- Order: Passeriformes
- Family: Thamnophilidae
- Polytypic 2 Subspecies
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.
Both males and females are highly vocal and respond vigorously to conspecifics and playbacks. The most common song of the Western Slaty-Antshrike is its territorial song or 'loud-song' (Oniki 1975), which is a series of 'uh' notes ending with a single 'erk' at a higher pitch (Oniki 1975). The loud-song is produced throughout the day, although is most common in the morning hours, and can be heard throughout the year. The syllable rate of loud-songs does not vary by sex but does show wide variability, ranging from 6.9 syllables/second to 13 syllables/second (See Table 1 for examples; JPK and CET, unpubl. data). The loud-song also is sung as a whisper-song or faint-song (lower in amplitude). Whisper-songs are sung during courtship, feeding of offspring, and as a way for males and females to communicate when foraging.
Development of loud-song
Juveniles less than one year old produce a higher-pitched and more 'squawky' version of the adult loud-song. Development of the loud-song begins by repeating the 'uh' notes that comprise the primary trill. At about 2-3 months after leaving the nest, the loud-song is recognizable as such but still lacks the final 'erk' note. The 'erk' notes begins to be produced by 4-6 months, but the high pitch and 'squawkiness' remains (example: XC49877, JPK). It is also about this time when the total energy present in the first harmonic (~2000 Hz) begins to be emphasized. This can be seen by comparing sonograms of the loud-song of a 4-6 and a 6-8 month old juvenile (example: XC49876, JPK).
One of the most commonly heard vocalization is the reverse-song or 'chirr' (Oniki 1975; play sound: XC2821, D. Bradley; see Table 1). This call is the temporal reverse of the loud-song in that it begins with a single 'erk' and is followed by 'uh' notes. This call is given when the adults are disturbed, such as when they lose a piece of prey, are flushed off a nest by a predator, or when their mate fails to respond to contact calls (Oniki 1975; CET, pers. obs.). Adults also have two single note call types. The first is a single 'grunt' produced at low amplitude and used primarily as a contact call between mates, as a courtship feeding signal, or to communicate with fledglings. These short-duration 'grunt' notes are most often repeated at a moderate rate (2-3 notes per second) during contact calling but can be repeated at higher rates (4-6 notes per second) by a male about to courtship feed the female. The second single-note call of the Western Slaty-Antshrike is a high-amplitude 'caw' that is most often repeated twice or three times in sequence (example: XC2822, D. Bradley; See Table 1). These call sequences are most often given when a predator (or human) is near their offspring. During close range encounters with territorial intruders, Western Slaty-Antshrikes display aggressively using a distinct snarling sound while also posturing and showing their white back patch. In a territorial encounter they also 'meow,' which is a single note call. In addition to the 'caw' calls, they also respond to proximate danger (e.g. direct disturbance to nestling or fledgling) using a temporally variable call series that can be best described as a 'warble' (CET and JPK, pers. obs.). Frantic in pace and variable in pitch, 'warbles' are the unmistakable indication of a nearby young fledgling or the presence of a nest about to fledge young. When given near a nest, the 'warble' call is often accompanied by an enthusiastic 'broken wing' or distraction display. A good example of this 'warble' was recorded by S. Olmstead in Ecuador (play: XC27096, S. Olmstead; See Table 1).
A large collection of vocalizations of the Western Slaty-Antshrike across its distributional range is available from xeno-canto and the Macaulay Library at the Cornell Lab of Ornithology. Those vocal sounds described in the above text are presented in Table 1 for reference.
|Vocal sound||Context||Xeno-Canto Cat. #||Play sound||View sonogram|
|"caw" call||nest disturbance||XC2822||play ||view|
|reverse song ("chirr")||various contexts; general disturbance (prey loss, social intrusion)||XC2821||play||view|
|"warble" call||nest defense and predator distraction||XC27096||play ||view|
|loud-song of 4-6 month old juvenile||territorial||XC49877||play||view|
|loud-song of 6-8 month old juvenile||territorial||XC49876||play||view|
|loud-song of female (fast trill song)||territorial||XC49857||play||view|
|loud-song of male (slow trill song)||territorial dispute||XC49856||play||view|
There is no significant microgeographic variation in loud-song structure between sites in central lowland Panama (JPK, unpublished data), suggesting that dialect formation via vocal learning does not exist. Exemplars from elsewhere in the distributional range (from xeno-canto archives) indicate some variation in the temporal structure of songs.
Both male and female Western Slaty-Antshrikes sing year-round as they aggressively defend their territories. In April-May, before the beginning of the peak breeding season, song rates increase. Responsiveness to playback is high at this time and wanes only slightly throughout the breeding season. The various calls can be heard year-round, but some calls such as the 'warble' call (See 'Calls' above) are given only during the late part of the nesting cycle.
Singing and other vocalizing takes place throughout the day. Singing is not confined to the dawn chorus.
Places of vocalizing
Western Slaty-Antshrikes vocalize from a variety of locations within their territories. Adults broadcast their territorial loud-songs from any strata in the forest, but they tend to sing from the midcanopy. As noted above, 'warble' calls are given in the vicinity of the nest.
Repertoire and delivery of songs
Depending on context, loud-songs (see above for description) can be broadcast with varying amplitude. Territorial males often are the first to respond to a neighboring male's loud-song, and they do so with high amplitude loud-song. Females often follow the male in loose counter-singing. Once females joins a territorial dispute, she often sings a low amplitude loud-song before engaging in high amplitude loud-song. Young individuals often are more aggressive singers, singing higher amplitude loud-songs at faster rates. Old individuals often sing at markedly low rates and seldom approach intruders (or playbacks) (JPK and CET, unpubl. data). In response to playbacks of loud-song, nonterritorial individuals (floaters) often respond with very low amplitude song from a very short distance.
Social context and presumed function
Neighbor-stranger recognition in Western Slaty-Antshrikes only recently has been attempted (JPK, unpubl. data), but no published evidence so far exists. Preliminary evidence from a number of playback studies suggests that response to territorial intruders may be related to the age of both resident and intruder (JPK and CET, unpubl. data). For more information about context of specific vocalizations, see above.
Discrimination between conspecifics and heterospecifics has not been tested in the Western Slaty-Antshrike.
Detailed Description (appearance)
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).
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).
|Sex||Age||Metric||Mean (mm)||St. Deviation||N||Range|
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).
Until 1997, atrinucha was grouped into the larger "Slaty Antshrike" Thamnophilus punctatus sensu lato complex, a suite of more than 11 taxa distributed from Belize to south to southeastern Brazil. Following an analysis of geographic variation in plumage and vocalizations by Isler et al. (1997), the punctatus complex was broken into no fewer than six separate species. Of these, the Western Slaty-Antshrike T. atrinucha is the northernmost member of the complex, and is the only member of the group that is distributed west of the Andes.
Thayer and Bangs (1905) described the population from Gorgona Island, off the west coast of South America, as a separate subspecies, gorgonae. This subspecies is similar to nominate atrinucha, but in the male the forecrown is more extensively gray, and the underparts are lighter gray. Female gorgonae by a darker color on the underparts (with the throat only slightly paler than the breast), a more rufous back, and a much darker crown (Cory and Hellmayr 1924, Zimmer and Isler 2003). Recordings of the vocalizations of gorgonae are not known, and so this taxon was not included in the analysis of geographic variation by Isler et al. (1997).
Described as Thamnophilus atrinucha by Salvin and Godman in 1892, with a type locality of "Central America"; the type locality later was restricted to Panama by Hellmayr in 1911.
The genus Thamnophilus is composed of 27 species, all of which are insectivorous, socially monogamous, sexually dichromatic, and exist in the under- to midstory of forest interiors, edges, or scrub (Remsen et al. 2006, Brumfield and Edwards 2007). The genus appears to be monophyletic (Zimmer and Isler 2003, Moyle et al. 2009). Atrinucha is not particularly closely related to other taxa with which it formerly was included in the same species as "Slaty Antshrike" Thamnophilus punctatus sensu lato (see Geographic Variation). Rather, the sister species to atrinucha is Black-hooded Antshrike Thamnophilus bridgesi (Brumfield and Edwards 2007).
Thamnophilidae (typical antbirds) consists of 209 species, and is within the infraorder, Furnariides, a large Neotropical clade of 600 species.
Tarwater, Corey E., and J. Patrick Kelley. 2010. Black-crowned Antshrike (Thamnophilus atrinucha), Neotropical Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of Ornithology; retrieved from Neotropical Birds Online: http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=369186