Often in birding, one comes across a familiar bird in an unfamiliar plumage. At first glance, a common bird in an aberrant or transitional plumage can fool even the experienced observer into thinking they are onto something really rare. In most cases, further study readily reveals that the bird is something expected rather than a first state record. I recently came across just such a bird. Among several pictures I took, I found the image below and immediately recognized that it might present a fun ID challenge. We'll give our readers a few days to try their hand at pinning a name on this bird before sharing its identity. Good Luck.

This bird was photographed in the U.S. (Lower 48) on 22 May 2010. Photo by Dave Irons

Last year at this time, BirdFellow published a wonderful article by Elizabeth J. Rosenthal, which chronicles the plight and precipitous decline of the Atlantic population of Red Knot (Calidris canutus rufa).  Her articles looks into the many factors, including over-harvest of horseshoe crabs, that have contributed to this decline. We encourage you to revisit (or visit for the first time) her piece entitled, "Help the Delmarva Ornithological Society Help the Red Knot" (published in this online journal on 28 April 2009).

In 2004 the Atlantic knot population was believed to number only about 13,000 birds, down from 90,000 in the 1980's. Recent conservation efforts, which have included a ban on horseshoe crab harvesting in neighboring New Jersey, seem to be making a difference as the 2009 census found 24,000 knots, the highest count since  2003. However, despite this modest recovery, scientists still consider the Atlantic population of Red Knots to be endangered.

Over the next week and a half birders all over Delaware will once again be working to see and hear as many bird species as possible in an effort to raise funds that will go towards the purchase of parcels of Delaware Bay shoreline that provide critical feeding stopovers for migrant Atlantic Red Knots. For the fourth consecutive year the Delmarva Ornithological Society (DOS) is sponsoring a bird-a-thon event. During the nine-day  Delaware Bird-A-Thon period, teams of birders may pick any day to go out and try to see as many bird species as they can during a 24-hour period. Similar to a walk-a-thon, birders collect pledges from friends, family, and co-workers for each species they tally. 

Perhaps no bird population on Earth has crashed as dramatically as the Atlantic subspecies of Red Knot. This adult knot, photographed at Mispillion Harbor, Delaware on 27 May 2007, sports coded green leg flags and a U.S. Fish and Wildlife Service silver leg band (right leg). Numbered and colored flags  allow biologists and researchers to relocate and identify individual birds from among the thousands of other knots migrating north along the Atlantic Coast each Spring. (Photo taken by Chris Bennett)

To date, three Delaware Bird-A-Thon events have collectively raised $120,000 for conservation. Those funds have already gone towards the purchase of 17 acres of prime shoreline on Delaware Bay, which are now being managed by the Prime Hook National Wildlife Refuge. In 2010, the DOS has formed a new partnership with the Delaware Dept. of Natural Resources and Environmental Control (DNREC), which will allow this year's bird-a-thon funds to be put towards the purchase of 52 additional acres of marsh at Mispillion Harbor. This marsh is vitally important to many species of migrant shorebirds and other wetland species.

We at BirdFellow echo the sentiments of prominent field guide author David Sibley who said, "What you can do to save the Red Knot: Support the Delaware Bird-A-Thon." Over the past year this journal has been visited by more than 15,000 birders from around the globe. If each of us were able to make a $10 contribution to this effort, we would raise more than the collective total raised by the first three Delaware Bird-A-Thons. To lend your support to this important effort, please visit www.dosbirds.org.

Unlike most members of the family Parulidae, Orange-crowned Warbler (Vermivora celata) is a species that is essentially devoid of field marks. It offers a study in the differences between greenish yellow and yellowish green, with some occasional olive and gray tossed in. It may or may not show wingbars, and may or may not show very diffuse streaking on the underparts. 

This Orange-crowned Warbler, photographed in low light on Skinner Butte in Eugene, Oregon 29 April 2010, presents an appearance consistent with the subspecies lutescens, which accounts for most of the Orange-crowned Warblers that pass through western Oregon each spring. Note the yellow eye arcs, uniform yellow underparts with diffuse dusky greenish streaking, and the general lack of gray tones in its plumage. Photo by Dave Irons

For all their drabness, I find Orange-crowned Warblers intriguing, in part because they are the first "migrant" warblers to reach Oregon each spring; Yellow-rumped Warblers winter here in abundance. Orange-crowneds are conspicuous migrants along the Pacific Coast of North America, second only to Yellow-rumped (among warbler species) in terms of the numbers one is likely encounter. From early April through early May they will generally be the most numerous species at many migrant traps, particularly on the cool overcast days that create fallouts.

This Orange-crowned Warbler, photographed in bright sun, also shows characteristics consistent with the lutescens subspecies. Note the fairly uniform yellow coloration below, yellow eye arcs, and lack of gray tones on the head. It does not show any obvious streaking below. Photo by Paul Rentz

What I find most interesting about this species is the variation it displays. The local breeding subspecies (V. c. lutescens) is the brightest of the three primary subspecies of Orange-crowned Warbler.  They can be almost lemon yellow below and rich leafy green above. As adults, they have yellow eye arcs that nearly connect to create a broken eyering and they often look a bit streaked below. Most of the Orange-crowneds that I see each spring are of this subspecies. They can be quite variable in appearance, with presumed females tending to look less yellow below. 

This lutescens was on Skinner Butte, Eugene, Oregon 29 April 2010. Its duller overall coloration suggests and lack of obvious orange tinge on the crown suggest that it is a female. Note that it is lacking in gray tones, has yellow eye arcs, and shows weak streaking below. Photo by Dave Irons

The duller and more northerly V. c. celata breeds across boreal Canada and Alaska and is presumed to be a low-density spring and fall migrant along the west coast. This subspecies displays a lot of gray tones and dull olive in its plumage. The yellow undertail coverts and vent often stand out as the brightest feathers on the bird. They seem to have less yellow (often creamy to off-white) eye arcs that form a near complete eyering. They tend to look unstreaked below. The bulk of this population is presumed to migrate east of the Rocky Mountains. The degree to which this subspecies migrates north along the Pacific Coast is at best poorly understood. Dunn and Garrett (1997) discuss celata as a fall migrant along the Pacific Coast, but do not describe its status as a spring migrant through that region.

A third subspecies (V. c. orestera) breeds in the Intermountain West northward along the Canadian Rockies to northern British Columbia. This subspecies is generally described as being more brightly colored than celata and tends to look more streaked below than the other two subspecies discussed here. Their most conspicuous feature is a very gray head that contrasts noticeably with the yellow underparts and green back. The have fairly bright yellow throats that are constrained and framed by the gray in the auriculars, which well down on the lower face. They also have whitish eye arcs. Fall immatures suggest a dull immature McGillivray's Warbler. They are somewhat regular fall migrants along the West Coast (Dunn and Garrett 1997) and I've seen a handful of spring migrant Orange-crowneds in western Oregon that have shown characteristics consistent with this subspecies. 

This Orange-crowned, photographed at the Chico Basin Ranch, Peublo Co., Colorado on 17 May 2008, is presumed to be of the orestera subspecies, based on range and the combination of uniform bright yellow underparts contrasting with a grayer head (creates a hooded look). It also shows whitish eye arcs. Photo by Larry Semo.

In Oregon, we get two distinct waves of migrant Orange-crowneds. The early birds, which arrive in late March and peak during the first two weeks of April, appear to be universally lutescens. They show no obvious gray and only minimal olive tones in their mostly bright yellowish-green plumage. Then, from late April until mid-May, we get a secondary wave of Orange-crowneds that are much duller overall. They often have distinctly gray heads and lots of gray tones on their backs. Their underparts are pale greenish yellow and usually look a bit washed out. The gray tones make them look mostly dull olive-green. In many cases their overall appearance looks intermediate between lutescens and photos of celata taken within their known range. Surely intergrades occur and it may be that many of the duller, grayer spring birds in western Oregon are intergrades. 

This bird, photographed on Skinner Butte in Eugene, Oregon 29 April 2010, is a classic example of the duller-colored Orange-crowned Warblers that pass through western Oregon during late April and early May. Its combination of paler underparts, significant gray on the head and upper back, and whitish eye arcs are suggestive of the subspecies celata, but this bird is greener than most of the presumed celata that I've seen. Photo by Dave Irons

My presumption, given the appearance of these birds and the timing of their passage, is that they are celata or at least celata/lutescens intergrades. However, to date there is no authoritative work on how to separate the three subspecies discussed here in the field. While I think that most of the duller Orange-crowned I see from late April on are probably celata, I have (as mentioned above) seen a few birds that were suggestive of orestera. 

I can't offer any definitive answers to the questions posed above, but I will continue be to take pictures of as many spring Orange-crowneds as I can in an effort to better quantify which subspecies are passing through Oregon in the Spring. A couple of long-time Oregon banders tell me that they have captured individuals that were keyed out as celata (Mike Patterson and Dennis Vroman pers. comm.). The photo below shows a presumed celata banded in Josephine Co. Oregon. 

This bird, photographed in Josephine Co., Oregon on 10 May 1992, was presumed to be a celata based on the overall dull plumage, pale underparts, extensive gray on head and nape, white eye arcs, and brighter yellow undertail (can't be seen in this image). Photo by Dennis Vroman

Hopefully, this discussion inspires others to take a closer look at the Orange-crowned Warblers and to photo-document celata-like birds along the West Coast. At this point, there are more questions than answers.