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Chestnut-backed Antbird Poliocrania exsul

  • Order: Passeriformes
  • Family: Thamnophilidae
  • Polytypic: 5 subspecies
  • Authors: Woltmann, Stefan, Ryan S. Terrill, Matthew J. Miller and Matthew L. Brady
Sections

Behavior

Behavior

Locomotion

Generally walks when on ground, otherwise makes short, wing-assisted hops from one perch to the next. Long flights in the understory infrequent (Willis and Oniki 1972). In systematic trials in Lake Gatun, Panama, could not sustain flight for 200 m (Moore et al. 2008).

Foraging

See also "Food Capture and Consumption" above. On Barro Colorado Island (Panama), pairs foraged most often between 5 and 20 m from each other, and rarely < 5 m apart (Stutchbury et al. 2005).

Self-maintenance

The species "preens and rests in dense tangles or near cover," and individuals frequently groom each other (Willis and Oniki 1972). We find no references to bathing in water or in dust.

Agonistic behavior

See also VocalizationsSocial Context and Function. Both males and females in territory or boundary disputes characteristically pound the tail (as in this female [nominate exsul], and note that the video currently misidentifies this as a male), sleek back head feathers and sing and vocalize vigorously (Skutch 1969, Willis and Oniki 1972; e.g., Macaulay Library 63402). The wings may be drooped and the white edge of the wing is made prominent (Skutch 1969), and the feathers of the back and rump may be raised (Wetmore 1972).

Territoriality

Pairs hold jointly defended territories year-round (Willis and Oniki 1972, Marcotullio and Gill 1985, Stutchbury et al. 2005). Territory-switching is uncommon, occurring very rarely during a 5-year study (an average of < 0.10 switches per territory per year) in Costa Rica (SW unpub. data). Males seem to play a larger role in territory defense, though this impression is based on reactions to broadcast of male song (SW). See description of male response to male song in Vocalizations - Social Context and Function.

Published estimates of territory size range from about 1 (Stutchbury et al. 2005) to 7 ha (Robinson et al. 2000), but the latter estimate appears to be based on the assumption that the whole 97-ha plot was occupied, and may be an overestimate. A pair followed with telemetry in Costa Rica (Osa Peninsula) apparently never left a 2 ha study area in over 2 weeks of study (Marcotullio and Gill 1985). In northeastern Costa Rica typical territory size is roughly 1-3 ha, but territory sizes may be smaller when the density of individuals is higher (SW, RST, MLB pers. obs.). The high density of individuals on Barro Colorado Island (ca. 47 pairs-100 ha) suggests territory sizes of 2 ha or less, depending on the amount of habitat available (based on the estimate of 1500 [or 750 pairs] on the ~1600-ha island; Robinson 2001). In Soberania National Park, Panama, Robinson et al. (2000) estimated a density of 13 pairs-100 ha.

Based on a mark-recapture study involving intensive searches for territories (using playback), average population density at the La Selva Biological Reserve in Costa Rica was 9.6 pairs-100 ha between 2006-2009, with little change between years (range 9.3 – 10.0; SW unpub. data). Four other populations sampled nearby had densities ranging from 17.4 – 43.3 pairs-100 ha, with the latter estimate coming from a small (80 ha), and very isolated forest fragment (SW unpub. data).

Sexual Behavior

Mating system and sex ratios

Socially monogamous, and most likely genetically monogamous as well (Russell 2000, Russell et al. 2004). Sex ratios presumably more or less equal, but may be difficult to assess given more secretive behavior of females.

Pair bond

Pairs typically forage within 5-20+ m of each other (Stutchbury et al. 2005; SW pers. obs.). "Mutual grooming is frequent" (Willis and Oniki 1972). A female observed collecting nest material (rhizomorphs) was followed within 5 m by a male who inspected, but did not collect, similar materials (SW pers. obs.).

Courtship display

No courtship display described. Male brings prey items to the female (Willis and Oniki 1972).

Extra-pair copulations

No published information. Extra-pair fertilization likely rare based on 2-egg clutches and extended parental care (Russell 2000, Stutchbury and Morton 2001, Russell et al. 2004).

Social and interspecific behavior

Generally move about as pairs; groups of 3-4 birds likely adults with offspring. When individuals at the edges of territories meet, or in actual territorial disputes, the male sleeks down his head feathers, puffs the dorsal feathers, and sings and calls vigorously, constantly pumping the tail (Willis and Oniki 1972; SW pers. obs.). The exposed blue skin on the head may seem especially prominent, as may the white leading edge of the wing (Willis and Oniki 1972). At antswarms, is displaced from perches by professional ant-following antbirds, with the exception of Spotted Antbird (Hylophylax naevioides), for which Chestnut-backed Antbirds "seem to have a special antagonism" (Willis and Oniki 1972).

Predation

Kinds of predation

Little published; known predators at nests include snakes (Pseustes poecilonotus), White-faced Capuchins (Cebus capucinus), and Coatis (Nasua narica; Robinson et al. 2005). Other likely egg and nestling predators (based on observed events at nests of similar species or in similar habitats) include toucans and aracaris (Ramphastos, Pteroglossus spp.), forest-falcons (Micrastur spp.; Robinson and Robinson 2001) and Double-toothed Kite (Harpagus bidentatus; Tarwater 2008).

Predators of adults likely include various snakes known to take avian prey (e.g., Pseustes, Boa, Spilotes, Bothriechis), various raptors (Micrastur, Accipiter), and mammals (Cebus, mustelids, felids).

Response to predation

Incubating birds flushed off nests often feign injury in an apparent attempt to lure the predator away from the nest (Skutch 1969, Wetmore 1972, SW pers. obs.). Incubating adults may attack snakes attempting to eat eggs or nestlings, but these attempts often not successful (Robinson et al. 2005).

Recommended Citation

Woltmann, Stefan, Ryan S. Terrill, Matthew J. Miller and Matthew L. Brady. 2010. Chestnut-backed Antbird (Poliocrania exsul), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. https://doi.org/10.2173/nb.chbant1.01