the open sea to the northwest of both the Pacific and Atlantic Oceans. By June, the Pacific birds are moving east ahead of the prevailing winds and arrive near the west coast of North America in August. As they continue northward, Sooty Shearwaters stay close to the continental shelf feeding on fish in the upwelling cold waters. The world population of Sooty Shearwaters is estimated at 20,000,000 pairs and in August and September enormous numbers of them pass by Ocean Shores, WA where they are visible from the jetty and shore. They continue north to their feeding grounds in the North Pacific and Arctic waters and will reverse direction to return to the southern islands and their breeding grounds by December.

PROTRACTED MIGRATION

Sagebrush Sparrows and Sage Thrashers, two other sage country birds, also vacate their breeding areas in August. Chipping and Vesper Sparrows and neotropical migrants such as Black-headed Grosbeak, Cassin’s Finch, and Lazuli Bunting will all be on the move. Warblers and flycatchers are two other families of birds which also begin their journey to the tropics in August.

In addition to Sooty Shearwaters, other shearwaters and petrels disperse from the breeding areas in the southern hemisphere and move northward following the Humboldt and other ocean currents in search of food. This trend has become stronger in the past decade as the oceans have warmed. Sightings of Brown Booby, Buller’s Shearwater, South Polar Skua, Red Phalaropes, and Long-tailed Jaeger have increased in waters off western North America.

There are challenges to birding in August. The weather can be hot and sticky and bird migration is protracted in fall and there are few large flocks to be seen. The departure dates for birds can vary from August to October. Neotropical migrants fly at night presenting another challenge for the birder. However, there are chances to see these and other birds in August. Many birds rest in the morning after night flying and getting out early can provide opportunities to find some resting birds before they take off to continue their flight south. Seabirds will be in motion and setting up a spotting scope for a sea watch can yield birds in flight over the ocean. Not all birds leave our area in August, and many will still be around. Nevertheless, if you miss them this year, make a note on your calendar to anticipate their departure next August to be sure you get out to see them.

SUGGESTIONS FOR FURTHER READING

Aversa, T; Cannings, R; and Opperman, H. (2020). Birds of the Pacific Northwest: A photographic guide. Seattle: University of Washington Press.

Lovette, I. J., and Fitzpatrick, J. W. (2016). The Cornell Lab of Ornithology handbook of bird biology, third edition. Chichester, West Sussex, John Wiley & Sons.