Appearance

The Western Slaty-Antshrike is a medium-sized antbird with a hooked bill, slaty grey body with a black crown (male) or brown body with chestnut crown (female) (Figure 1).  Juveniles obtain adult plumage by two months after fledging. Instead, juveniles are distinguishable from adults by their immature song and behaviors. Western Slaty-Antshrikes are distinct from other sympatric species based on their body size, hooked bill, and spots on wing and tail.  They nest in the understory and forage primarily in the understory and midcanopy.  They sometimes forage with mixed-species canopy flocks in the high canopy.

Can be confused with the sympatric Dusky Antbird (Cercomacra tyrannina) if seen only briefly. Both species are often seen hopping in dense liana tangles. Dusky Antbirds have more slender bills that lack a prominent shrike-like hooked tip, have less white on the wing, and are more uniform in color than Western Slaty-Antshrikes. To the beginner's ear, the loud-song of Western Slaty-Antshrikes can be confused with Barred Antshrikes (Thamnophilus doliatus), with which they overlap in younger forest habitat. The territorial loud-song given by Western Slaty-Antshrikes seems noticeably lower in amplitude and is considerably more nasal than that of Barred Antshrikes.

Description of Thamnophilus punctatus atrinucha from Panama Canal Zone (Wetmore 1972: 144-149): "With heavy head and body, short tail, and large bill of other species of this genus; distinguished by plain breast, gray in male, and dull buffy brown in the female. Length 140-150mm. Adult male, crown and hind neck black, with forehead partly or wholly gray; side of head gray, with ear coverts streaked narrowly with white; center of back with concealed base of feathers white, tipped broadly with black; upper tail coverts black, tipped with white; rest of upper surface gray; wings black, with wing coverts tipped, and tertials and secondaries edged with white; primaries edged narrowly with gray; tail black with a white spot at the end of each feather; under surface, including edge of wing, slaty gray; under wing coverts, and line of inner webs of remiges, white.  Female (Figure 3), brown to buffy brown above, brighter on the crown; wing coverts fuscous-black, tipped with buff to buffy white; wings fuscous-black, edged with brown; rectrices fuscous-black, edged with brown, and tipped with white or buff; concealed white in bases of feathers of center of back as in the male; under surface buffy brown to grayish brown, paler on throat; under wing coverts and inner edge of remiges buff. Juvenile, dull cinnamon-brown above; duller on throat and sides, with the breast and abdomen grayish white. The male in this plumage is somewhat grayer than the female."

Both males and females have a white back patch that is generally concealed except when in an aggressive encounter or preening. Offspring molt into adult plumage rapidly. By three weeks out of the nest, one can determine the sex of the offspring, and molting into adult plumage is complete by less than two months after fledging (CET, unpubl. data).

Little information is available. Individuals molt throughout the year, overlapping with breeding. But during breeding rarely are more than 1-2 flight feathers molted at a time (CET and JPK, pers. obs.). Long-term netting indicates that in March and July (which mark the beginning and end of the peak breeding season), often there is some head, body, and feather molt during these periods, but it is never extensive. When offspring leave the nest, they appear to look like females but without the chestnut crown and buff parts (only dull brown). By three weeks out of the nest, the fledglings are molting into their adult plumage (see 'Juvenile development', CET, unpubl. data).

The pupil is black with a brownish red to chocolate-brown iris in both sexes. Unlike many related species (e.g. Checker-throated Antwrens, Epinecrophylla fulviventris; Greenberg and Gradwohl 1997), little variation in iris color exists in adults or young. Bill color ranges from dark gray in males to light gray in females, though no quantitative analysis of bill color has been conducted. Tarsi and toes are medium to dark gray in both sexes.

Individuals are roughly 14.5-15 cm long (5 ¾ - 6 inches; Ridgley and Gwynne 1989). The sexes do not differ in any measurements, either as adults or as nestlings (Tables 1 and 2; CET, unpubl. data).