Appearance

Adult Field Sparrow; Oklahoma, December.

Figure 4. Annual cycle of breeding, migration, and molt.

Molts And Plumages

Field Sparrows exhibit an unusual sequence of molts and plumages as well as unusual patterns of flight feather replacement. Essentially identical molting strategies have been documented recently for Bachman’s (Aimophila aestivalis) and Cassin’s Sparrows (A. cassinii; Willoughby 1986), and for various cardinaline finches and Yellow-breasted Chats (Icteria virens; Rohwer 1986, Young 1991, Thompson 1991a, b, 1995). By definition, the names of the molts and plumages described below reflect evolutionary homology. For a detailed explanation and discussion of how homologies (and therefore names) were determined see Thompson and Leu (1994). Colors follow Smithe (1975).

Hatchlings

Down on capital (head), dorsal (back), humeral, femoral, caudal, alar (secondary covert), and ventral (abdomen) tracts (Saunders 1956). Down has been described as mouse-gray (Dwight 1900), dark gray (Dawson and Evans 1957), light gray to dark gray (Wetherbee and Wetherbee 1961), gray (Saunders 1956), wood brown (Smithe 1975: color 25 [fawn]) anteriorly and vinaceous buff (Smithe 1975: color 219D [beige]) posteriorly (Wetherbee 1957). Lengths and numbers of down feathers on each feather tract quantified by Walkinshaw (1939).

Juvenal Plumage

Prejuvenal molt begins at about 2 d, probably completed by beginning of Presupplemental molt. Because Presupplemental molt (described below) begins at 16–18 d most previous descriptions of “Juvenal” plumage actually refer to Supplemental plumage (e.g., Brewster 1878, Dwight 1900, Forbush 1929).

Juvenal plumage “dull and … considerably more streaked” than any subsequent plumage; forehead and crown dull gray, tinged brown posteriorly; nape flat gray; slight streaking on crown and nape; back feathers are dull buffy with black shaft streaks; rump and upper tail coverts gray buff and unstreaked; rectrices brownish, outer two pairs edged whitish; remiges brownish and edged with whitish except for tertials (S7–S9) edged with pale rusty; lesser wing coverts dark gray edged with pale buff; median and greater coverts also tipped with buffy white forming two white wing bars. Lores gray; inconspicuous cream eye-ring; auriculars gray tinged with brown; postauriculars flat gray like nape; chin and throat whitish and unstreaked (contra Dwight 1900). Underparts largely whitish, but breast, flanks and undertail coverts (slightly) tinged with buff; breast, sides and flanks also streaked, often appearing as spots or flecks. No distinct red brown is visible anywhere in the plumage, the richest shades being those of the edges of the tertials (Sutton 1935: 29–31; color plate 7).

Supplemental Plumage

Presupplemental molt begins at 16–18 d (typically late Jun or early Jul in first broods), ends by late Aug (Sutton 1935), and involves the limited replacement of some to most back plumage anterior to the rump (Sutton 1935, Graber 1955, Willoughby 1991).

This feather replacement results in a much more rufous colored lower back, like Definitive Basic plumage.

Basic I Plumage

Prebasic I Molt mid-Aug through late Oct. Because of the early timing and limited extent of Presupplemental molt, most previous descriptions of “Postjuvenal” molt (e.g., Dwight 1900, Ridgway 1901, Forbush 1929, Willoughby 1989, 1991) actually have been of First Prebasic molt and not Presupplemental molt. All body plumage, including greater primary and secondary coverts, and tertials (S7–S9) are replaced. Most birds also replace all remiges and rectrices. However, in the case of incomplete primary or secondary molt, molt begins somewhere in the middle of the primaries and secondaries (e.g., P3 and S5, instead of P1 and S1, respectively), and always continues until the outermost primary (P9) and innermost secondary (S9) is replaced.

Basic I similar to Definitive Basic except that minimal streaking on the underside may persist in some individuals.

Definitive Alternate Plumage

Contrary to most authors who stated that no Prealternate molt occurs in this species (Dwight 1900, Pyle et al. 1987), a limited Prealternate molt does occur. In Maryland birds, feather replacement started in Feb, increased into Mar, stopped in Apr with migration, and resumed in May, continuing through Jun or Jul (Fig. 4). This molt replaces buffy or rufous tinged feathers of the face (auricular, loreal, and supercilary regions) and slightly buffy feathers of the throat with feathers that are grayer on the face and whiter on the throat (Chapman 1910, Willoughby 1989, 1991). Willoughby claims that during this period there were at least 4 replacements of feathers on the chin and 2 or more replacements of feathers in other regions (Willoughby 1989, 1991), and that individual feather follicles may grow as many as 6 generations of feathers during a single plumage cycle (year). Willoughby (1991) speculated that the continuous replacement might function to minimize Mallophaga infestation in that hard-to-reach region during the long breeding season of these species (see also Foster 1969a, b). While controversial, confirmation of this result would require revision of current dogma regarding sequences of molts and plumages.

Definitive Basic Plumage

Complete Definitive Prebasic molt early Aug–late Oct (Willoughby 1989, 1991). Begins with replacement of feathers on the face and throat, then on the crown, and about 1 wk later on the breast and back. Flight feather molt begins about 2 wk after onset of body molt, and finishes about 2 wk before completion of body molt. Secondary molt begins with S7–S9 (S8 followed by S7 and S9), followed in about 2 wk by S1–S6. Rectrices molt from the central pair outwards; the outermost pair of rectrices usually drops about 9–18 d after the central pair. Sequence of body molt is further described by Willoughby (1991). Molt lasts 9–11 wk in individuals (Willoughby 1991).

Crown, nape, and ear coverts amber to tawny with grayish crown stripe. Sides of head pale neutral gray with buff or rufous-tinged feathers. Buff to white eye-ring. Back and scapulars cinnamon rufous with black to buff streaks. Upper wing coverts darker near shaft; greater and median upper wing coverts tipped with white giving rise to 2 wing bands. Rump and upper tail coverts Sayal brown with little or no streaking. Throat, undersides, and under surface of wing pale to light neutral gray. Remiges mars brown; primaries edged light brown, secondaries more rufous. Rectrices Prout’s brown; outer ones narrowly edged with white (Dwight 1900, Roberts 1936, MC). Tallman (1984) discussed a partial albino.

Bare Parts

Bill And Gape

Hatchlings described as having bill gray near tomia, pinkish elsewhere, with mouth lining yellowish and pinkish near side (Walkinshaw 1939); bill pale yellow with deep pink mouth lining (Saunders 1956); and upper mandible gray on anterior half, rictal flanges light yellow, with bright red mouth lining (Wetherbee and Wetherbee 1961). In adults bill flesh color. Laughlin (1978) discussed a bird with a black bill.

Iris

Brown (Roberts 1936, MC).

Legs And Feet

Duller flesh to salmon color.