Appearance

Slate-throated Redstart is one of 12 species of Myioborus redstarts (also known as "whitestarts") noted for their animated foraging displays in which they droop their wings, pivot from side to side, and erect and spread their tails to reveal the white patches in the outer tail feathers. Slate-throated Redstart is distinguished from other species in the genus by its slate gray throat and its chestnut or tawny crown patch. Color of the breast and belly varies geographically, from intense vermilion in birds of northern and central Mexico to yellow in South American birds (see Geographic Variation).

Slate-throated Redstart is most likely to be confused with Painted Redstart (Myioborus pictus), as these are the only two species of Myioborus with a dark (black or slate gray) throat. Slate-throated Redstart, however, lacks the glossy black mantle, conspicuous white wing patches, and white eye crescent characteristic of Painted Redstart, and Painted Redstart lacks the chestnut or tawny crown patch of Slate-throated Redstart. The two species regularly co-occur only in the mountains of Mexico, Guatemala, Honduras, El Salvador, and northern Nicaragua.

Adult: 13-14 cm. Sexes similar. Face and throat blackish gray. Crown gray, with central chestnut or tawny patch. Upperparts dark grayish black. Rictal bristles long, averaging 8-11 mm. Wing feathers and central rectrices black, but the outer 2-4 rectrices broadly tipped in white. Color of the breast and belly varies geographically (Curson et al. 1994; see Geographic Variation). Birds from northern and central Mexico have red or vermilion underparts. In Central America, breast and belly color grades from reddish orange, salmon, and orange (in southern Mexico, Guatemala, Honduras, and El Salvador) to yellowish orange (Costa Rica and western Panama). Breasts and bellies are typically yellow in all South American populations. The extent of white in the outer tail feathers also varies geographically; birds from southern Mexico and northern Central America have relatively little white in the tail, but the extent of white increases in populations to both the north and south (see Geographic Variation). Vent and undertail coverts dark gray, broadly barred with white.

Juvenile: Recently fledged young lack the chestnut crown patch; the head is sooty gray, the upperparts are grayish brown , and the underparts are dull buff (Stiles and Skutch 1989, Curson et al. 1994). The juvenile plumage is short lived, and the immature molts into characteristic adult plumage at about the time it reaches independence (see Molts).

Few published data on molt are available, but Slate-throated Redstart, like many migratory warblers that breed in North America, appears to have a Complex Basic Strategy (Howell et al. 2003) in which adults undergo a complete post breeding (prebasic) molt (Curson et al. 1994, Ryder and Wolfe 2009). In Monteverde, Costa Rica, some adults initiate primary molt at the end of the nesting season in late May or June (R. L. Mumme, unpublished data). Five adults collected from northern Colombia (Departments of Magdalena and Santander) 25 July – 11 August and housed in the Carnegie Museum of Natural History were molting primaries and rectrices when collected (R. L. Mumme, unpublished data).

Recently fledged juveniles begin a partial preformative molt (Ryder and Wolfe 2009) at about the same time they are becoming nutritionally independent of their parents. Flight feathers of the wing and tail are retained, but juvenile body feathers are replaced, at which time birds acquire the brightly colored underparts and chestnut crown patch characteristic of adults.

Iris: black to dark gray

Bill: black

Tarsi and toes: black

Measurements of wing chord and tail length for the 12 recognized subspecies (see Geographic Variation) are provided in Table 1 below. The data are derived from museum specimens except for subspecies comptus, for which the data are from measurements of birds captured and banded in Monteverde, Costa Rica, 2000-2004 (R. L. Mumme, unpublished data). Mean ± SD of body mass for Costa Rican birds is 9.6 ± 0.5 g for males (n = 63) and 9.3 ± 0.6 g for females (n = 57). Wing chord is strongly sexually dimorphic (Figure 1) and is the most useful morphological character for determining sex of birds in the hand.