The Challenge Looking at Empidonux by Bret Whitney & Kern Kaufman

Part IV: Acadian, Yellow-bellied, and Western Flycatchers (Empidonax virescens, E. fiviventr& and E. difSilh, respectively). (Empidonax virescens) (Plates 1 - 3) Voice The song is a loud, explosivepeef-see&or investigation. The tail is fairly long, and pee'-&@, or pee'-trup. The first syllable is tends to be uniformly wider than that of usually accented, but there sometimes seems other species when in a relaxed attitude. to be no accent on either syllable. The call is also rather loud but lacks tonal quality (very Plumage "flat") and is similar to the first syllable of The wing-bars and tertial4ghgs of adult the song: peellorpick.! No other Empidonax Acadians (except after wear, mid-tdate has a call like this. A onesyllabled call of summer) are welldefined, ranging in hue Yellow-bellied Flycatcher is clmst, being from white (second spring and older?) to about the same pitch and with a similar buffy-white (first spring?) in spring, and piercing quality, but ako with a falling, buffy-whiteto rich buff in fall. All juveniles, more "musical" inflection. and perhaps all adults after the post-nuptial molt (which is usually completed before the Structure leave the U.S.), have buffy wing-bars. Acadian is a large, long-winged Empid Adult Acadians in spring and fall typically with a lot of bill and tail. The bill averages show a neat whitish or yellowish-white eye- the broadest basally of any species, and also ring of uniform thickness, or thickness averages longest (but see Similar Species). slightly concentrated around the posterior The lower mandible is virtually always edge. In some individuals (a somewhat entirely pinkish-yellow or yellow but rarely higher percentage of worn summer birds), has a small dusky tip. the eye-ring is essentially lacking. Like Least The primary extension of Acadian averages Flycatcher, Amdian is characteristically quite the longest of all Empids, with a sabre-like uniform from crown to nunp, showing curve on the folded wing, long and straight essentially no contrasts in the upperparts or on the drooped wing. In fact, the wing may head. Aside fiom Yellow-bellied and Western be so long as to make the tail appear Flycatchers, Acadian shows brighter green proportionally rather short. The length of in the upperparts than does any other the primary extension on a short-winged Empidona species. This green is perhaps Acadian can be overlapped by those of best seen in the face and malar region. The ' Alder and Willow, and can rarely be green of the head and malar region, from matched even by Least, according to where it borders the sides of the whitish specimen measurements obtained by K. V. throat, runs posteriorly to the sides of the Rosenberg! The extent to which the primary breast, where it takes on a darker olive hue. extension might vary during molts needs This olive in the sides of the breast usually

Volume XVIII, Number 6 Plate 1: Acadian Flycatcher (E. virescens). Note the Plate2 Acadian Flycatcher (E. virescens).A very long primary extension, and drooped wing. This viewing angle and lighting aspect on the showm D individual appears to have a small dusky tip to the Plate I. Long wings evident, and a hint of green in k lower mandible. Fresh spring plumage shows a typical face and sides of upper breast is visible even st tLk even, yellowish-white eye-ring, and whitish wing-bars distance, imparting a rather weak facdthroat m and edges to the tertials. Plumage generally suffused Note that the tail, which would normally hang so& with a delicate greenish hue, uniformly through upper- lower, is propped up by a branch. Photo by Onik Aria parts and paling on to face and sides of upper breast. The throat and belly might be said toshow a very pale yellowish tinge, but one can imagine how whitish the underparts will look after a month or two of wear. This individual was fluffed to keep warm on a cold mid- May morning at Point Peke National Park, Ontario. Photo by Onik Arian washes almost through the center to impart junction with structural and other plumage a faint olive breast-band. characters. Adult Acadians are often largely white or Juvenile Acadian Flycatchers posses a grayish-white below, especially individuals very distinctive plumage. The upperpam with weak breast-bands or worn summer are bright green, many of the crown, nape. birds. On fresh spring arrivals, the underparts and upper wingcovert feathers (lesser and may be seen to bear a very pale, delicate median) with conspicuous buff tips. The greenish wash as ephemeral as the new wing-bars and tertialdgings are rich buff. opening of the spring leaves. The majority of The throat usually shows a light yellow adult Acadian Flycatchers have a whitish wash. The underparts typically bear a fairly throat. Following the fall and spring molts, conspicuous greenish breast-band which is however, Acadian may show a pale yellow often washed with clear lemon yellow that or greenish wash on the throat. This ap- runs posteriorly to the undertail-coverts. parently wears to whitish within a month or The center of the belly, however, is often so, but could cause confusion with Yellow- white. Unfortunately, this beautiful plumage bellied Flycatcher if not considered in con- is largely molted out by early September.

BIRDING, December 1986 C= Plate 3: Acadian Flycatcher (E. ~irescem).Yote the Plate 4: Yellow-bellied Flycatcher (E /laviwnlris). very long primary extension and relaxed wing. Even in Although focus is so& this plate is good for a typical very subdued Lighting (in the rain). the neat yellowish- protile impression of Yellow-bellied Flycatcher (small, white eyering and whitish aiog-bars and tertial- with round head and proportionally short tail). Note edgings indicative of besh spring plumage are evident. the rather short primary exteasion, bold whitish eye Stronger apparent face/thrmt contrast on this bird (as ring (obsolete bottom edge on this individual), and compared to Plate 1) is perhaps owing to a somewhat blackish wing with whitish wing-bars (upper not as whiter throat and darker sides of upper breast. (Third white as lower) and tertialcdgings. This is as pale and week of April, at Corpus ChiJu Texas.) Photo by John "colorless" (above and below) as a spring Yellow- Awin bellied is likely to appear, although sunlight will bring out more green in the upperparts at least. This bird apparently had not completed its pre-nuptial molt. (Mid-May, in Austin, Texas.) Phm by B. Whitmy.

and is unlikely to be seen far from the width. But when excited (for example, when breeding area. patrolling territory or trying to impress a mate), Acadian can be a spritely little bird, Behavior wing- and tail-flicking with the best of them. Acadian seems to be a relatively lethargic bird, sitting still for longer than the other Molt Empids, and doing less wing- and tail- Acadian is the only "eastern" Empid in flicking. The tail is flicked now and then, but which the adults typically undergo a complete the wings are very seldom flicked except for molt (the pre-basic, or post-nuptial) in late the first couple of seconds after settling on a summer before they begin their southward perch. In a relaxed mood, Acadian seems to migration. This molt can be underway as hold the wings and tail "at ease" much of early as late July and can be completed by the time, allowing the long wing-tips to early September, although in some indivi- droop below the tail. The tail is characteris- duals it is later. Juveniles have a partial tically parallel-sided (no basal constriction), molt, replacing mostly the body plumage and allowed to expand to its full, relaxed (thus losing the distinctive buff tips on the

Volume XVIII, Number 6 crown, back, and perhaps some of the wing- Acadians showing neat, uniform eye-ings covert feathers), beginning about the time and others having virtually none. they become independent, and generally Plumage-points to keep in mind when completed by early September. Thus, the faced with an Acadian/''Traill'sW are th vast majority of Acadians seen in fall will be most adult Acadians are very whitish below in fresh plumage, with buff or burn-white (except soon after molts), while most juvenile wing-bars, and often a noticeable yellow "Traill's" are lemon-yellow on the belll;, wash on the belly. (See the precautionary appear noticeably green on the back (especi- notes in the Similar Species section con- ally in direct sunlight), and have bufFy wing cerning the effects of wear on late-summer bars. Through spring and summer, both adults.) Acadian and "Traill's" show whitish wing- Spring molts are partial (wing and tail bars, sometimes with a buff tinge, but in fa4 feathers retained) and take place on the strong buffy wing-bars are the norm for wintering-grounds. Acadians of all ages. Onlyjuvenile "Train's" have buff wing-bars at this season; the wing- SiSpecies bars of adults (which have not molted are Acadian Flycatcher is most similar to thin and dingy whitish, showing evidence of "Traill's" Flycatcher (Alder/Willow pair). the summer's wear. It is important to remain It can be readily separated from "Traill's" conscious of predictable age- and m&- by either the song or the call. The bill related plumage variation in looking at structures and lower mandibles are very Empidonax-it can work for you (or similar, but Acadian's lower mandible against you!). averages both broader throughout its length and longer than "Traill's". The length of the primary extension is a more reliable charac- Comments on Distribution and Migration ter. Acadian's is almost always longer and Like many breeding primarily more pointed, but can occasionally be in the southeastern U.S., Acadian Flycatcher approached by "Traill's". Short-winged is a fairly early spring migrant, and starts Acadians seem to be more common than breeding by late April in the south and mid- long-winged "Traill's". This is perhaps a May in the north (here it is helpful to result of incompleted wing growth on remember that Alder, Willow, and Yellow- molting, post-nuptial Acadians. bellied Flycatchers are considerably later The birds are also close plumage-wise. spring migrants, concentrating in the latter Acadian tends to show less contrast through half of May). South-bound birds begin the upperparts than does "Traill's", especially moving by late July, and the species has between the head and back. Additionally, largely departed the U.S. by early September. even lighting will reveal the upperparts of Acadian is relatively little-known as a Acadian to be a lighter green, not as olive or fall migrant; birds seem to vanish off the flat in hue as is typical of "Traill's", setting breeding-grounds in late summer. At least up a generally stronger back-tewing contrast some birds linger well beyond early Septem- on Acadian. If studied at close range in good ber, however, as evidenced by late Sep light, the clearer green in Acadian's face, tember/early October 1986 sightings in especially just where the face meets the side southern Louisiana during prolonged warm, of the throat in the malar region, is helpful in humid weather (K.V. Rosenberg, pers. separating from "Traill's", which never comm.) and the report of 11 Acadian shows anything brighter than olive in the Flycatchers on October 29 and of 3 on face and malar region. Acadian's generally November 3 at Lafitte N.P., Louisiana paler face contrasts less sharply with the (American Birds, Central Southern Region throat than is the case for "Traill's". Acadian's report, Vo1.40, No.1). As noted by American eye-ring covers the entire range of variation Bird regional editor Robert D. Purrington between Alder and Willow, with some these Lafitte N.P. records came on the heels

BIRDING, December 1986 of Hurricane Juan, which probably camed Acadian Flycatcher winters from the the birds back to the U.S. from points south. slope of Nicaragua (probably Acadian frequently "over-shoots" the also Belize, and perhaps extreme southern breeding-grounds on spring migration, which Gulf-slope ) south through Central probably accounts for most of the non- America to northern and western Colombia, breeding records (especially in May) for northern Venezuela, and western Ecuador southern Canada (where it breeds very (AOU Check-lbt, 1983). Preferred habitat locally) and the northeastern US. Acadian is humid lowland forest and tall secondgrowth is the only Empid likely to be encountered below about 2500 feet elevation. Acadian is in any numbers on the middle and upper a bird of the forest interior on the breeding- Texas coasts in spring, at least before about grounds as well as the wintering-grounds, the last week in May. Acadian is extremely generally perching from about 10 to 30 feet rare west of the Great Plains (only a couple above ground. of records).

Yellow-bellied Flycatcher (Empidonaxflaviventris) (Plates 4 - 10) voice falling inflection. The two are easily recog- nizable once compared and learned. The song is a rather low, hoarse che-bunk orje-bunk, usually lacking a stronger accent Structure on either syllable. The song is most similar to that of , but is easily Yellow-bellied Flycatcher is a small but separable once the two are compared and proportionally large-billed Empid, often learned. As regards the call, Yellow-bellied giving the impression of being slightly large- shows more variability than any other headed and short-tailed. The bill is large Empid. One common call is distinctive in for the size of the bird in that it is both being a plaintive, two-syllabled, upslurred fairly long, and broad basally. The lower whistle: pr-wehe, the quality of which is mandible is evidently always entirely orange reminiscent of that of the Eastern Wood- yellow, lacking a dusky tip. The primary Pewee (Contopup virenr), although obviously extension is generally short to moderate, but emanating from a much smaller bird. This is can be noticeably short on some females, often shortened to a whistledpreeeor wreee, and long on long-winged males. There with a rising inflection. This single-syllable appears to be a significant tendency for call is sometimes shortened further still, and undisturbed Yellow-bellied Flycatchers to delivered more emphatically, without the look round-headed, or less often, with a gentle rising inflection: peer!This version of slight peak above and behind the eye (a the call is most often heard on the wintering- "crested" or distinctly peaked appearance is grounds, and is sometimes delivered at the unusual). rate of more than one per second. Also given (mostly on the breeding-grounds) is a sharp, -age explosive piyu! or chid, with a curt, falling Among the "eastern" Empids, Yellow- inflection; this is the call most closely bellied is almost always identifiable by the approached by the call of Acadian Flycatcher. distinctly yellow throat and underparts. On This latter species' call, however, is a flat some spring migrants and many summer exclamation, lacking any tonal quality or birds, however, yellow in the underparts

Volume XVUI, Number 6 319 Plate 5: Yellow-bellied Flycatcher (E. jlovivenrrir). Plate 6: Yellow-bellied Flycatcher (E. flovivenrrir). Note moderate primary extension (compare with Acadian Note proportionally heavy bill with entirely orange- Flycatcher), and blackish wing with bold whitish wing- yellow mandible. The eye-ring is bold and full, but ban and tertial+ngs. The conspicuous eye-ring defmitely concentrated around the posterior edge. appears to be strongly concentratedaround the posterior weakest along the top edge. It may come as a revelatioc edge of the eye from this angle. Note uniformity of that many spring Yellow-bellied Flycatchers are thir upperparts and weak fadthroat contrast. Outer vane pale yellow through the underparts (photo may k of outer tail feather noticeably paler than rest of tail slightly over-expased as well). Same bird as in Plate 5. (looking at the "undisturbed" tail of this bird, I was able but different angle and lighting heighten apparent to see no pale outer vane!). This is a typical, spring facdthroat contrast. Pholo by B. Whimey. migrant Yellow-bellied. (Mid-May, in Austin, Texas.) Photo by 8. Wh&y.

(especially the posterior half) can be very rather dark, almost blackish, and contrasts weak, reduced to little more than a pale and sharply with the wing-bars and back. This rather unevenly distributed wash. Yellow- contrast is somewhat diminished in summer bellied usually shows some greenish4live and fall adults, and in juvenile plumage, in (with bright-yellow undertones on strongly which the wing-bars are buffier. Spring 1 hued birds) on the sides of the breast, adults have white or yellowish-white wing- extending posteriorly along the sides in bars, with the upper one (tips of median adults and down to the flanks in juveniles. wing-coverts) often showing a slightly This imparts a blurry or streaky, greenish- stronger yellowish tinge than the lower olive "vest" to juveniles. (greater wingaverts). The tertial-edgings The upperparts and face, even on worn are also white or yellowish-white, usually a adults, tend to be the brightest green of the bit whiter than the wing-bars. By fall migra- genus (north of Mexico), matched season- tion time, these feather tips are often worn to for-season only by some fresh spring Western mere dirty whitish vestiges of the bold spring Flycatchers, and in fall, by some freshly wing-bars and tertialdges. molted Acadians. The wing of Yellow- Juveniles are more boldly patterned below bellied, particularly on spring adults, is than are adults, showing more extensive

BIRDING, December 1986 Plate 7: Yellow-bellied Flycatcher (E. floviventrir). Plate 8: Yellow-bellied Flycatcher (E. floviventrir). Note theshort primary extension. The plumage is in an Note rather heavy bill with entirely orange-yellow early stage of wear, showing abraded edges to wing- lower mandible. Strong greens in the head and face bars and tertial-edgings, and some of the scapular and show little contrast with the yellow throat. This is a belly feathers. The eye-ring is neat and of uniform typical Yellow-bellied eye-ring; note slightly thicker thickness. This is a drab Yellow-bellied, but at this time posterior edge, just hinting at a "teardrop". This is a of year and as the plumage becomes increasingly worn juvenile (skull unossified) in fresh plumage. Many and faded, a drab appearance is to be expected (weak juveniles show stronger greenish breast-bands or "vests" color saturation and graininess of film in original than this. (Early September, in Austin, Texas).Photo by transparency is also contributing to the overall pale B. Whitmy. effect here). This bird was photographed in late June (Acadia National Park, Maine); imagine what another month or two ofwear will do to this plumage! Photo by Tom Crabtree. bright yellow from throat to belly, and the Most adults and juveniles show barely paler extensive greenish-olive "vest". The wing- outer vanes to the outer rectrices. bars vary from yellowish-white to distinctly buffy (tertialedgings paler whitish). The Behavior upperparts are rather bright olive, not as Yellow-bellied, like Least Flycatcher, is green as on adults in fresh plumage. an active bird, doing much wing- and tail- The typical eye-ring of Yellow-bellied flicking as it moves from perch to perch. The Flycatcher (all ages) in fresh plumage is tail is not typically held parallel-sided, being nearly uniformly thick and conspicuous, more constricted basally than at the tip. and is white or faintly yellowish-white. The eye-ring tends to be slightly heavier along Molt the posterior edge of the eye, but there is The autumn molt of adults (the pre-basic, considerable variation in the shape of the or post-nuptial) may sometimes begin on eye-ring. Some individuals show narrowed the breeding-grounds, but it usually occurs or missing sections, and a minority show after the fall migration, so fall adults generally almond-shaped eye-rings with a slight "tear- look worn and drab. Typically the fall molt drop" projection on the posterior edge. is incomplete, with many of the flight

Volume XVIII, Number 6 feathers being retained. A complete molt hand, wait to complete post-nuptial mdts (the pre-alternate, or pre-nuptial) occurs in on the wintering-grounds, and look drab late winter, so that birds seen in spring with variably abraded whitish wing-bars in migration are in uniformly fresh plumage fall migration. Juveniles have fresh buff (which is not to say that the birds appear wing-bars like Acadians, but structural and bright yellow in the underparts in spring other plumage characters used in combina- migration; as mentioned above, many are tion will usually serve to separate juveniles only washed lightly with yellow). Juveniles of these two species. undergo a partial molt (involving only body Only Western Flycatcher is truly similar plumage) on or near the breeding-grounds, to Yellow-bellied the year-round. Form before their southward migration. nately, the need to separate Yellow-bellied from Western will not come up very often, Similar Species because their normal ranges barely overlap. See "Similar Species" under Least Fly- But some possible records of one or the catcher (Birding, Vol. XVII, No. 6, "The other out-of-range have remained in limbo Empidonax Challenge, Part 11"). It is because of the difficulty of proving the worth mentioning that, season-for-season, identification. The bad news is that the two Yellow-bellied shows less contrast between birds are structurally inseparable in the field the face and throat than is the case for Least The good news is that their voices (both Flycatcher. songs and calls) are very different. Careful It is commonly believed that Acadian note (ideally, a tape-recording of even poor Flycatcher is very similar to Yellow-bellied. quality) should be made of any vocalization The voices (both songs and calls), however, heard from a bird of the Yellow-bellied/ are very different, and these two are ap Western type suspected out of range or preciably different structurally. Acadian is season. considerably larger than Yellow-bellied in Now for the rest of the story. Surely, two overall length, and Acadian's bill is longer, species with such different voices, the vast and broader basally. The primary extension populations of which experience virtually of Acadian is usually conspicuously longer no overlap at any time of year, can't look than that of even long-winged male Yellow- exactly the same. Right. Not exactly the bellied Flycatchers. Also, Acadian's tail is same (Excuse me, but does anyone have a longer and broader, especially basally. microscope that we can borrow?). So. Acadian's plumage is basically similar, thinking of the big picture, remembering the but never shows the distinctly yellow throat broad range of variation that we know is and underparts characteristic of Yellow- there to foul us up, we'll attempt to scrutinize bellied. Freshly molted Acadians, especially a few characters that, if considered in com- juveniles, have a bright yellow belly and bination, may eventually prove (when the even some yellow on the breast, but the bird finally calls, or retires to a quiet place in throat does not have more than a pale a museum after all) to be of some value in yellow wash. Additionally, Acadian has less separating Yellow-bellied and Western Fly- of an eye-ring than Yellow-bellied season- catchers in the field. for-season. Finally, it is important to note Yellow-bellied tends to be a contrastier differences in the timing of autumn molts for bird than Western, with a blacker wing these two species, and plumage differences (especially the greater coverts, tertials, and resulting from these differing schedules. bases of the flight-feathers) and whiter wing- Acadian Flycatchers (all ages) typically bars. The tertial-edgings in particular seem complete molts on the breeding-grounds (or to look whiter and thus more conspicu- at least before moving south of the U.S.), ous than the dirty-whitish or brownish- and are thus in fresh plumage on fall white tertialedges of Western. Yellow- migration, all showing buff wing-bars. Adult bellied generally shows stronger green hues Yellow-bellied Flycatchers, on the other in the upperparts and breast-band, these

BIRDING, December 1986 Phte 9: Yellow-bellied Flycatcher (E, jkvivem). Phte 10: Yellow-bellied Flycatcher (E. floviventrir). Note the rather short primary extension (especially as Note the rather long primary extension (TIUSwas a compared to Acadian Flycatcher). the eye-ring attracts 6lmm-wingchord female!). Note buff-white wing- attention immediately, being bold, complete, and just bars (especially upper), and white tertial-edgina The hinting at a "teardrop" around the posterior edge. eye* is very bold, forming an irregular projedion at Note the blackish wing with yellowish-white wing-bars posterior edge. The upperparts are uniform bright olive; and whiter tertial-edging% The upperparts are uniform there is little facelthroat contrast (view is so close, and rather green. This individual shows as conspicuous however, that light reflecting off a few throat feathers a pale outer vane to the outer tail feather as this species makes them look white). The bill has something dark ever shows. This juvenile (same bird as in Plate 8) has stuck to lower mandible (not a dusky tip). This juvenile palm wing-bars than the rich buffof some birds. (Early (skull unossified) in hhplumage was photographed September, in Austin, Texas.) Phby B. Whirney. in Hays County, Texas, on the rather late date of October 18. Photo by Greg Lasley. areas on Western tending toward duller condition in each of the plates of Western in greens and olive with a brownish tinge. The this article, and on the cover of "Pacific pale feathers on the leading edge of the wing Discovery" (publ. Calif. Academy Natural at the "wrist", occasionally visible on a bird Sciences; Vol. XXXV,No. 4, July-August facing the observer, are buffy-yellow on 1982). Yellow-bellied tends to have a more Western, light greenish-yellow on Yellow- uniformly distributed eye-ring, but there is w bellied (rarely visible, and difficult to judge also more variation (everything from missing if it is-not to be taken as a diagnostic chunks, sometimes on the top edge, to small character). The above points refer to adults "teardrops") than seems to be the case for q in fresh plumage. Western. The amount of variation in eye- Differences in eye-ring shape between ring shape for both species needs more Western and Yellow-bellied may provide a study. helpful clue. Western shows a significant tendency to have the eye-ring strongly Finally, observers who are very familiar narrowed or broken across the top edge of with both species may notice that Western the eye, and elongated and thickened to a tends to be more "crested", or peakaowned, "teardrop" point behind the eye. The than Yellow-bellied, and proportionally narrowed top edge is shown in its typical longer-tailed.

Volume XVIII, Number 6 All of the preceding discussion on sepa- Rockies and is rare anywhere in the US. rating Yellow-bellied and Western Fly-, after about the third week of October. catchers in the field is based upon tendencies Yellow-bellied is a boreal-forest break, for the general population of one or the usually nesting in bogs. The breeding range other to lean toward one side of the scale. spans the continent from northern British Some of the characters represent differences Columbia to Newfoundland, and there is an in degree, and most are subject to high isolated breeding population on Mt. Rogers, seasonal variability. The best general pro- western Virginia (A.O. ZI. Check-list 1983). cedure for attempting to make a Yellow- Yellow-bellied can be hard to see on the bellied/Western species identification is to breeding-grounds, as it generally keeps well listen for any vocalization and take detailed, within the dense vegetation of the coniferom objective notes on the plumage condition, bog. Males occasionally choose relatively eyering, wings, and plumage contrastdhues. exposed song perches, however, up to 30 feet above ground. Comments on Distribution and Mgration The winter range of Yellow-bellied Fly- Yellow-bellied Flycatcher arrives in the catcher extends from northeastern Mexico U.S. on spring migration by about the (perhaps as far north as Cielito, Tamaulipas) second week of May (sometimes earlier, on the Caribbean slope and eastern Oaxaca especially south), peaking as a migrant in on the Pacific slope, south to western late May. Yellow-bellied is 0b~e~edon (Chiriqui). There is one record migration less frequently than most Empids as far north on the Pacific slope as San primarily because of its retiring nature, Blas, Nayarit (G.H. Rosenberg and K.V. generally keeping to denser thickets and Rosenberg, tape-recorded and photographed). woodlands. Yellow-bellied also seems to Yellow-bellied is very rare as far south and call less often on migration (but frequently east as the Canal Zone, and there is one in the winter) than most other Empids and record from Cana, Darih (A. 0.ZI. Check- very seldom sings until near the breeding- list 1983). As yet, there is no report from grounds in spring. In fall, migration begins . Wintering-habitat is usually by late July, peaking over most of the humid second-growth and edge of taller eastern U.S. and southern Canada between forest, from near sea level to at least 4,500 the last week of August and the first half feet in the mountains of Chiriqui, Panama of September, with stragglers coming Within drier regions of the tropics (such through into early October. Yellow-bellied as southwestern Mexico), Yellow-bellied is extremely rare in migration west of the winters in creek bottoms and humid ravines, avoiding arid slopes and flats.

Western Flycatcher (Ernpidonax difJici1k) (Plates 11 - 13) Geographic Variation Ranges, the Cascades,and the Sierra Nevada Two major populations of Western Fly- The race insulicola, breeding on the Channel catcher occur north of Mexico. Although Islands off southern California, is considered the known differences between them are to be of the coastal type. Interior birds breed slight, it has been suggested (Johnson 1980) from southern Alberta south through the that they may represent two distinct species, Rocky Mountains into Mexico and west so field-observers should be aware of their through the isolated ranges of the Great existence. The two populations are referred Basin region. At their western limits, birds of to here as "coastal buds" (E. d duficil& and this form breed locally in the eastern two- E. d insulicola) and "interior birds" (E. d thirds of Oregon (west at least to Crater hellmynJ Coastal birds breed from south- Lake), in northeastern California (west to eastern Alaska south to Baja California; the Siskiyou Mountains, but not the Mt. theu eastern limits are marked by the Coast Shasta region, which is inhabited by birds of

BIRDING, December 1986