Significance for identification of species. This is probably the song-type that most birders depend upon for identification of Willow Flycatcher. It is diagnostic, but is not always given. Knowing about, and being able to distinguish, the similar sounds (see below) from Fitzbew is a good idea. That makes it possible to identify the species by song variety in many cases. Be ready for ALFL Pip-Weeoo.

Distinguishing features. The first two notes ( P1) can be resolved aurally, although occasionally they are connected, with the frequency trace rising above 7 kHz. (WIFL Whit seems derived from this phrase.) The long final phrase (P3) is typically preceded by two isolated clicks and one that is continuous with P3. These clicks no doubt contribute to the overall aural effect but are not likely to be resolved aurally by most listeners. In the western subspecies adastus and brewsteri the third click of P2 grades into the final sound, resulting in a rapid upsweep in pitch trend, as seen above; in other areas the third click is clearly separated from P3, which descends throughout its length. P3 changes form about one-third of the way through, indicative of a change in the rate and continuity of frequency modulation (periodic variation in pitch). The initial third is actually a series of very- closely-spaced "v-shaped" notes. This section of the phrase is low in amplitude in this example, but this is not typical. The final two-thirds of P3 is continuous, oscillating over a 2-kHz range every hundredth of a second. This modulation is slower than any modulation in the repertoire of the Alder Flycatcher. (In E. t. extimus this modulation is slower yet.) According to Stein (1963:24), Fitzbew is given with "two major throwbacks of the head."

Nomenclature: Many names have been applied to this sound, and some of them may be more onomatopoeic, but "Fitzbew" is one of the most firmly-established birdsong names in North America. It was also used in the 1960s and early 1970s to designate the as-yet-unnamed species that eventually became the Willow Flycatcher. Fizzbew is a distinct sound, not a variant of Fitzbew. Both are stereotyped and equally common, deserving equal billing in field guides. This has been known since 1963 ( Stein 1963).

Similar sounds. WIFL Fizzbew: Phrase 1 is a continuously-rising buzzy trill, mirroring Phrase 3. Phrase 2 usually has one isolated click instead of two. WIFL Zweeoo: like a brief Fizzbew but beginning with a series of clicks. Luckily, ALFL Zweeoo is less similar. ALFL Pip-Weeoo: This combination sounds surprisingly similar to Fitzbew. The Pip is continuous, not broken as is "Fitz." The leading part of Weeoo is continuous, not broken into two or three clicks. Despite these differences, and its briefer duration, Pip-Weeoo can cause trouble.

Combinations. Combined with Fizzbew and Creet in advertising song.

Significance for identification of species. This song-type is very similar in duration, bandwidth, and pitch-trend to Fitzbew, but being able to distinguish the two is useful for field identification. The use of two similar song-types by Willow Flycatcher distinguishes it from Alder Flycatcher. Also, Fizzbew is very similar to WIFL Zweeoo (Figure 4, Figure 5), so recognizing the latter certainly requires distinguishing Fizzbew from Fitzbew. Because of the rolling, ascending "Fizz" phrase, Fizzbew is more similar to ALFL Feebeeo than is Fitzbew. Be ready for a bird giving Fizzbew only, which is unlikely but possible.

Distinguishing Features. Field guides typically mention Fitzbew, then describe it as variable. That is not actually an accurate characterization of WIFL song-types. The three discrete song-types are each quite stereotyped, and not very variable at all. Fizzbew typically rises to a higher frequency (pitch) than Fitzbew. The "Bew" (P2 + P3) of Fizzbew is very similar to the "Bew" of Fitzbew and appears homologous to it, but P2 typically has one isolated click (plus one basted to P3) instead of two and the "v-shaped" notes in the first third of P3 are consistently farther apart than in the corresponding part of Fitzbew. As with Fitzbew, the onset of P3 differs between the northern western populations (adastus and brewsteri) and other populations (eastern traillii and campestris and southwestern extimus). P1 is a trill, an ascending series of very brief (5 msec), "v-shaped" notes separated by equivalent (6 msec) silent gaps. In contrast, the "burry", rising notes of the Alder Flycatcher are all continuous sounds with zigzag spectrographic traces, like the final, descending, part of "Bew."

Nomenclature: Some field guides do not name this sound, perhaps leading many birders to assume that the song (Fitzbew) of WIFL is more variable than the song (Feebeeo) of ALFL. Actually, Fitzbew and Feebeeo are equally stereotyped, but the song repertoire of WIFL is more diverse, with three song types rather than one.

Similar sounds. WIFL Fitzbew: Starts with two loud clicks, and P2 has two isolated clicks instead of one. WIFL Zweeoo: very similar, but noticeably shorter. The similarity is in the first, ascending phrase. In Fizzbew, the "Bew" is long and seems accented, while in Zweeoo the final phrase is short and insignificant. ALFL Feebeeo: Similar enough to confuse; rely on songtype variety in WIFL and ascending second phrase of Feebeeo. If you have very good temporal discrimination, listen for the click in the middle of Fizzbew, which is absent in ALFL Feebeeo.

Usage. With Fitzbew and Creet in advertising song.

Significance for identification of species. This brief sound is easily overlooked, but it is a full-fledged element of the advertising song of Willow Flycatcher. Hearing it along with Fitzbew and/or Fizzbew cinches the identification of Willow Flycatcher. It is not likely to be given repeatedly without Fitzbew or Fizzbew. It is quite similar in duration, pitch trend, and quality to ALFL Zweeoo, but Alder Flycatcher usually does not use its Zweeoo call in its singing performances. ALFL Zweeoo and WIFL Creet are easily distinguished with spectrograms.

Distinguishing features. Creet begins with a series of faint clicks (like ALFL Zweeoo), which are followed by brief "v- shaped" notes very similar to those in the opening "fizz" of Fizzbew. Then there is a silent gap. This is real, and is consistently present throughout the range of the Willow Flycatcher. The final part is a series of very brief "v-shaped" notes that may or may not be connected. According to Stein ( 1963:24), Creet is given with "a single throwback of the head."

Similar sounds. ALFL Zweeoo: Similar in duration and bandwidth, but continuous. WIFL Zweeoo: First phrase is continuous, without break seen above, and it has a second, descending, phrase. ALFL Feebeeo: "Fee" phrase is similar in duration and bandwidth but continuous, and the entire sound is much longer.

Combinations. With Fitzbew and Fizzbew in advertising song.

Significance for identification of species. This is the sound that is most likely to lead to the misidentification of a Willow Flycatcher as an Alder. This is a serious issue on the west coast, where Alders probably are rare spring migrants, but under-reported. When used, Zweeoo may be the only field mark available. It is used mostly for nest defense, but sometimes is given repetitively from a conspicuous perch, in the manner of advertising song. Its aural similarity to ALFL Feebeeo, combined with the repetition of the same call, which is reminiscent of singing by Alder Flycatcher, invite error. The Southwestern Willow Flycatcher's version of this call (not presented here) appears sufficiently distinctive to allow identification of that subspecies from this call alone.

Distinguishing features. The initial, ascending half of the call begins like a WIFL Creet (with faint clicks) and then resembles the "Fizz" of Fizzbew (with an ascending series of closely-spaced "V-shaped" notes). The absences of a silent gap and of more closely-packed notes at the end distinguish this half from Creet. The second half is nothing more than the call-type called Weeoo by Stein (1963) and Writ-tu by Sedgwick (2000). WIFL Weeoo is similar to ""Bew"", but is consistently different as follows: (1) The first part of P3 of "Bew" is absent in Weeoo. (2) The descending buzz in Weeoo covers the same frequency range as the final part of "Bew"," but each oscillation lasts 5-6 msec rather than 10 msec, i.e., it is modulated faster. ALFL Weeoo is similar to but distinguishable from WIFL Weeoo (Writ-tu). ALFL Zweeoo is continuous, and easily distinguished from this call.

Similar sounds. Fizzbew: Similar, but noticeably longer in duration then Zweeoo. In Fizzbew, the second phrase ("Bew") starts at a higher pitch than the end of the first phrase ("Fizz"); the second phrase of Zweeoo starts lower than the end of the ascending first phrase. ALFL Feebeeo: Also noticeably longer in duration. The "Fee" and "O" parts are not very different from the two parts of WIFL Zweeoo. It is the middle, "Bee" phrase that sets Feebeeo apart from WIFL Zweeoo. It makes the entire sound longer, and rises to a higher pitch than Zweeoo, giving Feebeeo a more ascending and higher sound. Creet: Creet is similar to first half of Zweeoo, but is broken rather than continuous. WIFL Weeoo and ALFL Weeoo: both resemble second half of this call (see above).

Usage. Often a stand-alone call (repeated, not mixed with other call- types). May be combined with Whit (which may be given by the mate), and occasionally with rare calls that are not stereotyped parts of the repertoire.

Significance for identification of species. This is the diagnostic sound by which most Alder Flycatchers are recognized. Although the repertoire of the species is large, this is by far the most commonly-heard sound. Being able to distinguish Feebeeo from WIFL Fizzbew and several calls of both species is essential. WIFL Fitzbew is so different that it should pose no problem.

Distinguishing features. The "Fee" part comprises a series of clicks, followed by a continuous note that oscillates in frequency as it ascends in pitch trend, followed by a chevron (ascending then descending frequency). The second major part ("Beeo") oscillates in frequency as pitch trend increases , does not oscillate as pitch trend drops very rapidly, and then oscillates again at the low terminal pitch. This is a single, continuous note. The ascending part is the "Bee" and the descending part is the "O." (See Kroodsma (1984).) The final descending click of Feebeeo is aurally unimportant (to humans); it is not the "O" of "Beeo." Note that amplitude increases throughout the "Fee," but increases and then decreases in "Beeo." The amplitude graph of WIFL Fizzbew is quite similar. Focusing on the "accent" of these sounds may not be helpful. (The amplitude spike in the rapidly descending part of "O" is widespread, but especially loud in this example.) According to Stein (1963:23), "This pattern is given with a single major throwback of the head, with a short jog at the bee."

Kaufman (1990) goes into more detail than other field-guide authors: "The song is strongly accented on the second syllable, which sounds both louder and higher pitched than the first." (Kaufman 1990:205) The pitch trend is clearly up through most of the song. I would conjecture that the sense of an "accent" comes from the sharp decline in frequency at the beginning of the "O" note.

Similar sounds. WIFL Fizzbew: about the same duration. Listen for the equal-duration ascending and descending pitch trends. Feebeeo rises steadily and then falls suddenly. WIFL Zweeoo is very similar. Its second half is similar in form to the "O" note of Feebeeo, and the two begin similarly. The main difference is that Feebeeo has the "Bee" note and WIFL Zweeoo does not. This gives Feebeeo a much longer ascending arm, and also its peak pitch is higher.

Usage. Usually not combined with other repertoire elements. Repeated monotonously in advertising song. Occasionally (Stein 1963, DAM pers. obs.) it is combined with Double-Peak in advertising song.

Distinguishing features and nomenclature. Stein (1963) gave the name "Churr" to strings of Pips that are punctuated with rough sounds, such as Weeoo. It seems better to follow Sedgwick (2000) and interpret these as combinations of trills and various rough sounds from the repertoire. In the Alder Flycatcher, some of these rough sounds are distinguishable from Zweeoo and Weeoo, and I refer to them as "Churr." The consistent feature of Churr is the evenly modulated buzz lasting around 100 msec and the absence of the high- arching initial sweep that characterizes Weeoo. ALFL Weeoo is quite stereotyped. Although Churr is more variable, the initial notes in the two examples above are stereotyped and seen throughout the geographic range of ALFL; e.g., spectrograms with shapes like these are presented by Stein (1963, Figure 6).

Similar sounds. WIFL Churr: Too rare to be characterized, but the initial notes in the two Churrs above appear to be restricted to ALFL. WIFL Weeoo is intermediate between these sounds and ALFL Weeoo.

Usage. With Pip and Trill, the entire indeterminate combination called "Churr" by Stein.

Distinguishing features. Trill is a series of Pip-like notes that are shorter and often lower than individual Pips. They are sometimes combined with Churr notes or other rough sounds.

Nomenclature. Stein (1963) used the name "Churr" for series that were characterized mainly by trills, but also include buzzy sounds such as Churr and Weeoo. With regard to the Willow Flycatcher, Sedgwick (2000) proposed the name "Trill" for series of Pip-like notes and referred to the sounds I call WIFL "Weeoo" ( Stein 1963) as "Writ-tu." I follow Sedgwick in using the name "Trill" for series of Pip-like notes in both species. I continue the usage of "Churr," but limit its application to the buzzy, frequency-modulated sounds presented by Stein (1963) in his Figure 6.

Similar sounds. WIFL Trill is indistinguishable. Similar-sounding trills are given by Gray and Hammond's Flycatchers.

Usage. Often with Weeoo or Churr (q.v.)

Significance for identification of species. Most field guides state that the call note of ALFL is "pip" and that of WIFL is "whit," and at least imply that these call notes are diagnostic. WIFL Whit definitively rules out Alder Flycatcher, but the reverse is not true for this sound, because WIFL has the very similar Whup. Although the two differ quantitatively, on the sparse evidence that is available, it would take a hard-to-assemble large sample of WIFL Whups to provide the backing for identifying an out-of-range ALFL on Pip alone. Fortunately, almost all other sounds of ALFL are diagnostic.

Distinguishing features. Symmetrical rising and falling arms. Higher and briefer than WIFL Whup.

Similar sounds. WIFL Whup (=Pip): Usually shorter in duration and lower in frequency, about 1 kHz in example shown here. Also, even the most Pip-like examples of the quite variable WIFL Whup tend to display the asymmetric pitch trend. Pip of Hammond's Flycatcher is quite similar. The ranges of Alder and Hammond's Flycatchers overlap extensively in Alaska.

Usage. Commonly with Weeoo, yielding a sound that has been likened to WIFL Fitzbew (Stein 1963). Interposed in Trills, which are essentially strings of shortened Pips.

Distinguishing features. Double-Peak is essentially two Pips basted together, or perhaps a Pip and a Pip-like combining form that is the initial feature of ALFL Weeoo. The first peak is typically about 45 milliseconds in duration, like ALFL Pip; the second peak is typically twice that duration, like the single peak at the beginning of ALFL Weeoo. Variation among individuals is substantial, and some individuals may be distinguishable by ear.

Nomenclature. The name "Double-Peak" was coined by Stein (1963). While spectrographically descriptive, it is inconsistent with the wide use of onomatopoeia in sound-names. It is based on spectrographic pitch trend. In as much as pitch trend is audible in this call-type, the name is a satisfactory descriptor.

Similar sounds. WIFL Double-Peak: Lower in pitch, but otherwise similar, and rare, whereas ALFL Double-Peak is used commonly, and sometimes used for singing (see below). In the two examples I've seen, WIFL Double-Peak begins at the top of the first peak, which should be audible in the field.

Usage. Frequently combined with Weeoo and Churr into a stereotyped combination that has been recorded independently by three recordists in Maine. With Churr in North Carolina (pers. obs.). It is also combined with Feebeeo in bouts of singing (Stein 1963, McCallum, pers. obs.).

Significance for identification of species. A rarely-heard sound from Willow Flycatchers, but the homologue is commonly used by Alder Flycatchers. For auditors familiar with the Alder Flycatcher, this sound may be misleading or confusing. Those not familiar with the sister species are also likely to be confused, because they likely have never heard this sound. I have never heard it in the wild. I know of two recordings, one from BC, presented here courtesy of Andrew Rush, and one from the Southwestern Willow Flycatcher. This WIFL call- type is not presented in any published sound collection that I know of, but it was mentioned by Stein (1963) and is represented on a training CD for Southwestern Willow Flycatcher workers provided by Mark Sogge of the USGS.

Distinguishing features. Essentially two Whups basted together. The first Whup may be incomplete, often starting, in the two examples I have seen (one from Southwestern Willow Flycatcher, E. t. extimus, one from British Columbia and hence probably brewsteri), near the peak. Note the presence here of a very loud harmonic, which is not obvious in the example of ALFL Double-Peak. ALFL Double-Peaks often do not have loud harmonics. Considering that harmonics in bird vocalizations have to be "intentionally" filtered out, the absence of a harmonic in ALFL may be an evolved isolating mechanism.

Similar sounds. ALFL Double-Peak: Higher, but other field marks should be sought to confirm identification. Hammond's Flycatcher has an infrequently- heard call, Whezee, which is spectrographically similar. As Hammond's and the Traill's complex are in different clades of Empidonax, these similarities are probably convergent rather than being homologous.

Usage. With Trill, Whup, and songs in the source tape for this sample.

Distinguishing features. Note differences between ALFL Pip and WIFL Pip, likewise for Weeoo. For distinguishing this combination from WIFL Fitzbew, focus on the Pip, which is more musical that the "Fitz" phrase.

Similar sounds. WIFL Fitzbew, WIFL Whit-Weeoo.