Appearance

No studies of molts and plumages or significant data on sequence, timing, or extent of molts for Snail Kite. Therefore, not possible to determine with confidence sequence of molts and plumages in terms of Humphrey-Parkes terminology; thus, molts and plumages are described here chronologically as best as possible.

Natal Plumage

Down A, first of 2 downy plumages, short (±1.5 cm), coarse, and buffy with tawny to light brown (warm sepia) or brownish olive patches on central crown, along dorsal and caudal tracts, and on upper wing surfaces; edges of dark patches may be tinged with cinnamon; small elliptical dark brown to black mask through eyes. Assuming second downy plumage, Down B, is homologous to that of other accipitrids, it grows from a separate set of follicles than Down A (i.e., it does not replace Down A, contra Bent 1937). Down B longer, denser, and dark grayish-brown, much darker than Down A except for mask which stays same (Bent 1937, Beissinger 1988, PWS).

Juvenal Plumage

Remiges appear at 4–6 d, rectrices at 8–9 d; contour feathers first appear on scapulohumeral tract at 9–12 d, dorsal tract at 16–18 d, ventral tract at 18–21 d, and capital tract at 21–23 d. Plumage fully developed by 4 wk (Beissinger 1988).

Sexes alike (Beissinger 1988); however, Bent (1937) states that sexes can be distinguished by tails, which show same differences as in adults (i.e., underside of tail being browner and more restricted and subterminal light portion more extensive in females). Entire feathering shades of browns and cinnamon buffs. Overall coloring of individuals varies from dark to pale. Head rich buffs to yellowish brown with fine dark brown streaking on crown, chin, and throat area generally unmarked, heavy streaking and blotching on rear of crown and neck, and broad dark horizontal, often ill-defined, line to rear of eye generally connecting to darker area of hindneck. Upperparts mottled; upper three-quarters or so of individual feathers dark brown or black coming to obtuse point along feather shaft, feather tip tan to cinnamon. Underparts buffy tan to cinnamon with diffused dark streaking; dark brown streak along feather shaft with lighter margin that generally becomes lighter as it progresses toward edge of feather. Tail mostly dark with pale tip. Rectrices mostly black with basal portion clear white, terminal centimeter or so buffy grading from darker to lighter at tip. Upper- and lowertail-coverts white. Wing-coverts dark brown to black with broad tip of cinnamon buff. Primaries and secondaries mostly black with narrow russet tips (Friedmann 1950, Beissinger 1988, PWS), innermost primaries and secondaries show some barring on underside which is much less obvious on upper surface. Not known how long all or part of Juvenal plumage retained.

Basic Plumages

Little information from known-age individuals. Interim condition of feathering after Juvenal and preceding Definitive Basic. Bent (1937) states that Juvenal plumage worn through first winter is subject to much wear and fading, bright colors fading to pale buff or nearly white. However, cinnamon buff of Juvenal plumage has disappeared to some degree, having white superciliary line by 2 mo after learning to fly, possibly resulting from Prebasic I partial body molt rather than wear. Bent (1937) also states that second-year birds undergo an extensive molt in spring involving much of body plumage, wing-coverts, and tail (this may actually be Prebasic I [annual] molt). Based on captive birds, there appear to be 2 Pre-Definitive Basic plumages, each consisting of entire feathering and each retained 1 yr. Early Basics show more contrast than Juvenal plumage; light areas white or whitish, dark areas very dark, and heavy streaking sharply defined. Last Pre-Definitive stage, presumably Basic II (III?) in male, apparently differs from its predecessor, being dark brown (not slaty) above and below, upper- and lowertail-coverts and base of tail white, secondaries and tail broadly tipped buff, and thighs barred rufous. Before Definitive Basic feathering is acquired, there is apparently marked sexual dimorphism in plumage coloration. With majority of Snail Kites in Florida showing streaked feathering, it is evident that a Pre-definitive condition exists for considerable period (Beissinger 1988).

Definitive Basic Plumage

Definitive Basic molt complete (?), protracted; feathers gradually renewed during or soon after initial nesting (Bent 1937). Sequence of feather replacement unknown, except primaries replaced from innermost (P1) to outermost (P10) (Beissinger 1988).

Male. Feathering of head, neck, upperparts, and underparts blackish slaty, which on some individuals may appear darker on head. Base of tail and uppertail- and lowertail-coverts white, remainder black with narrow, light brownish-gray to white terminal band. Wings blackish slaty, with primaries and secondaries black. In younger males, wing-coverts tipped with muted browns. Entire plumage with chalky bloom (lost in museum skins). Base of feathers in occiput area whitish, visible when feathers are ruffled by wind, present in all plumages (Juvenal plumage to adult) (Friedmann 1950, Beissinger 1988, PWS).

Female. Overall dark brown with light markings about head and streaked underparts. Head partly dark brown with forehead, superciliary, cheek, chin, and throat white. Most of remainder of feathering variably buffy tans and heavily marked and streaked with muted dark browns (fuscous) to blackish browns. Base of tail and uppertail- and lowertail-coverts white, remainder black with narrow whitish terminal band. Wings, primaries, and secondaries dark brown; variable buff tans and browns form a finely barred pattern over much of wings (Friedmann 1950, Beissinger 1988). Plumage of older females (≥ 10 yr) tends to become more like Definitive Basic male; plumage is dark throughout but retains a dark brown rather than blackish slaty tone; white superciliary is lost, and head becomes almost black, but a light throat area is retained, and most streaking on breast merges, leaving few very narrow, light streaks (PWS, REB).

Schedule And Order Of Molting

Little information. Few if any other raptors of comparable size undergo either partial or complete molt of flight feathers in fall/winter after hatching. Many raptors do not undergo any body molt in first fall/winter (or following spring). This, in concert with contradictions between Bent’s (1937) and Beissinger’s (1988) description of molts and plumages in Snail Kites, suggests that Snail Kites do not undergo partial body molt (probably Prebasic I molt) in fall/winter after hatching; instead, more likely that changes in appearance in months after hatching result from feather wear, as noted by Bent (1937). Subsequently, Snail Kites probably have 1 complete Prebasic molt annually in spring/summer and fall, Prebasic II (and possibly Prebasic III) molt leading to a predefinitive “subadult” plumage (i.e., first Definitive plumage either third or fourth Basic plumage) (C. W. Thompson pers. comm.). G. Smart (in Sykes 1979), stated that captive males from Argentina acquired Definitive plumage in fourth year (i.e., probably after Prebasic III molt).

Given that most raptors the size of Snail Kites exhibit serial descendant molts, it would not be surprising if Snail Kites replace only some rather than all remiges during Prebasic II and later molts (contrary to Beissinger 1988); rectrices may or may not be replaced completely. However, because of the subtropical distribution of Snail Kites, they may be able to undergo a more complete molt than more northerly distributed raptors of similar size. In absence of any data to the contrary, best to follow Beissinger (1988).

Bill And Gape

Hatchlings: bill decidedly hooked and black with white egg tooth, cere and mandibular rami yellow, and gape and tongue orange-pink. Nestlings 2 wk and older and flying young same as hatchling but without egg tooth. Adults: bill black, narrow in width and depth, strongly down-curved, acutely sharp. Gape and tongue orange-pink. Adult female cere and mandibular rami yellow, except orange during breeding; adult male yellow to orange except scarlet or ruby during breeding (Bent 1937, Friedmann 1950, Beissinger 1988, PWS).

Iris

Dark brown in nestlings and younger flying immatures, becoming more orange in older immatures. Adult female orange to carmine in older individuals; adult male carmine (Friedmann 1950, Beissinger 1988, PWS). Age at which color changes occur not known.

Bare Skin On Head

Lores feathered in nestlings and all immature birds, but sparsely feathered in adults. Skin of lores and eyelids yellow in adult female, becoming orange during breeding, and in adult male yellow to orange, becoming scarlet or ruby during breeding; these colors are about the same as cere color for respective sexes at given time (Friedmann 1950, PWS).

Legs And Feet

Same color as cere in all ages and plumages (Beissinger 1988). Talons from hatching until about 14–21 d of age are pale gray, thereafter black (PWS).

None described.