Plumbeous Vireo: The Range of Misconception

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While this dull Cassin's Vireo, photographed in Wasco County, Oregon on 2 June 2013, appears to show the slightest olive tones in its plumage in this image, seeing any greenish or yellowish coloration in the field was quite difficult. (Photo by Dave Irons)

Since the Solitary Vireo was split into three species (Blue-headed, Cassin's and Plumbeous Vireos), birders have struggled to separate these taxa when any one of them is reported outside of its normal range. In the Fall, separating putative Blue-headed Vireos on the West Coast is complicated by the fact that freshly-molted Cassin's Vireos are nearly as bright, colorful, and contrasting in plumage (Heindel 1996). Similarly, a suspected Cassin's Vireo found east of the Rocky Mountains must first be proven not to be a Blue-headed. 

Vireos sport their brightest and most contrasting appearance in the Fall after going through their only molt cycle of the year. Like other vireos, Cassin's Vireos seen during Spring and Summer can be quite dull and virtually colorless. The contrast and color one sees in the Fall are lost to feather wear and fading. During this season, it's hard to imagine how a Cassin's might be confused with a Blue-headed, but Plumbeous...that's another story. 

One of the by-products of any species split is a predictable surge in reports of the new species from locales where the former subspecies was either never, or rarely recorded. Trying to get a handle on the actual status and distribution of the new taxon can be a challenge because the first wave of such sightings comes before field guides catch up and authoritative ID articles are published. As we rush to fill the blank spots on the new scorecard, we do so without the help of well-vetted resources. Most birders don't concern themselves with trying to recognize subspecies, but once one is elevated to full species status and becomes available for us to tick off, the sense of urgency to do so ratchets up. 

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The bird in the images above and below is a Plumbeous Vireo that was photographed near San Jose del Cabo, Baja California Sur, Mexico on 8 January 2009. It strikes me as having stronger contrast at margins of the throat and seems heavier-billed and longer-tailed when compared to Cassin's Vireo. (Photos by Dave Irons)

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The breeding range of Plumbeous Vireo spans most of the Great Basin–Nevada, s. Idaho, Utah, w. Wyoming, n. and e. Arizona, and much of New Mexico (Goguen and Curson 2012). The northernmost breeding records are from Montana and to the south the breeding range extends into Mexico along the Sierra Madre (Goguen and Curson 2012). Although some presume that this species breeds in Oregon, there is no clear evidence for this being the case. 

Prior to 1997, when Plumbeous Vireo attained full species status, there were but a handful of colloquial and published "Plumbeous" Solitary Vireo records from Oregon. Most were not fully documented. Additionally, no specimen taken in Oregon has ever been assigned to this form. However, with the anticipation and eventual assignment of full species status the occasional claims of a Plumbeous Vireo, which formerly came every few years or so, have mushroomed into multiple reports per year.

Most of Oregon's reports of Plumbeous Vireos have fallen late May to early June. The majority of such sightings coming from desert oases/migrant traps in the southeastern corner of the state, where visiting birders arrive primed and ready to find vagrants. Note that this section of Oregon is sparsely populated and only a handful of active birders live in this subregion. I'm not quite sure how, or why it happened, but in the wake of the species split the Oregon birding community quickly came to accept that Plumbeous Vireo should be expected in southeastern Oregon at this time of year and that it probably breeds semi-regularly in this corner of the state. The evidence supporting either of these notions is at best, scant. There are but seven reports of Plumbeous Vireos that have been accepted by the Oregon Bird Records Committee (OBRC). Four of these are single-observer sight records and only two of the seven accepted records are supported by photos.  

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Here's another angle showing the June 2013 Wasco County bird (same as pictured at the top). When this bird was inside the canopy and backlit, it looked entirely gray. In this image, there appears to be the slightest tinge of green on the flanks just below the upper wing bar, otherwise it is gray and white. (Photo by Dave Irons). 

The species account in Birds of Oregon: A General Reference (BOGR) may have contributed to the misunderstanding of Plumbeous Vireo's status in Oregon (Nehls 2003). It starts by stating that the status of this species is "poorly understood." Then, there is a cautionary note about identification, which references Matt Heindel's excellent ID article published in Birding (Heindel 1996). It further points out that there are no Oregon specimens. Following these caveats, there is a roster of 11 cited records, including a putative nest found along Kelly Creek in southern Lake County in 1996. Apparently, the nest site was logged shortly after this discovery, thus no further documentation or photos were obtained. The account also offers that the species "has been reported in Harney County every spring since 1992." It's hard to read this account and not come away believing that the regular occurrence of Plumbeous Vireo in Oregon is well established. Many of the reports listed in BOGR (Nehls 2003) were never submitted to the OBRC and of those that were, two were not accepted. 

The issue with over-reporting of Plumbeous Vireos is not confined to Oregon. In California, ballooning spring reports of this new species from that state's coast and desert oases have also raised questions (Paul Lehman pers. comm.). According to Lehman and others, Plumbeous Vireos are still "scarce-to-rare" during Spring even in Southern California, despite an apparent increase in the numbers found there during fall and winter. Away from Southern California (Los Angeles south) Plumbeous Vireos are casual visitors at any season. Long-time North American Birds regional editor Guy McCaskie is of the opinion that there are only a few "ironclad" spring records from Southern California and that all good records are from the desert, with coastal reports being suspect (Lehman pers. comm.). As they have been in Oregon, reports from California's desert outposts are often poorly documented, as many birders believe that a spectacled vireo seen in desert/Great Basin habitats is by default a Plumbeous. From Oregon, Alan Contreras points out that northbound Cassin's Vireos continue to trickle through Harney County oases into early June, even though this species is not thought to breed in Harney County, or neighboring Malheur County to the east.  

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On 30 May 2010, three other experienced observers and I chased this bird around the oasis at Fields, Harney County, Oregon for nearly a half an hour. Until I captured this flight shot, which clearly shows a greenish wash along the flanks, we were convinced that the bird had no greens or yellows in its plumage. It spent most of its time in the shade and only showed tinges of green and yellow when it came out into direct sunlight. Even then it was a challenge to see these colors. (Photo by Dave Irons)

When seemingly credible sources repeat the same thing with enough frequency, claims that lack hard supporting evidence gain traction and start to become accepted 'fact.' Political parties are experts at this sort of manipulation of reality, often swaying public opinion with the repetition of half-truths, or murky data.

The birding world is not immune to being influenced by apparent critical mass. Unlike the manipulation that occurs in the political arena, birders tend to unknowingly perpetuate fallacies. When visiting sites where vagrant birds are found regularly, or birding a locale where a desired species is "expected," it can be a challenge to avoid the pitfalls that accompany expectation. Objectivity and healthy skepticism are too often replaced by an excited mind that is ripe for being duped. It's not hard for us to shoehorn the first plausible candidate into a species that we are hoping to see. It becomes easy to overlook what one subconsciously doesn’t ‘want’ to notice and see only those aspects of the bird that seem to best fit the species that one hopes to add to their list. If you’ve been birding for any length of time, you’ve probably stepped into this pothole a time or two.  

When birding desert migrant traps in southeastern Oregon–where Cassin's Vireos are low density spring migrants–the sight of an apparently dull and colorless spectacled vireo gets the blood pumping. If the bird stays inside the canopy and out of direct sunlight (typical for this species group), it's not going to be difficult to convince yourself that you aren't seeing yellows and greens in the plumage, because you probably aren't. Even knowing how dull Cassin's can be in the spring, I have twice been fooled into thinking that I might be looking at a Plumbeous in Oregon, only to have my camera or exposure to direct sunlight reveal color that I wasn't seeing when the bird was in the shade. Even in good light, the subtle colors of a spring Cassin's come and go with changes of angle. 

At this point, the actual status of Plumbeous Vireo in Oregon remains a mystery, in part because our birding community has applied little rigor to the examination of reports of this species. Acceptance of a presumed status is based almost entirely on a set of unreviewed or undocumented reports, hence there is a prevailing notion that reports of this species don’t require thorough documentation. I contend that we should start from ground zero and start treating Plumbeous Vireo as though this species is extremely rare in Oregon, which it may well be. Only then, will we be able to get a handle on their actual status. Getting that genie back into the bottle is easier said than done. 

Literature Cited:

Goguen, Christopher B. and David R. Curson 2012. Plumbeous Vireo (Vireo plumbeus), The Birds of North America Online (A. Poole, Ed.) Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell,edu/bna/species366 doi:10.2173/bna366

Heindel, M.T. 1996. Field identification of the Solitary Vireo complex. Birding 28:458-471. 

Nehls, H. B. 2003. Plumbeous Vireo. p. 401 in Birds of Oregon: A General Reference. D.B. Marshall, M.G. Hunter, and A.L. Contreras, Eds. Oregon State University Press, Corvallis, OR. 

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Pale Cassin’s in Harney County or elsewhere in Oregon almost always show very dull wingbars. As seen in the photos here, Plumbeous never have dull wingbars. Though I saw and was intrigued by the May 30th, 2010 vireo in Fields Oasis, the lack of strong wingbars was a good indication that it was not a Plumbeous. The throat contrast was also not extremely sharp. I think that I have photos of the bird somewhere.

Thanks, Dave, for this article!

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While I agree that Plumbeous Vireos seem to have consistently more conspicuous and crisp wingbars than Cassin’s Vireos–even those in fresh basic plumage (Fall)–I am reluctant to think that Plumbeous Vireos “never” have dull wingbars. I’ve seen some online images of putative Plumbeous that seemed to have weaker wingbars. I like to see more May-July birds to confirm this impression.

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Hi -

I chased a dull spectacled vireo around HQ at Malheur for over an hour last May. It never gave me a definitive look or photo opportunity.

Do we know normal arrival dates for birds breeding in the Rockies, say north of Colorado? That info might help screen Oregon reports.
Do we know details of habitat used by breeders in the northern parts ofv their known range, and where do those kinds of habitat exist in E. Oregon? In other words if someone were to search for summering, or breeding birds would it make more sense to search in Mahogany thickets? or in the pine forests north of Burns? or in the true firs around Anthony lakes? Or in the riparian cottonwoods along the Snake River?

Wayne

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Great topic to bring up with the approach of spring. I know you want to discuss if Plumbeous range into Oregon or not but in helping ID the Solitary complex, another point I would like to find out more about is the contrast between the line that is through the lores and the gray head. In Cassin’s it seems to be darker than the head. At least in Blue-headed it is supposed to be as dark as the gray in the head. I picked this up from Don Roberson’s website. http://creagrus.home.montereybay.com/sovi-id-comm.html. Not sure what the current thoughts are on the authors ideas.

SInce reading of this, the last few years I have looked at Cassin’s and the lore line has stood out against the color of the head. I looked at pics of Plumbeous on-line and have not been able to tell which way their lore line goes as to contrast. Hard to judge in photos, There was a very bright Cassin’s at Malheur a few springs ago, it was not a Blue-headed for other reasons, but even its lore line was darker that the head. I think this is something best worked out in the field, since photos can be rather misleading. It would be interesting to see what someone thinks who sees Plumbeous all the time or who can get access to a collection.

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To help with Wayne’s question: Here is the link for the Colorado Breeding Bird Atlas . Plumbeous Vireo is on pg 306. It says the males arrive in early May.

http://www.cobreedingbirdatlasii.org/New%20Home%20page/Colorado%20Breeding%20Bird%20Atlas%20I.pdf

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Dave,

I appreciate your concerns about the status of Plumbeous Vireo in Oregon and the other Pacific states. You bring up some good points and cause me to wonder about my past (presumed) experience with the species. I think that we can best get to the answer of what the status is of this species in Oregon only by hammering into as many peoples minds as possible what the field marks are for each in this triplet group of species (Blue-headed, Plumbeous, and Cassin’s Vireo—the solitary vireo superspeices complex). The standard that most people have who even think about such things seriously (which is a very small percentage of birders arguably) for Plumbeous is to look for an all gray vireo. A much smaller subset of that group understand the pitfalls of feather wear and molt that cause seasonal bias in misidentifying Plumbeous in Spring and Blue-headed Vireos in Fall. Then even a smaller supset understand additional field marks to look for like throat/hood contrast, feather edgings etc.. I know there have been good articles in Birding and perhaps elsewhere, but the more info and education that can get out there coupled with your call for photos and/or video and sound recordings will serve to help us answer this question more quickly.

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In response to Bob Archer’s point: Like you I read Don Roberson’s speculations about the usefulness of lore to hood contrast. I too have looked for this mark over recent years and it does seem to be pretty reliable. I don’t know how this carries over to Plumbeous, which always strikes me as a Blue-headed sans color. Imagine a Blue-headed in a black and white photo and you have a pretty close approximation of a Plumbeous.

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In response to David Bailey’s comment: Matt Heindel’s excellent treatment of the Solitary Vireo complex (Birding 1996) remains the best ID piece for these three species. His article was written and published in anticipation of the split the following year. Shawneen and I spent a night at Matt’s home in San Antonio a few years back. I queried him on this topic and have since exchanged some additional emails with him. Understandably, he has wearied of being the go-to guy on this topic and he lives in constant hope that someone will come along and offer an updated and improved version. Your assessment of the situation is quite accurate in my view. Few birders in Oregon or elsewhere at the margins of Plumbeous Vireo’s range fully appreciate how difficult it can be to separate these species and in some cases they are operating on a false set of notions about what should be expected.

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Here is a link to an article on id of the solitary vireo complex by Rich Stallcup with illustrations by Kieth Hanson: http://www.pointblue.org/observer/index.php?module=browse&browse_issue_num=148&browse_article_num=142&chooseIssue=1

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Dave,

I agree that either Plumbeous or Cassin’s could have either dull or strong wingbars. For spring migrants in Harney County, generally dull wing bars mean that it is probably not a Plumbeous. Strong wing bars does not necesarily mean Plumbeous, though.

Interesting about the lores – I’ll have to pay attention once the first Cassin’s Vireos of the year start showing up (believe it or not, probably a month or less!)

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