Willow Flycatcher

The Willow Flycatcher is the most pewee like Empidonax flycatcher and without vocal cues is indistinguishable from Alder Flycatcher. The typical song is a snappy FITZ-bew.
Formerly considered conspecific with the Alder, the 2 together were referred to as Traill’s Flycatcher until 1973, when they were recognized as separate species. Like most members of the genus Empidonax, this flycatcher is difficult to identify in the field without vocal, habitat and geographical reference. 
The Willow breeds from Maine to British Columbia and as far south as southern Arizona and southern California. It winters from southern Mexico to northern South America in habitats similar to those occupied on the breeding grounds.

Adult Male (spring/summer)

Dark olive-brownish head and face; inconspicuous thin white eye-ring; cap darker with slight crest. Chin and throat white; breast pale olive-brown; flanks pale yellow; belly grayish-white and undertail coverts pale yellow-white. Nape gray; back, rump and uppertail coverts olive-gray and tail darker olive-gray. Wing is gray with white feather edging and two wingbars. Lower mandible is yellow-orange. Legs and feet are black.

Adult Female (spring/summer)

Similar to adult male.

Juvenile

Browner above, yellower below and wingbars buff or yellowish-brown.

General:

One of the largest Empidonax flycatchers, with relatively flat forehead and distinct peak on rear crown; long, broad bill; moderate primary projection; and broad, straight-sided tail. Length: 13-17cm. Wing: 19-24cm. Weight: 11-16grams.

Behaviour:

The Willow Flycatcher is primarily an aerial forager, capturing most of its insect diet on the wing, but it may hover-glean extensively from leaf surfaces or occasionally take insects from the ground. Diet consists mainly of insects but may take small berries in the fall.

Habitat:

Breeds in moist, shrubby areas often with standing or running water. In the west it is primarily found in riparian thickets.

Information:

The Willow Flycatcher is a common migratory species and the most widely distributed North American Empidonax flycatcher. This species was given its name in 1831 by J.J Audubon for his friend Dr. Thomas Stewart Traill of Edinburgh. 
The nest is a firm thick-walled cup of plant fibers lined with plant down and cottony fibers, placed in an upright crotch of a shrub 2-6ft high. The clutch is 3-5 creamy white or buff dotted with dark irregular markings around the large end of the eggs.

Similar species:

Alder Flycatcher.

Conservation Status:

Listed as Least Concern. Overall populations appear to be declining. Southwestern subspecies is listed as Endangered, extirpated from much of its original range. Listed on the Audubon Watchlist. Because the Willow Flycatcher is restricted to river corridors (at least in the arid parts of the West), it is vulnerable to a variety of human activities that may alter or degrade such habitats; activities including river dewatering, channelization, overgrazing, dam construction, and urbanization.

Capture Rates:

Common in high numbers and a breeding bird at Colony Farm, Willow Flycatchers are present in the park from May through October. Capture rates peak however in August corresponding to juvenile dispersal. This flycatcher migrates south for the winter as indicated by zero capture rates from November through April.

Molt Summary:

PF: HY partial; PB: AHY complete-incomplete; PA SY incomplete, ASY partial-incomplete

Preformative molt apparently includes the body plumage but few if any wing covs.
1st PA is eccentric, with the outermost 5 – 10 pp, the innermost 3 – 9 ss, and the rects, but no pp covs replaced. A few middle ss (among s2 – s6) sometimes can be retained during the adult PB, which are replaced during the adult PA. Alder Flycatchers show flight feather replacement in Jan – Mar (variable), and both SYs and ASYs appear to replace most if not all flight feathers (including the pp covs in SYs?)

Much is not known on molting patterns.

Willow/Alder (Traill’s) Flycatchers from other Empidonax Flycatchers

A good way to start is to divide Empids in to 3 main groups:

• White throat, white belly and spotted crown – Traill’s (Willow/Alder) and Least
• Greyish throat, yellowy belly and narrow bill – Hammond’s and Dusky
• Yellow throat, yellow belly and greenish back – Western (Pacific-slope) (and Yellow-bellied!)

The only Empid where P6 in NOT emarginated

• Bill large and wide (huge mouth) with convex sides with all pale (or almost so) lower mandible.
• Lores pale on Alder – Willow without conspicuous pale lores
• Dorsal plumage greenish on Alder – greyer on Willow (use with caution)
• Eyering narrow white and even width on Alder – weak or absent on Willow (use with caution)
• Crown spots larger and more distinct on Alder – Willow less distinct (use with caution as both age and sex related e.g. larger crown spots especially in AHY male Alder)
• Alder whines in the hand – Willow doesn’t!

Note: Willow and Alder Flycatchers cannot reliably be separated in the hand so all of the above should be used with caution!

P6 NOT emarginated:

Primary tip spacing:

P8 longest by a small margin and then two large gaps (P7-P6 and P6-P5)

Willow Flycatchers in first alternate (A, B) and definitive alternate (C, D) plumages. In the birds in first alternate plumage, the juvenile primary coverts have been retained and are worn and brown, contrasting with the replaced greater coverts.

Variation in the extent of the preformative and prealternate molts of the Willow Flycatcher. The preformative molt can vary from partial (A) to incomplete with an eccentric pattern (B) to almost complete (C), although most to all primary coverts are retained juvenile feathers, allowing birds to be aged in spring and summer. The preformative molt is always more extensive than the first prealternate molt.

Frequency of replacement of the median coverts, greater coverts, and remiges during the preformative, first prealternate, and definitive prealternate molts of Willow Flycatcher by subspecies.

The innermost primaries (P1-P3) are retained juvenal feathers on this SY in July contrasting markedly with the replaced outer primaries and secondaries. Notice not only the thicker, darker rachises on the replaced feathers but also the difference in shape between the retained and replaced feathers, the retained feathers thinner and more tapered than the replaced ones.

A similar example is this SY also in July. The innermost primaries (P1 & P2), outermost secondary (S1) and outermost greater covert GC1 (red arrow) are retained juvenal feathers again contrasting markedly with the replaced outer primaries and inner secondaries. Notice again the thicker, darker rachises on the replaced feathers and the difference in shape and wear between the retained and replaced feathers, the retained feathers thinner, more tapered and worn than the replaced feathers.

Another example on this SY in June with innermost primaries (P1 & P2) retained juvenal feathers and a retained outer greater covert GC1 (red arrow) and carpal covert. Notice again the thicker, darker rachises on the replaced feathers and the difference in shape and wear between the retained and replaced feathers, the retained feathers thinner, more tapered and worn than the replaced feathers.

Notice also the thin, tapered and worn retained primary coverts in this example.

This second year (SY) in June is showing a pattern similar to ‘C’ in the above graphic of an almost complete preformative/prealternate molt with replaced lesser, median and greater coverts, carpal covert, two alula feathers (A1 & A2), several primary coverts and all 3 tertials (S7-S9) with only some primary coverts retained juvenile feathers.

The tail of the above SY in June is showing fresh, truncate replaced rectrices with little wear to the tips replaced during the preformative molt which could easily be mistaken for adult (AHY/ASY) feathers, illustrating the importance of understanding molt strategies by age and subspecies in Willow Flycatcher.

3 more examples of second year (SY) birds in June is showing similar eccentric molt patterns and 3 generations of feathers; retained juvenile, formative and first alternate.