Peak of spring migration

George Walter

Jill Severn | The JOLT News

Last fall, I wrote about a new tool called BirdCast that ornithologists use to track the patterns and timing of bird migrations. As the screenshot shows, this tool provides interesting insights for spring migration. It seems that at midnight on May 1 there were some 322 million migrant birds in the air over the continental United States.

Live bird migration maps on Bird Cast

Courtesy of George Walter

Click here for BirdCast Live Migration Maps.

The counts are made at multiple stations using special radar. The site itself allows for tracking in real time for every date during the migration — this screenshot is just an example.

Why are the largest numbers in eastern North America? That’s likely because, first, fewer birds overwinter in the east because of harsh winter weather.  The dominant fall migration direction is to warmer areas, i.e. north to south, including across the Gulf of Mexico. And, of course, the reverse occurs each spring.

Things are different in western North America. First, there are simply not as many songbird species here. Researchers speculate this is because a high proportion of the area is mountainous and/or dry and desert-like. Also, in contrast to the east, the coast area west of the Cascade and Sierra mountains is relatively mild and thus fewer songbird species follow those long migration routes for winter survival.

Instead, in western North America, a number of songbird species follow an up/down elevation migration pattern, wintering in low coastal areas (like Thurston County) and migrating up into the nearby mountains as spring arrives.

Of course, we also have some species that migrate south/north. They are shown in the screenshot but in smaller numbers, and they are arriving right now. What species are they?

Warblers: These are small insect-eating birds with thin bills that inhabit trees and bushes. They’re headed after wintering in the southern U.S. and/or central Mexico. They are sometimes quite colorful, and males have a distinctive and pleasing song. The Merlin app can assist you in identifying the song of specific warbler species.

One of my favorites is the black-throated warbler. They live in coniferous trees and are arriving in our territory now. The male’s black and white plumage is distinctive. Another warbler up in those conifers is the yellow-rumped warbler. The Audubon subspecies is the most common breeder in our territory.

Commonly found in bushes and forest understory are also two similar species. The Wilson’s warbler is a yellowish green with a yellow face. The male has a readily visible black cap. You seldom actually see the orange cap on the orange-crowned warbler. The best way to describe this species is a plain greenish warbler with a looping trill vocalization.

Flycatchers: It’s not surprising that these species are migrants from central and southern Mexico since their prey is scarce in the winter here. There are many different types of flycatchers in Washington and three species, each with a thin bill and distinctive call, are common here in Thurston County. The olive-sided flycatcher is often seen, and heard, at the top of a conifer. The male’s call is usually transcribed as “Quick! Three beers!” Once you have heard it, you won’t soon forget it.

Olive-sided Flycatcher

Photo by Liam Hutcheson

Pacific-slope flycatcher.

Photo by Liam Hutcheson

The understory of those same conifers is the haunt of the Pacific-slope flycatcher (formerly called the western flycatcher). This is a small active bird, often flying out from a perch seeking prey, and then returning to the same perch. Its coloration is a drab olive above and yellowish below and it has two wingbars; its call resembles a wolf whistle, at least to my ears.

Willow flycatcher.

Photo by Liam Hutcheson

The third common member of this family is the willow flycatcher. It’s also small, but its preferred habitat is open areas where it sits on a prominent perch looking for prey. It also has wingbars, but it’s more brownish than greenish and has a light belly and chest. Its call is a distinctive “fitz-bew.”

Swainson's Thrush

Photo by Liam Hutcheson

Also arriving this week are three other interesting migrants. The Swainson’s thrush is migrating here from Central and Northern South America. It is not colorful — brownish with a slight rusty wash. But its song, beautiful fluting notes that spiral up the musical scale, is a distinctive sound of summer in Thurston County. They like edges of wooded areas and might be almost anywhere there is good brushy cover. You are more likely to hear them than see them in the woods.

Western Tanager

Photo by Liam Hutcheson

Black-headed Grosbeak

Photo by Liam Hutcheson

The final two birds, the scarlet tanager and the blacked-headed grosbeak, are both edge of forest birds and they both winter in central and southern Mexico. The males of these two species are quite colorful (see Liam’s photos). You can look for them at mid-height of coniferous trees and sometimes on the ground as they seek out water. The grosbeaks will visit summer seed feeding stations.

These first weeks of May are exciting times for birdwatching. It’s rare but possible that at anytime a migrant might plop down from the sky right in front of you.

George Walter is environmental program manager at the Nisqually Indian Tribe’s natural resources department; he also has a 45+ year interest in bird watching. He may be reached at george@theJOLTnews.com

Photos for this column are provided by Liam Hutcheson, a 17-year-old Olympia area birder and avid photographer.