During spring and summer the woods are filled with the songs of migrating and breeding passerines. One of the most prominent and easy to recognize "song-types" in the U.S. is the "going up-coming down" phrases sung by several species of vireos. On those notes, we begin a multi-part series reviewing the identification and distribution of the species of this family (Vireonidae) that occur (or could potentially occur) in Louisiana. Because many species of vireos are superficially similar in appearance and voice, they can present a formidable identification challenge; this is especially true where species' distributions overlap, or for vagrants. Part I begins with the four "large, eye-lined" species (hereafter "LELV's"): Red-eyed, Black-whiskered, Yellow-green, and Yucatan vireos.
 
Status Red-eyed Vireo (Vireo olivaceus) is currently divided into two groups. A North American (olivaceus) group is widely distributed, breeding from se. Alaska across Canada (including sw. and ne. British Columbia, w.-central and sw. Mackenzie, n. Alberta, nw. and central Saskatchewan, n.-central Manitoba, central Ontario, New Brunswick, Prince Edward Island, Nova Scotia, and s. Newfoundland) and south into the U.S. to n. Oregon, n. Idaho, sw. and central Montana, Wyoming, e. Colorado, e. Oklahoma, s.-central and e. Texas, the central and e. Gulf Coast, and s. Florida. It is a relatively common species in bottomland hardwood and deciduous-coniferous forest habitats of our state. The first spring migrants arrive by mid-March, with birds already singing on territory shortly thereafter. Territorial males sing throughout the spring, summer, and into early fall. Spring migrants also sing, and, for this reason, it can be difficult to separate local breeders from northbound migrants. In the cheniers of the immediate coast (where Red-eyed is, at best, a scarce and local breeder) good numbers of spring migrants are regular into late May, with stragglers into early June. Fall migrants have been detected on the coast as early as 10 July; greatest numbers of fall migrants are present late August-mid September, with occasional stragglers occurring into early November. Red-eyed Vireo winters in n. South America. Remsen et. al (1998) accepts only one "early winter" record for Louisiana, a sight record from the Sabine Christmas Bird Count, which may pertain to a very late fall straggler. The paucity of late winter records is similar to the pattern shown by other Neotropical migrants that primarily winter in South America.
 
The South American (chivi) group occurs widely in South America from w. Ecuador, Columbia, and Guianas, south to SE Brazil, E Paraguay, and central Argentina. Some southern populations (up to nine subspecies recognized) are migratory. Most populations are very similar in appearance to Red-eyed (especially face pattern), but are generally more olive and yellow below (but lacking extensive yellow along the sides of Yellow-green Vireo) and have shorter, less pointed wings. There are no records of this group north of the South American range, though vagrants could be anticipated if austral migrants overshoot, as in the case of Fork-tailed Flycatcher. Detection would be difficult due to similarity with North American group.
 
Black-whiskered Vireo (V. altiloquus) is primarily a Caribbean species, occurring as a spring- summer resident from coastal central mainland Florida and the Florida Keys south through the Bahamas and most of the Greater Antilles (absent Grand Cayman), and as a year-round resident on Hispaniola, the Lesser Antilles, and islands off the north coast of Venezuela. At least a portion of the migratory populations winter in n. South America. The species is a rare to casual (mainly spring) migrant elsewhere in the West Indies, on the Caribbean coast of Central America, the U.S. Gulf Coast, s. Atlantic coast, and on Bermuda. In Louisiana (where it is a Review List species), there are approximately 50-60 records, all from on or near the coast (almost exclusively Cameron, Lafourche, Jefferson, and Plaquemines parishes) and mostly from the period mid April-early June; there are a few records from as early as mid March and as late as late August. A growing number of records for the se. coast (mainly Grand Isle) during June-August, including apparently territorial individuals and pairs, and individuals carrying food, suggests possible breeding there. Two subspecies have been collected in Louisiana: V. a. barbatulus (the "expected" breeding subspecies of Florida, the Bahamas, and Cuba) and V. a. altiloquus (breeds on Jamaica, Hispaniola, and Puerto Rico). Birders tracking down "Red-eyed type" vireo songs in coastal woods in spring and early summer should be prepared to look through many Red-eyed Vireos, but may eventually be rewarded when the songster turns out to be a Black-whiskered Vireo.
 
Yellow-green Vireo (Vireo flavoviridis) breeds from nw. Mexcio and extreme s. Texas south through Mexico and Central America, and winters in w. Amazonia. The species is a regular fall vagrant to California, and has also strayed (mainly in spring) to Arizona, New Mexico, w. Texas, the Gulf Coast, Bermuda, Barbados, and Venezuela. There are only two well-documented Louisiana records, both from Cameron Parish: 2-3 May 1992 (singing male) and 3-7 July 1998 (2 singing); several other sight records are pending review by the LBRC). Yellow-green Vireo is on the LBRC Review List.
 
Yucatan Vireo (Vireo magister) is a sedentary species with a restricted distribution, occurring on Grand Cayman Island and along the east coast of the Yucatan Peninsula south to Belize (and adjacent offshore islets south to off Honduras). Although the species is not known to be migratory, there is one record of a vagrant for the nearby Bolivar Peninsula, Galveston Co., Texas, 28 April-27 May 1984 (photo on Texas Bird Records Committee Website). So, if it happened once, it could happen again, and maybe Louisiana will be next.
 
Identification basics As a group, vireos are fairly consistent in overall appearance, making ID "as a vireo," relatively straightforward. The combination of size and a relatively thin, insectivore-type bill, which is hooked at the tip of the upper mandible, characterizes vireos and separates them from similarly sized and shaped warblers. Most vireos are fairly deliberate, "sluggish" foragers (compared to their more hyperactive warbler counterparts), gleaning insects, caterpillars, or small fruit from foliage, occasionally hanging, hovering, or sallying for less-cooperative food items. Most species have a rather somber plumage, and all species have blue-gray legs and feet. Vireos are quickly separated into two main groups, those with prominent wing bars and those without. General proportions (including bill size, relative length of wings and tail), face pattern, under parts coloration, behavior, and vocalizations are important aspects to vireo identification. Adults (sexes are alike) and immatures are very similar in overall appearance, and there is little seasonal variation, making identification less complex than in many other groups with multiple plumages for different ages, sexes, or seasons. Males are slightly larger than females, and immatures average slightly smaller than adults. These within-species size differences are not appreciable in the field. Identification criteria of this family are fairly well treated in the popular field guides. NGS 2nd and 3rd Editions probably offer the best "all-around" quick reference to the vireos. The new Sibley guide may have consistently better illustrations with better color representation, but innovations such as "percent differences" for bill size, etc., are, at best, only marginally useful. Kaufman's older Advanced Guide didn't tackle the LELV's, only addressing Warbling vs. Philadelphia vireos. Kaufman's new Focus Guide, along with the new Stokes' guides and the older Audubon Master Guide, offers "real photos," but these guides have the usual drawbacks associated with comparing photos of birds in different postures, lighting, adequate representation of plumages per species, etc. Side-by- side illustrations are almost always superior when trying to compare variation in characters such as bill size and shape.
 
LELV's lack prominent wingbars and are further characterized by being relatively large, and sharing a similar face pattern (grayish cap bordered by a dark line, light superciliary stripe, another dark stripe through the eye, and paler cheek; Fig. 1). The most prominent plumage feature, therefore, is the dark horizontal line through the eye (the "eyeline"), creating a "striped" face. The "striped" face is shared to a lesser degree by the smaller Philadelphia and Warbling vireos (Fig. 2). All LELV's (at least to some degree) have a relatively long bill, an olive-colored back that contrasts with a grayer crown and mostly white under parts (including chest) with varying amounts of yellow or olive wash on the sides, flanks, and under tail coverts. Philadelphia and Warbling vireos have a less well-defined "striped" face and proportionately smaller bills. The yellow chest of Philadelphia immediately eliminates all LELVs, as well as Warbling Vireo. Although some large eastern Warbling Vireos are almost as large-billed as some Red-eyed Vireos, they have very limited dark around the eye, which looking more "blank-faced" compared to the LELV's. Warbling Vireo also lacks the dark line bordering the cap of Red-eyed Vireo.
 
As the name suggests, Red-eyed Vireos (as well as Yellow-green and Black-whiskered vireos) have a red iris as adults; Yucatan Vireos have brown eyes. Juveniles of the "red-eyed" species start off with brown eyes, which gradually turn to red anytime from late summer into fall and early winter. Though many field guides report that iris color can be difficult to see, a red or brown iris is usually obvious under favorable viewing conditions.
 
Many identification errors will be the result of trying to force the presence, absence, or extent of a particular character on the wrong species. The LELV's are very similar in overall size, shape, and basic coloration; actual field marks are few. Structural characters can be useful, but they are also very subjective. Bill length and width is a good field character, but caution should be used because differences are subtle and some measurements overlap between species. Fortunately, presence or absence of combinations of a few diagnostic plumage characters will identify most individuals. Red-eyed Vireo is by far the most abundant and widespread species. So, nearly 100% of the LELV's that observers encounter in Louisiana during their lifetimes will be Red-eyeds. Thus, observers should take advantage of becoming thoroughly familiar with Red-eyed so that they are familiar with the full range of Red-eyed variation, and, thereby, become better prepared for that eventual "close encounter" with one of the other LELV's. Although Red-eyed Vireo is a common breeder here, territorial birds dwelling in the canopy of tall forest can be frustratingly difficult (literally, a pain-in-the-neck) to observe, especially because they often sing while sitting motionless and obscured by foliage. Better opportunities for close study can usually be had on the coast, where migrants can be plentiful and are forced to forage in shorter vegetation. And, of course, there is a better chance to find those "other" species on the coast.
 
Molt The Juvenal plumage is the first true plumage, acquired as young vireos replace their natal down. This plumage, which is held only for a few weeks during the nestling-fledgling period, generally resembles the adult-type plumages, but is duller, with more fragile, airy-appearing feathers that are somewhat more buff- toned. By the time fledglings are independent of their parents, most juvenal body feathers are in the process of being replaced via the First Pre-basic molt; this molt is incomplete, involving only the body plumage. Immatures in First Basic plumage look essentially like adults, except for very faint wing bars (but not easily confused with those species with prominent wing bars). The First Basic plumage is held until the following late summer when a complete molt into Definitive Basic plumage replaces all body and flight feathers. Because the Juvenal flight feathers are held for a full year before being replaced, first-year birds will have somewhat more worn-looking wings and tails in their first spring/summer.
 
Adults generally have only one complete molt (post-breeding) per year, although molt is not well understood in all species. This Pre-basic molt is initiated on the breeding grounds prior to fall migration, but it is unclear whether the molt is: 1) also completed on the breeding grounds; 2) is suspended and then completed upon arrival on the wintering grounds; or 3) is arrested after a partial or mostly complete molt and then augmented by a partial Pre-alternate molt on the wintering grounds prior to spring migration (see BNA, Pyle). There may also be individual or interspecific variation in the timing of molt, but this needs further study. Review of LSUMNS specimens of adult fall migrant Red-eyed Vireos (n = 13) does not seem to support to a (obvious) suspended/arrested molt; the plumage of all adult specimens appears fresh. Regardless of these potential complexities, southbound migrants (adults and immatures) are generally in "fresh" plumage. Vireos are their most "colorful" when in fresh plumage. By spring, the plumage begins to wear and fade; breeding birds in mid-summer are the most worn/drabbest in appearance. The greatest potential for confusion due to overall plumage pattern is generated by bright fall migrants that are more extensively washed with yellow below, or by first-year birds or breeders in mid-summer that are worn and may be drabber than anticipated.
 
Identification of large, "eye-lined" vireos Red-eyed Vireo (Vireo olivaceus)
 
This species is characterized by its blue-gray crown and light grayish-white supercilliary stripe, which is bordered above and below by a dark line. The line through the eye is prominent, being darkest in front of the eye (lores), but also extending behind the eye and gradually disappearing into the area above the cheek (see Fig. 3). Occasionally, the dark lores appear to drop down towards the malar area. Under certain lighting conditions, birds may appear to have dark "streaks" in the malar area (when none actually exist), thus suggesting a Black-whiskered Vireo. Don't jump to conclusions if you think you see "whiskers," look carefully at the sides of the throat to make sure that you are not being fooled by an optical illusion caused by the light (shadow) or the arrangement of the bird's throat feathers. In some cases missing or molting feathers can cause the illusion of a mustache mark; be especially cautious of individuals with wet plumage, which can cause a "part" between the feathers along the malar area. A relatively long-billed Red-eyed Vireo can further fuel the illusion of a Black-whiskered, but don't be fooled. The cheeks and sides of the neck are olive. The under parts, including the throat, are white. There is some olive blending into the white at the sides of the breast (at bend of the wing) and there can be a yellow suffusion to the under tail coverts and flanks; the yellow is most prominent on fresh fall individuals. Even the brightest birds will not show the extent of yellow present on the sides of Yellow-green Vireo (Fig. 4). The nape, back, and rump are olive and contrast with the blue-gray crown. The long wings are brown, with the primaries, secondaries, and their coverts edged olive. First Basic birds may show lighter edges to the secondary coverts giving a hint of a pale wing bar, but, in general, the wings are uniform (no prominent wing bars). The tail is also brown, with narrow olive outer edges to fresh feathers. Bill length is variable, with individuals ranging from relatively short- and dainty-billed with only a slight hook to the tip (suggesting eastern Warbling Vireo), to relatively long- and thick-billed with a prominent hook. [Despite the individual variation, there is no apparent geographical pattern in North American populations in bill size (or other size/plumage characters), and there are no recognized subspecies within the "northern" Red-eyed Vireo. Several closely related tropical vireos, including Yellow-green, have at one time or another been regarded as subspecies of Red-eyed.] The upper mandible (maxilla) is dark, the lower mandible pale. The iris is red in adults, initially brown in immatures, then gradually changing through brownish-red to red as the bird matures through its first fall and winter. Red-eyed is very similar in size and structure to Black-whiskered and Yellow-green vireos but, in Louisiana, there is probably equal potential for confusion with the relatively drab eastern Warbling Vireo, some of which can approach small Red-eyeds in bill and body size.
 
Voice. Most of the LELV's have a classic song, which is divided generally into two separate two to three note series. The first series rises, the second falls. An easy way to learn the "basic" vireo song is to compare the song to the following phrase "going up, coming down." Separating the similar songs of each species is more difficult and takes practice. The presence of internal note series or phrases (can be likened to "sighs"), in addition to the delivery and quality of the "going up, coming down" notes, can also be helpful in identification. Unlike the songs of "Solitary" and Yellow-throated vireos, Red-eyeds have more internal sighs or phrases. The delivery is also more rapid, without the pauses (a pause likened to a bird taking a long breath between series) in mid-song that are typical of, say, Yellow-throated Vireo. A good rendition of the Red-eyed song is in the BNA account introduction: "cherr-o-witt, cheree, sissy-awit, tee-oo." The cherr-o- witt equals "going up." "tee-oo" equals "going down. "Cheree" and "sissy-awit" represent the internal sighs or phrases. An individual Red-eyed can sing a variety of different variations on the basic song (and some degree of vocal mimicry has been reported), sometimes only the "going up, going down" portions or one or two internal notes are added. The calls of Red-eyed are variations of a nasal, "nearrh," and are often repeated in series. The calls are typically given in situations such as "scolding" at predators.
 
Black-whiskered Vireo (V. altiloquus)
 
This species is a slightly larger (though size overlaps), drabber version of the Red-eyed Vireo. The most prominent differentiating feature is the pair of dark "whiskers"- two lines of blackish-brown feathers extending from the base of the bill and bordering either side of the throat (Fig. 1). The whiskers, also commonly referred to as the malar stripes, mustache, or mustache marks, are relatively thin, generally averaging only 2-3 mm wide; width may vary to some degree as the bird changes its posture or the arrangement of these feathers. Contrary to some guides, this mark is not hard to see if you get decent looks at the bird (N=149, LSUMNS specimens). If there is question about whether whiskers are present, then, in all likelihood, they probably aren't (as discussed above in the Red-eyed account, but see also Yucatan Vireo account below). A note of caution: although, whiskers are prominent in Basic plumages, they may be indistinct or lacking in briefly held Juvenal Plumage. Four LSUMNS specimens molting from Juvenal, but primarily in First Basic Plumage had new dark whisker feathers that appeared to be replacing much paler versions. It is possible that during the First Pre-Basic Molt, missing or incoming sheathed whiskers may also be less distinct.
 
In addition to the dark whiskers, Black-whiskered Vireos have longer, narrower, and more strongly hooked bills than Red-eyeds (Fig. 3). But beware- some Red-eyeds can look relatively long- and thick-billed. The face pattern of Black-whiskered is duller than Red-eyed, because Black-whiskereds lack the prominent dark line bordering the dull gray cap and the light supercilliary stripe. The coloration of the crown and the supercilliary are relatively duller and less pronounced than on the average Red-eyed. The back has a more brownish suffusion to the olive and, therefore, there is less contrast between the crown and the back. The wings and tail are uniformly brown, edged with olive when fresh. The under parts are off-white (sometimes with a buffy cast); usually the throat and belly are the whitest. The sides are washed with olive, and, as for Red-eyed, there is usually a yellowish wash to the under tail coverts (most prominent in Basic plumages). The eye is red in adults, brown in juveniles. Differences between the two subspecies that have occurred in Louisiana (V. a. barbatulus, the "expected" breeding subspecies of Florida, the Bahamas, and Cuba; and V. a. altiloquus which breeds on Jamaica, Hispaniola, and Puerto Rico) are subtle.
 
Voice. Very similar to Red-eyed, and shares the "basic" vireo "going up, coming down." Separating the song from Red-eyed takes experience, but generally Black-whiskered is slower and somewhat "burrier." Calls are similar to Red-eyed.
 
Yellow-green Vireo (V. flavoviridis)
 
This species is essentially a more colorful version of a Red-eyed Vireo (Fig. 1), and, in the not too distant past, was even considered to be merely one of several tropical subspecies of the Red-eyed Vireo. The center of the throat, breast, and belly are white, and the sides of the throat and breast, the flanks, and the under tail coverts are bright olive-yellow. No Red-eyed ever shows as extensive bright yellow below (Fig. 4). As in Red-eyed, the cap is gray, and there is at least some hint of a darker line bordering the cap. The supercilliary is light gray and not as pronounced, becoming subtler or absent posterior of the eye. The face is primarily gray, with a hint of olive to the cheek, and contrasts with the olive-yellow that extends up the sides and meets the cheek. The back is generally a brighter green than in Red-eyed. The wings and tail are brown, broadly edged with yellowish-olive. The tail is predominately olive, the outer rectrices edged (seen from below) narrowly with yellow. The iris is red in adults, brown in juveniles. In general, the bill is longer and stouter than in Red-eyed, but similarly colored.
 
Voice. Similar to Red-eyed, sharing the "basic" LELV "going up, coming down," but generally faster, more "choppy," and "burry."
 
Yucatan Vireo (V. magister)
 
Yucatan Vireo most closely resembles Black-whiskered Vireo because of its drab appearance, but, of course, lacks the pronounced "whiskers." The supercilliary is drab white, more clearly white behind the eye, and, unlike Black-whiskered, does not fade posteriorly. The lores are extensively dark, forming a broad dark eyeline that then tapers behind the eye. The eyeline enhances the large, pale eyebrow. The face appears more striped than Black-whiskered. The cheeks of Yucatan are dull and blend into the white throat (the pale cheeks of Black-whiskered are outlined below by the dark whiskers). The under parts are dull white, subtly suffused with yellow on the flanks and under tail coverts. The upper parts are brownish-olive, the cap generally concolor with the back. The sides are extensively grayish-olive, giving the bird a more "dirty" appearance. The wings and tail are brown, edged olive. The bill is large, deep, and strongly hooked. Unlike the previous three species, the bill is mostly dark, with pale area restricted to the extreme base of the mandible (Fig. 1).
 
Voice. The song is reported as being similar to Black-whiskered Vireo (Raffaele et al. 1998). Calls presumably similar to other LELVs. Specimens at LSU Museum of Natural Science provided an invaluable resource. Distributional information is derived primarily from AOU Check-list of North American Birds, Seventh Edition. Additional data for obtained from the LSUMNS regional card or LBRC files and references listed below.
 
Cimprich, David A., F R. Moore, and M. P. Guilfoyle. 2000. Red-eyed Vireo (Vireo olivaceus). In The Birds of North America, No. 527 (A. Poole and F. Gill, eds. The Birds of North America, Inc., Philadelphia, PA.
Pyle, Peter. 1997. Identification Guide to North American Birds. Part I Columbidae to Ploceidae. Slate Creek Press. Bolinas, California.
Remsen, J. V., S. W. Cardiff, and D. L. Dittmann. 1996. Timing of migration and status of vireos (Vireonidae) in Louisiana. J. Field Ornithol. 67:119-140.
Remsen, J. V., S. W. Cardiff, and D. L. Dittmann. 1998. Status and Natural History of Birds of Louisiana 1: Vireos, J. Louis. Ornith 4: 59-102.
Raffaele, H., J. Wiley, O. Garrido, J. Raffaele. 1998. A guide to the birds of the West Indies. Princeton Univ. Press, Princeton, NJ.
 
Donna L. Dittmann & Steven W. Cardiff
435 Pecan Drive
St. Gabriel, LA 70776
 
Figures by Donna L. Dittmann: Fig. 1 || Fig. 2 || Fig. 3 || Fig. 4