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5 Reasons to Admire the Chestnut-Shouldered Antwren

The Chestnut-shouldered Antwren (Euchrepomis humeralis) is a small passerine bird that belongs to the antbird family, Thamnophilidae. This bird species is known for its distinctive chestnut-colored patch on its shoulder, which makes it easy to identify, and it can be found across South America, living in humid forests in lowland areas.

Field Identification:

The Chestnut-shouldered Antwren has a distinctive appearance that makes it easy to identify even for novice birdwatchers. It measures approximately 12-13 cm in length and has a short tail.

It has a black head, a gray body, and a white belly. The most notable feature is the chestnut-colored patch that extends from the shoulder to the wing.

Similar Species:

The Chestnut-shouldered Antwren is easily differentiated from other antbirds due to its unique plumage. However, there are a few species that share some similarities in appearance that may cause confusion.

The White-flanked Antwren (Myrmotherula axillaris), is a similar-looking species that also has a white flank patch, but its shoulder patch lacks the chestnut hue of the Chestnut-shouldered Antwren. Plumages:

The Chestnut-shouldered Antwren has a distinctive plumage that changes with age.

Juveniles have a similar appearance to adults, but their plumage is duller, and their shoulder patch is not as prominent. Male and female adults share the same appearance.

This species doesn’t go through a dramatic change in its plumage during the year, unlike other bird species that have a breeding and non-breeding plumage. Molts:

Birds molt their feathers periodically to replace damaged and worn-out ones.

The Chestnut-shouldered Antwren goes through two molts per year; the pre-basic molt and the pre-alternate molt. The pre-basic molt takes place after the breeding season, and the pre-alternate molt occurs before the breeding season.

During the pre-alternate molt, males display brighter plumages as they prepare for the mating season. This is when the Chestnut-shouldered Antwren showcases the prominent chestnut patch on its shoulder.

In conclusion, the Chestnut-shouldered Antwren is a beautiful bird species with a conspicuous plumage that makes it easy to identify. Its unique shoulder patch and its distribution across South America make it an interesting bird to observe for naturalists and bird enthusiasts alike.

While its molting pattern may not present a significant change in plumage, it highlights the importance of proper feather maintenance to enable better flight and insulation for these tiny birds. Systematics History:

The Chestnut-shouldered Antwren (Euchrepomis humeralis) was first described by the French ornithologist, Louis Jean Pierre Vieillot in 1816.

It belongs to the family Thamnophilidae, which is a diverse group of passerine birds found primarily in South and Central America. Despite being relatively well-documented, the classification of the Chestnut-shouldered Antwren has been subject to several changes over the years as taxonomic and genetic analyses have advanced.

Geographic Variation:

The Chestnut-shouldered Antwren has a wide distribution range across South America. However, the species’ plumage shows notable geographic variation.

The birds in the northwestern region of the species’ range have a more extensive white belly patch than those birds in the central and southern range. The subspecies Euchrepomis humeralis pelzelni, which is found in Peru and Ecuador, has a white malar stripe that distinguishes it from the other subspecies.

Subspecies:

There are five recognized subspecies of the Chestnut-shouldered Antwren based on plumage variation and geographic range:

1. Euchrepomis humeralis bahiae, found in eastern Brazil, is paler with a slightly smaller chestnut patch.

2. Euchrepomis humeralis duidae, found in northern and central Brazil, is larger with a more extensive white belly patch.

3. Euchrepomis humeralis humeralis, found in central and southern Brazil, is the nominate subspecies and has the most prominent chestnut patch.

4. Euchrepomis humeralis naumburgae, found in western Colombia and northern Ecuador, has a smaller chestnut patch and paler underparts.

5. Euchrepomis humeralis pelzelni, found in Peru and Ecuador, has a white malar stripe and a small chestnut patch.

Related Species:

The Chestnut-shouldered Antwren is closely related to other species of antbirds in the genus Euchrepomis, including the Stripe-shouldered Antwren (E. callinota) and the White-shouldered Antbird (E.

sharpei). These species share a similar body shape and size and are found in similar habitats, but they have different plumage patterns and vocalizations.

Historical Changes to Distribution:

The Chestnut-shouldered Antwren’s range has likely remained somewhat stable over the years, as it is still found across South America, though it may have undergone slight changes. There are, however, significant regional changes that have affected the populations in specific areas.

Deforestation and habitat loss are the primary factors that have contributed to changes in habitat availability for the Chestnut-shouldered Antwren.

While specific details on historical distribution are scarce, recent research shows significant declines in populations.

A study published in 2019 concluded that the Chestnut-shouldered Antwren is rapidly declining in abundance and range across Brazil. The paper attributes this decline to the species’ association with Atlantic Forest, the most threatened biome of Brazil, where significant habitat loss has occurred.

Additionally, another study in 2020 highlighted the Chestnut-shouldered Antwren as one of 92 bird species at risk due to predicted deforestation in the Amazon. It is predicted that the core range of the species will be lost if deforestation continues at current rates.

In conclusion, despite having a widespread distribution, the Chestnut-shouldered Antwren has faced significant declines in population size and range. The species has undergone several taxonomic changes, and its plumage shows notable geographic variation.

Ongoing habitat destruction is the primary threat to the continued survival of this species. Future conservation efforts must prioritize habitat preservation to prevent further declines in population size and range.

Habitat:

The Chestnut-shouldered Antwren is primarily found in humid forests in lowland areas across its range in South America. It prefers dense undergrowth, particularly in the understory, and can also be found along forest edges and in secondary growth forests.

The species does not tolerate extensive habitat degradation and is considered vulnerable to habitat loss.

The Chestnut-shouldered Antwren’s primary habitat requirement is a dense, moist understory.

It is absent from open areas, as it prefers to remain hidden in vegetation most of the time. This bird is not known to make use of human-made habitats such as plantations, gardens, or parks.

Movements and Migration:

The Chestnut-shouldered Antwren is primarily a resident species, meaning it does not undertake long-distance migration. The species is generally sedentary, and most populations do not make any significant movements throughout the year.

However, there is one instance of migratory behavior in the subspecies Euchrepomis humeralis bahiae. This subspecies is known to disperse from eastern Brazil during the dry season, expanding its range into the south and west, before returning to its original range during the wet season.

These movements are likely driven by seasonal changes in resource availability and nesting opportunities. Aside from these seasonal movements, Chestnut-shouldered Antwrens are highly territorial and do not generally disperse far from their home range.

Juvenile birds may disperse further from their natal habitat, but this is not well-documented. The Chestnut-shouldered Antwren does migrate locally in response to the availability of resources within its habitat.

This species may undertake daily movements to search for food sources or move to areas with more favorable climatic conditions. The birds move vertically within their habitats, changing heights and locations to maximize their feeding opportunities, and to avoid predators.

The Chestnut-shouldered Antwren may also undertake short flights to escape predators or defend its territory against incoming birds, though its ability to fly long distances has not been extensively documented. In conclusion, the Chestnut-shouldered Antwren is primarily a resident species that does not undertake long-distance migration.

However, seasonal migratory behavior of the subspecies Euchrepomis humeralis bahiae suggests that resource availability and nesting opportunities may influence movement patterns. The species’ ability to move vertically within its habitat and disperse locally suggests flexibility in response to changes in resource availability.

Ongoing habitat destruction and degradation have likely limited the species’ movement potential, making habitat preservation a priority for its conservation. Diet and Foraging:

Feeding:

The Chestnut-shouldered Antwren is an insectivorous species that feeds primarily on a diet of insects, arthropods, and spiders.

This species feeds mainly on the ground or in mid-level vegetation, primarily in the understory of dense forests. The Chestnut-shouldered Antwren catches its prey using a rapid and agile flight pattern, often taking insects in flight and snatching them out of the air.

The birds may also glean insects from the surfaces of leaves or bark or pick them from the ground. Diet:

The Chestnut-shouldered Antwren feeds mainly on small to medium-sized insects such as beetles, ants, spiders, and grasshoppers.

This species is known to be an opportunistic feeder, taking advantage of whatever insects are available within the habitat. Chestnut-shouldered Antwrens often forage in flocks of mixed species, and this behavior helps them locate food sources and utilize resources most efficiently.

Metabolism and Temperature Regulation:

The Chestnut-shouldered Antwren is a small species known for its high metabolism and the ability to maintain a constant body temperature. Due to their small size and high surface-area-to-volume ratio, small birds like the Chestnut-shouldered Antwren lose body heat more readily than larger birds.

This species, therefore, has high metabolic rates that enable it to maintain a high body temperature.

The birds regulate their temperature by basking in the sun, fluffing up their feathers to retain warmth, or seeking shade in hot weather.

They are also known to use spatial variation in their habitats to thermoregulate, moving between microhabitats to stay within their thermal comfort zone.

Sounds and Vocal Behavior:

Vocalization:

The Chestnut-shouldered Antwren has a variety of vocalizations, including songs, calls, and vocalizations used in social interactions.

The birds are known for their complex vocalizations, which often involve fast and complicated sequences of notes or trills. The male’s song is a series of clear, whistled notes that are high-pitched and sweet-sounding.

The songs are often delivered from a high perch or while in flight and are used primarily to establish and defend territory or attract mates. The Chestnut-shouldered Antwren also has several different call notes that it uses in social interactions.

The birds use a sharp “tsip” note to signal to other individuals when feeding, while a more drawn-out “churr” call is used in agonistic encounters or to signal distress. In addition to songs and calls used in social interactions, Chestnut-shouldered Antwren also vocalizes in a duet.

The duet is created when males and females sing together in alternating sequences, often producing a complex and interwoven vocal display. In conclusion, the Chestnut-shouldered Antwren is an insectivorous species that feeds on small insects found mainly on the forest floor.

This species has a high metabolism that allows it to maintain constant body temperature, and it is known to use behavioral and physiological strategies to thermoregulate in different habitats. The Chestnut-shouldered Antwren is also known for its complex vocalizations, including songs, calls, and duets, which are used in both social interactions and territorial disputes.

Behavior:

Locomotion:

The Chestnut-shouldered Antwren is an agile, active bird that moves primarily by hopping and gliding short distances. This species has strong legs and feet that enable it to grasp and hold onto branches and leaves while foraging.

It is also capable of fast, direct flight to escape predators when necessary. Self-Maintenance:

The Chestnut-shouldered Antwren is a fastidious bird that spends considerable time preening and maintaining its feathers.

This behavior is crucial for the bird’s ability to fly, insulate, and protect itself from parasites and diseases. The birds bathe frequently, either in rainwater or in streams, and are known to sunbathe or dustbathe to manage feather parasites.

Agonistic Behavior:

The Chestnut-shouldered Antwren is a territorial species that is known to defend its territories aggressively. The birds use loud calls and displays to warn off intruders and may engage in physical confrontations if the warning displays fail.

These interactions are usually between territorial males and may involve a lot of posturing and vocalizing. Chestnut-shouldered Antwrens will also mob predators to defend their nests.

Sexual Behavior:

The Chestnut-shouldered Antwren mating system is monogamous, with males and females forming long-term pair bonds. The birds have a courtship display that involves the male showing off its chestnut patch, singing, and hopping around the female.

Once a pair bond is formed, the pair will move together around their territory.

Breeding:

The Chestnut-shouldered Antwren breeding season begins at different times across its range but is generally between October and February.

The birds build a small, cup-shaped nest made from plant fibers, which is hidden in dense undergrowth, shrubs, or low tree branches. The female lays two eggs that are incubated by both parents, with the female taking the night shift, and the male taking over during the day.

The incubation period is approximately 15 to 16 days. The young are born altricial, meaning they are blind and featherless and depend on their parents for food and warmth.

Demography and Populations:

The Chestnut-shouldered Antwren populations are classified as being of “Least Concern” by the IUCN Red List. Although there is widespread habitat loss throughout its range, this species is generally considered to be relatively resilient to disturbances.

However, some populations of Chestnut-shouldered Antwrens are experiencing declines in population size, particularly in areas where habitat loss is significant. A combination of deforestation, climate change, and habitat fragmentation represents a significant threat to the species and is likely to cause further declines in the future.

Several conservation measures have been put in place to protect the Chestnut-shouldered Antwren, including the creation of protected areas and habitat restoration efforts. These conservation efforts are essential to the species’ survival, as they provide suitable habitats and prevent further population declin

The Chestnut-shouldered Antwren is an intriguing bird species with a distinctive chestnut-colored patch on its shoulder.

It is known for its residency and behavior such as foraging, thermoregulation, and vocal communications. Additionally, the Chestnut-shouldered Antwren is widely distributed across South America, and its populations are facing threats from deforestation and habitat loss.

However, the species’ resilience to disturbances, protection efforts, and habitat restoration have shown the potential to reduce population declines. The Chestnut-shouldered Antwren species is an excellent example of the importance of conservation efforts, both locally and globally, to support biodiversity and to maintain healthy ecosystems.

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