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When you are a birder, every season is marked by the appearance of a certain species or exciting avian events. Yet, if you were to ask most birders what they look most forward to, many would answer "spring migration."
For each of us there is a species that signifies the onset of the spring songbird migration. Many Oregon birders might tell you that the arrival of the first Rufous Hummingbird–a species that usually reaches the southern Oregon coast by mid-February–signals the start of the northbound migration season.
Having spent my formative birding days in the Midwest (northern Indiana), spring migration means one thing...warblers! February is still Winter in my view. I don't feel like spring migration has arrived until the bigleaf maples are blossoming and I see my first Black-throated Gray Warbler. Granted both Oranged-crowned Warbler and Common Yellowthroat arrive a few days earlier, but they can't match the eye candy appeal of a Black-throated Gray. I see a few Orange-crowneds each winter, so my first spring migrants are generally not year birds. Common Yellowthroats are often heard but not seen when they first arrive. They tend to stay buried in wet grassy habitats that don't necessarily evoke the emotions associated with seeing trees starting to leaf out and blossom. Seeing that first crisply patterned male Black-throated Gray hopping from branch to branch in a tree that only days earlier was stark and leafless triggers excitement.
Anticipation seems to be the element of spring migration that has a hold on us. Every spring, questions arise about arrival dates for the many neo-tropical species that nest in western Oregon and pass through our region on their way to more northerly breeding grounds. "When will the first tanagers show up?" When can I expect to see Wilson's Warbler?" There are several excellent phenologies for western Oregon already available online (see below). They offer lists of average arrival dates for a rather specific area. Some also include the earliest spring arrival dates the area covered. Understanding the arrival order of your local neo-tropical migrants serves to enhance the anticipation of 'FOS' (first of season) birds. Over time you'll come see a date on the calendar and think, "today, I should see or hear my first...
As the annotated list below suggests, migration phenology is not an exact science, but the first detections for most species do tend to fall within relatively consistent windows year after year. Occasional weather anomalies may produce modest adjustments in the schedule, but it is somewhat rare for spring arrivals to come more than a week earlier or later than normal.
Global climate change is the one big unknown and it should motivate us to pay close attention to how migratory birds respond. Numerous studies, mostly involving plant phenologies, clearly demonstrate that 'biological spring' is coming several days earlier than it did fifty years ago. It is hard to imagine that birds will not gradually adjust their migratory schedules and breeding ranges based on when plants flower and where they grow in the future. For many of the insectivorous birds, arrivals seem to correspond with the blossoming of certain plants or the leafing out of particular trees.
Until I started using eBird about four years ago, I never consistently recorded my personal arrival dates. However, I have paid close attention to spring arrivals and I have memorized the typical arrival dates for the Willamette Valley, which to this point haven't changed much since I started birding seriously in 1977. Below is a phenology that includes some commentary about what I've learned over nearly forty years of observations and active birding during spring migration.
Note that much of my spring migration birding has been done around Eugene, thus the dates that I offer below are skewed by observations from Lane County and the southern Willamette Valley. If you live farther north in the Willamette Valley, the arrival dates for Eugene may be as much as 5-7 days earlier than the arrival dates for the Portland area. This phenology will not be particularly useful if you live east of the Cascades, where the spring leaf out and arrival dates are later for most species.
This list includes the expected and a few less-expected Willamette Valley migrants and focuses on those that arrive 20 March or later. I chose not to include Rufous Hummingbird, swallows, and some of the eastside species that stray west of the Cascades annually (i.e. Say's Phoebe and Mountain Bluebird). I also chose not to include several species of sparrows that in addition to wintering in western Oregon also have a conspicuous migration that passes through western Oregon. I've included photos of several species and some comparative discussion of Hammond's, Gray, and Dusky Flycatcher.
Olive-sided Flycatcher -- First arrivals usually in the last few days of April or the first few days of May. I think my earliest is 25 April.
Western Wood-Pewee -- First week of May. I can't recall having ever seen this species in April. There are often early 'heard only' reports of this species that come from mid-April or even earlier. These reports are the work of European Starlings. I've always found it interesting that starlings don't seem to mimic pewees very often during winter, but as Spring approaches this seems to be their go-to imitation and they are remarkably good at it.
Willow Flycatcher -- Rarely seen in the Willamette Valley before the second week of May. I've never seen or heard this species in April and I don't recall having seen a Willow earlier than 9 May. At Skinner Butte in Eugene, migrants are often conspicuous into the first week of June (they don't breed on the Butte).
Hammond's Flycatcher -- In years when I have been able to be out birding spring migrant traps daily, I always found this species by the 15th of April, with my earliest detection coming on the 10th of April. Late in the second week of April is a pretty consistent window for the arrival of this species. Learning the fairly loud call note of Hammond's will increase your early season detections. Hammond's generally stay fairly high up and inside the canopy.
Gray Flycatcher (westside) -- Over the past 30 years, Gray Flycatchers have proven to be an extremely low density spring migrant west of the Cascades. "Detroit Flats" (at Detroit Lake) east of Salem has consistently yielded reports of this species when it has been covered. Back in the 1990's and early 2000's Steve Dowlan, who now lives in Pennsylvania, found Grays at Detroit Flats annually. Coverage there has been spotty since Steve moved away, but in April 2014 Roy Gerig and others made several trips to this site and encountered multiple Grays there during each visit. Gray Flycatchers are now found nearly every spring on Skinner Butte in Eugene and at Portland's Mt. Tabor Park. Westside Grays normally appear during the last week of April or the first week or so of May. Gray and Dusky Flycatchers can be tough to tell apart, as their proportions and plumage are nearly identical. Their similar whit call notes, their primary vocalizations during migration, take a sharp ear to differentiate.
Dusky Flycatcher (westside) -- This is a low density migrant in the Willamette Valley and presumably in the Rogue and Umpqua Valleys as well. In terms of timing, Duskies are very similar to Gray Flycatcher, with the last week of April and early May producing most reports. Reports of either of these species much before the 25th of April are probably misidentified Hammond's. Keen birders readily recognize that a somewhat subdued whit heard during late April or early May is almost certainly Dusky rather than the later arriving Willow Flycatcher, whose similar call note is louder and snappier.
Pacific-slope Flycatcher -- Timing for this species is virtually identical to Hammond's Flycatcher. About the 15th of April is a consistent arrival date. By about the 20th of April, Pac-slopes can be found on territory along the heavily-wooded slopes at the margins of the Willamette Valley. Pac-slopes tend to stay high and inside the canopy and are best located by voice. Most birders recognize the loud "peer-weet" phrase that is part of their three-note song (last note is subtle and often unheard). The key to finding birds earlier during migration is to learn the high metallic tink note, which was taught to me many moons ago by David Fix. My earliest Pac-slope is 9 April. All of the pre-April 15 birds that I've encountered were detected by hearing the distinctive tink note.
Western Kingbird -- I generally expect to find my first kingbird of the season around the 20th of April. This season (Spring 2014), Western Kingbirds arrived early and in numbers with lots of reports before the 20th.
Cassin's Vireo -- In Eugene, you can almost bank on the first Cassin's Vireo appearing on Skinner Butte between the 1st and 3rd of April. I recall having my first of the year on the 3rd of April in several different years. I've never found one before April, but late March arrivals, at least in the southern Willamette Valley. are not particularly rare.
Warbling Vireo -- When I lived in Eugene, April 26th was the date that I expected Warbling Vireo to show up. My earliest ever was 16 April. For most of the Willamette Valley, the last week of April is when to expect this species. Wink Gross, who for more than a decade has tracked bird sightings seen/heard during his morning dog walks around Portland's Pittock Mansion, recently reported on Oregon Birders Online (OBOL) that 29 April is his mean arrival date for this species. By the first week May, small flocks of Warbling Vireos are normally evident at the popular Willamette Valley migrant traps.
Red-eyed Vireo -- This is a very late arriving bird in the Willamette Valley, rarely appearing at traditional nesting sites before the last few days of May.
House Wren -- This species normally starts showing up about the third week of April, right around the 20th is a good date. This year, I heard my first of the year at Cooper Mountain southwest of Portland on Easter Sunday (April 20th).
Hermit Thrush -- Appreciating the Hermit Thrush migration through western Oregon is a challenge because it is the default Catharus thrush here for most of the year. Small numbers winter in the western Oregon lowlands, but there is noticeable migratory push through western Oregon that occurs about mid-April or so. During nearly four hours of birding on Mt. Tabor 25 April 2014, we had at least 6 Hermit Thrushes. Birders anticipating the arrival of migrant Swainson's Thrushes often mistakenly identify Hermits as Swainson's. Generally speaking, any thrush seen in western Oregon before May 1st is likely a Hermit.
Swainson's Thrush -- Over the years I've been pretty long-winded on this topic. Mike Patterson, who has been birding in Oregon longer than I have, has been banding birds in Clatsop County on the northern Oregon coast for more than three decades. His Swainson's Thrush captures suggest that the second week of May is the normal arrival window, with the mean date for his first captures falling on 9 May (posted on OBOL). I recall seeing a Swainson's on the 3rd of May once and considered it to be 'early' at the time. Some reports from the last few days of April are credible, but most April reports are made casually by observers who perhaps don't realize that the expected Catharus during this period is Hermit Thrush.
Orange-crowned Warbler -- This is one of our two earliest arriving parulids. Truly migrant Orange-crowneds normally start showing up during the last 5-8 days of March. Birds seen prior to about the 20th of March should probably be considered overwintering. Small numbers of Orange-crowneds winter in western Oregon every year. Note that at least two and perhaps three subspecies of Orange-crowned Warblers migrate through Oregon in spring, so their passage is a bit bi-modal. The early arriving birds are generally males of the more southerly and westerly breeding subspecies O. c. lutescens. These birds are brighter green above and somewhat yellowish below, with the brightest birds occasionally being mistaken for female-type Yellow Warblers. Female lutescens, which are slightly duller olive, tend to dominate the flocks during the mid-April passage. Later in the season, usually about the last week of April or the first week of May, there is another wave of Orange-crowneds that shows up at the migrant traps (i.e. Skinner Butte and Mt. Tabor Park). These birds tend to be grayer on the head, duller olive-green overall and show very limited yellow below, with the yellowish undertail often being the most colorful part of the bird. This wave of birds is presumed to be of the boreal nesting subspecies O. c. celata, which breeds across boreal Canada and Alaska. Some of the birds in the later passage show characteristics consistent with the breeding population from the Rocky Mountains–O. c. orestera–but the in-the-field identification criteria for these birds are not clear cut.
Nashville Warbler -- The first northbound Nashvilles normally show up from 10-15 April, with numbers peaking in the Willamette Valley about the third to fourth week of April. Nashvilles nest at higher elevations and most are gone from the valley floor by the second week of May. In years when the weather is colder and wetter, they seem to linger in the lowlands later and in greater numbers. One or two Nashvilles are found during most winters in Oregon, so any bird seen prior to April is likely overwintering and not an early migrant.
MacGillivray's Warbler -- The first reports normally come about the 20th of April. I've had birds in the late teens of April in several years. This species is occasionally reported from the Rogue Valley in the early teens of April. This species is extremely rare during winter in Oregon, thus a bird before about 15 April is likely an early migrant. They are skulkers and seem less inclined than other warblers to sing while still migrating. However, they do have a fairly loud thick chip note, which once learned aids in detection.
Common Yellowthroat -- Among the warblers, only Orange-crowned arrives earlier. This species, which prefers wet grassy pastures, wetland edges, and riparian margins, seems to arrive on territory during the last few days of March and the first few days of April. Your first encounter of the season is almost guaranteed to be hearing the loud and distinctive "witchity witchity witchity" territorial song of a male. Off hand, I can't recall ever seeing my first Common Yellowthroat of the year without hearing it first.
Yellow Warbler -- This is one of latest arriving warblers in western Oregon. In the Willamette Valley, the first of the season often don't show up before at least the 25th of April and they are rarely conspicuous at migrant traps before the first week of May. During the big early to mid-April push of lutescens Orange-crowneds, extremely bright birds are sometimes reported as Yellows.
Yellow-rumped Warbler -- Although present throughout the year in western Oregon, there is a conspicuous April flight of this species. Most of the overwintering Yellow-rumpeds, particularly along the outer coast, are white-throated Myrtles, which nest far to the north of Oregon. Early in the migration period the mix of Myrtle and yellow-throated Audubon's Yellow-rumped Warblers is close to 50/50 split. The more northerly nesting Myrtles start to thin out considerably in late April and are almost entirely gone by mid-May. As these birds transition into gaudy alternate plumages, you'll see mostly Audubon's. Clearly migrant Audubon's, which are common nesters at higher elevations in the Cascades, start thinning out in the Willamette Valley by mid-May.
Black-throated Gray Warbler -- At Eugene, the first BTGs were almost always found by the 7th of April, often earlier. They aid in their own detection by singing during migration. They arrive a few days later farther north in the Willamette Valley, with the first Portland-area reports typically coming after the 10th of April.
Townsend's Warbler -- This species is uncommon in winter in the Willamette Valley, but there is noticeable migratory push starting about the 10 of April and lasting well into May. Although similar in many respects to the strident, buzzy song of Black-throated Gray Warbler, the song of Townsend's Warbler is more slurred and lazy. Townsend's, particularly in migration, sound like a drunk Black-throated Gray. On their breeding grounds they sound a bit more sober.
Hermit Warbler -- Usually appears at the Willamette Valley migrant traps around the 25th of April, sometimes a little earlier. Hermits occasionally winter in the Willamette Valley. Any bird found earlier than about the 15th of April is likely to have wintered nearby. Upon arrival, they seem to quickly move up slope to mid-elevation breeding sites. Skinner Butte, Mt. Tabor, and Pittock Mansion get just a few of these birds per spring, as they don't seem to linger in the lowlands.
Wilson's Warbler -- The 17th of April seems to be the typical date of first detection. I've had Wilson's as early as April 10th. Wilson's seem to go from absent to ubiquitous as fast or faster than any of western Oregon nesting passerines. One day there are none and a day later territorial males are singing in every direction.
Yellow-breasted Chat -- Chats arrive fairly late in western Oregon and they are rarely reported before early May. I can't say that I have much of a handle on the arrival date for this species. Their somewhat spotty distribution in nw. Oregon doesn't lend itself to consistent study.
Chipping Sparrow -- Although a few overwinter in the Willamette Valley, the first migrant Chipping Sparrows normally appear in the Willamette Valley about the first week of April.
Western Tanager -- When I think of W. Tanager arrival, April 25th readily comes to mind. Lo and behold I heard my first of 2014 on April 25th at Pittock Mansion.
Black-headed Grosbeak -- This is yet another species that seems to appear right around the 25th of April, sometimes a few days earlier. By the first few days of May you can expect to hear their song, which sounds like an American Robin on speed, in appropriate breeding habitats.
Lazuli Bunting -- The earliest birds seem to hit the Rogue Valley around the 20th of April, but they rarely appear around Eugene before the 25th of April and don't reach the Portland area until about the 1st of May. I heard what sounded like the buzzy call note of a Lazuli a few times at Mt. Tabor on 25 April 2014, which seemed a bit early. Ultimately, I think I may have been duped by a Lesser Goldfinch.
Bullock's Oriole -- Usually reaches Eugene by about the 27th of April and the Portland area by the first few days of May. Rarely numerous in breeding areas before the 10th of May.
Hopefully, this phenology and discussion provides answers to some of the common questions about spring migration. Below are some links to other spring migration phenologies for western Oregon: