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A Close Look at the Bicolored Antvireo: Behavior Plumages and More

The Bicolored Antvireo, also known by its scientific name Dysithamnus occidentalis, is a bird species found in the tropical forests of South America. This bird species has an interesting behavioral trait – they follow army ant swarms to feed on insects that are hiding from the predator.

In this article, we will look at the identification of Bicolored Antvireo, its plumages, and its molts to help you become more knowledgeable about this bird.

Identification

Field Identification

The Bicolored Antvireo is a small bird, approximately 11-13 cm in length. It has a distinct black and white plumage pattern that makes it easy to identify.

The head, neck, and upperparts are black, while the underparts are white. The wings have white tips, and the tail is black with white corners.

Similar Species

One bird species that is often confused with Bicolored Antvireo is the White-flanked Antwren. However, the White-flanked Antwren has a more significant body size, reaching up to 14 cm in length.

Its plumage is also different, with white feathers on the flanks and a larger white wing patch.

Plumages

The Bicolored Antvireo has a unique plumage pattern that makes it easy to identify. However, this species has different plumages that change during different seasons and age.

Adult Plumage: The adult plumage is black above with a white belly and is separated by a clear grey line. Females have a grayish-brown crown.

The wings have pale tips, and the tail is black with white corners. Juvenile Plumage: Juvenile Bicolored Antvireos have a similar pattern to adults, except for the belly.

The belly has a pale yellow color, unlike the adult’s white belly.

Molts

The Bicolored Antvireo undergoes a complete molt of its feathers every year. The timing of molt varies depending on the location, but it usually occurs between February and September.

Breeding Plumage: During breeding season, male Bicolored Antvireos undergo a post-breeding molt, which is a partial molt that affects feathers in the body’s upper parts. This molt occurs between June and July.

Winter Plumage: During winter, Bicolored Antvireos undergo a pre-basic molt, which is a complete replacement of feathers. This molt occurs between September and February.

Conclusion

The Bicolored Antvireo is a unique bird species found in the tropical forests of South America. Its black and white plumage pattern makes it easily identifiable.

Understanding the different plumages and molts can help birders and researchers better understand this species, its behavior, and its ecology. Whether you are a birdwatcher or just enjoy learning about unique bird species, the Bicolored Antvireo is a species worth studying.

Systematics History

The Bicolored Antvireo, scientific name Dysithamnus occidentalis, belongs to the Thamnophilidae family of passerine birds. It was first described by the German ornithologist Jean Cabanis in 1866.

The genus Dysithamnus consists of 13 antvireo species found in South and Central America. The species name “occidentalis” means western in Latin, referring to its distribution in western South America.

Geographic Variation

The Bicolored Antvireo shows little geographic variation throughout its range. However, there is some variation in the size and coloration of the plumage.

Birds from the northern part of its range tend to be slightly smaller and have a darker plumage compared to those in the southern parts.

Subspecies

There are two recognized subspecies of the Bicolored Antvireo:

Dysithamnus occidentalis occidentalis: Found in the western Andes mountains from Colombia through Ecuador, Peru, and into northern Chile. Dysithamnus occidentalis albosuperciliaris: Found in the southern Andes of Argentina and Chile.

The subspecies D. o.

occidentalis and D. o.

albosuperciliaris differ slightly in plumage coloration. D.

o. occidentalis has a distinct white eyebrow stripe, while D.

o. albosuperciliaris has a slightly tinged buff-white eyebrow stripe.

Related Species

Antvireos belong to the family Thamnophilidae, which includes many species of insectivorous passerine birds found in Central and South America. The genus Dysithamnus consists of 13 antvireo species found in Central and South America.

The Bicolored Antvireo is closely related to the widespread Rufous-winged Antvireo (Dysithamnus coccothraustes), which can be found from Mexico to Bolivia and Brazil.

Historical Changes to Distribution

The Bicolored Antvireo is a resident bird species of the Andes of South America, with a range from Colombia to Argentina and Chile. The species inhabits dense, humid forests and forest edges at altitudes ranging from 800 to 2500 meters.

Habitat loss due to deforestation, logging, and the conversion of forests to farmland are the primary threats to the Bicolored Antvireo population. Despite these threats, the Bicolored Antvireo is listed as a species of least concern on the IUCN Red List due to its widespread distribution and large population.

There are few records of historical changes in the distribution of the Bicolored Antvireo. However, one study conducted in the 1970s found that the species was absent in the north-central Andes of Colombia, where it had been previously reported.

The study hypothesized that the absence of the species in the region could be attributed to changes in vegetation caused by human activities. Additionally, another study found that the density of Bicolored Antvireos in some parts of the Andes had decreased.

The study suggested that the decline in density could be due to habitat loss. Climate change is another factor that could have an impact on the distribution of the Bicolored Antvireo in the future.

As temperatures continue to warm, the vegetation zones could shift to higher altitudes. This could lead to a reduction in suitable habitat for the Bicolored Antvireo.

However, more research is needed to understand the potential impact of climate change on the species. In summary, the Bicolored Antvireo is a species with a relatively stable distribution throughout its range.

However, the species is threatened by habitat loss caused by human activities. Understanding the genetic variation, the subspecies, and the related species can provide important information to better protect and conserve this species.

Moreover, historical changes in the species’ distribution help us understand its biology and ecology, which can inform future conservation efforts.

Habitat

The Bicolored Antvireo is a bird species that is commonly found inhabiting dense and humid mountainous forests in the Andes of South America. This species predominantly occurs at elevations between 800-2500 meters above sea level.

Forests are preferred by this species for the provision of the nest-building materials, food, and cover from predators.

Movements and Migration

The Bicolored Antvireo is a non-migratory bird species. This means that it does not undertake regular seasonal movements between breeding and non-breeding grounds.

However, it might exhibit some altitudinal migration during the non-breeding season; that is, it moves to higher altitudes where it can exploit food resources better. As assumed, Bicolored Antvireos are sedentary, meaning that they remain within the same geographic location year-round.

This sedentary lifestyle exhibits that this species has evolved to depend on the resources available in its habitat year-round for survival. It is suggested that Bicolored Antvireos do not need to undergo migration to find food because they follow ants and other swarming insects, which they feed on.

Bicolored Antvireos are typically observed in pairs or small family groups, and they defend their territories throughout the year. Therefore, it is important that Bicolored Antvireos remain within their territories year-round to defend them from intruders and exploit their resources effectively.

Although Bicolored Antvireos do not undertake regular seasonal movements, recent studies have indicated that they undertake local movements. A study conducted in Ecuador found that the Bicolored Antvireos occupancy was different between different locations within the same region and even differed at different times of the year.

This evidence suggests that Bicolored Antvireos undertake local movements to exploit the rich and diverse resources available across different locations within their range.

In Sum

The Bicolored Antvireo is a non-migratory species that remains in the same geographic location throughout the year. Its sedentary lifestyle allows it to defend its territories effectively and access resources such as ants and other swarming insects essential to its survival.

Even though it does not undergo regular seasonal movements, it may undertake local movements during the non-breeding season to exploit the rich and diverse resources across different locations within its range.

Diet and Foraging

Feeding

The Bicolored Antvireo is a bird species that primarily feeds on insects. This bird obtains insects through active foraging and is frequently found following ant swarms to feed on insects that are fleeing from the foraging ants.

Additionally, the Bicolored Antvireo also feeds on other insects such as beetles, spiders, and grasshoppers. The Bicolored Antvireo forages actively in the understorey and mid-storey levels of its forest habitat, often clinging to twigs and leaves while searching for insects.

The species also probes dead leaves and twigs for insects.

Diet

Although the Bicolored Antvireo’s diet primarily consists of insects, the species has also been observed feeding on small fruits and nectar. The species can also consume small vertebrates, including lizards and frogs.

The Bicolored Antvireo’s feeding habits are unique compared to other bird species in that it follows ant swarms during foraging. The species feeds on insects that are escaping predators such as ants and other small animals.

This feeding strategy has enabled the species to access a variety of insect species that are not typically consumed by other bird species.

Metabolism and Temperature Regulation

The metabolism of the Bicolored Antvireo is essential for the species to maintain its body temperature in its natural range. Metabolism is the process by which energy is produced in the body to meet the physiological needs of the animal.

Bicolored Antvireos have high metabolism compared to other bird species. This high metabolism is necessary for them to maintain their body temperature in cold forest environments.

Endothermic animals such as birds regulate their body temperature through metabolic processes. This means that birds maintain a constant internal body temperature by producing metabolic heat or dissipating excess heat.

The Bicolored Antivireo’s high metabolic rate enables it to maintain its optimum body temperature, which is essential for its survival in the cold mountainous forests where it habituates.

Sounds and Vocal Behavior

Vocalizations

The Bicolored Antvireo communicates with other members of its species through a variety of vocalizations. The species vocalizes primarily during the breeding season to communicate with potential mates and defend territories.

The Bicolored Antvireo has a repertoire of vocalizations that includes songs and calls. The song of the male Bicolored Antvireo is a series of phrases, consisting of four to seven notes, with a sharp “tsip” or “zip” note.

The song is repeated regularly throughout the day and is used to attract mates and defend territory. The female Bicolored Antvireo has a different song, which consists of a series of warbling notes.

The female song is believed to be used to signal her readiness to mate and defend her territory. Apart from songs, the Bicolored Antvireo also has a variety of calls that it uses to communicate with other members of its species.

These calls include a contact call, a territorial call, and an alarm call. The contact call is used to keep track of other members of the species within the territory, while the territorial call is used to defend the territory from intruders.

The alarm call warns of incoming danger, often from predators such as hawks or snakes. In summary, the Bicolored Antvireo is primarily an insectivore that follows ant swarms during foraging.

The species has a unique feeding strategy and foraging behavior in its habitat. Additionally, the species has high metabolic rates, which is necessary to maintain its body temperature in the cold mountainous forests where it habituates.

The species uses a variety of vocalizations to communicate with other members of its species, including different songs and calls for mating and territorial communication.

Behavior

Locomotion

The Bicolored Antvireo has a hopping and climbing locomotion. This bird is typically observed clinging to leaves and twigs while foraging, moving through the vegetation cautiously in search of insects.

Self-Maintenance

The Bicolored Antvireo engages in self-maintenance activities such as preening and bathing. Preening is an essential self-maintenance behavior that involves the cleaning, oiling, and alignment of feathers in birds.

Preening helps to keep feathers clean and healthy and also helps to maintain their functionality in flight. Bathing is another self-maintenance behavior that involves water immersion for cleaning the feathers and removing dirt and parasites.

Agonistic Behavior

The Bicolored Antvireo is a territorial bird that engages in agonistic behavior to defend its territory from intruders. Agonistic behavior includes displays such as wing spreading, tail fanning, and vocalizations such as alarm calls, territorial calls, and aggressive singing.

These behaviors are used to intimidate intruders and warn them to stay away as well as to attract mates.

Sexual Behavior

The Bicolored Antvireo is a monogamous bird species. During the breeding season, pairs of Bicolored Antvireos engage in displays of courtship behavior such as chasing, calling, and singing.

The male also presents food to the female as part of the courtship ritual. Once pair-bonded, the Bicolored Antvireos begin building their nest.

Breeding

The Bicolored Antvireo breeds from March through July, with a peak breeding period occurring between May and June. Nests are built by both the male and female, with the male collecting the materials and the female constructing the nest itself.

The nest is typically built in the understorey or mid-story levels of the forest, often on twigs or vines hanging over streams or ravines. The clutch size of the Bicolored Antvireo consists of two eggs.

These eggs are incubated by both the male and female for approximately 15-17 days. Once hatched, the chicks are altricial and completely dependent on their parents for food and care for approximately 14-20 days.

Demography and Populations

The Bicolored Antvireo is currently listed as a species of least concern on the IUCN Red List. However, deforestation and the loss of habitat are major threats to the species’ populations.

The construction of roads and the conversion of forests to agricultural land also pose a significant threat to the conservation of this species. Population trends for the Bicolored Antvireo are not well documented, with more information needed to assess the species’ population and its trends accurately.

Improved environmental policies and habitat conservation efforts are urgently needed to preserve this species and its habitat, which is essential for the survival of many other bird and animal species in the Andean mountain forests. The Bicolored Antvireo is a fascinating bird species that inhabits the Andean mountain forests of South America.

This species has a unique foraging strategy, following ant swarms to feed on insects and has a high metabolic rate necessary for its survival in the cold forests where it lives. The Bicolored Antvireo engages in self-maintenance, agonistic, and courtship behaviors as part of its day-to-day life.

The species builds nests, lays eggs, and rears its young to perpetuate the next generation. While listed as a species of least concern, the Bicolored Antvireo faces numerous threats, including habitat loss and degradation.

Therefore, long-term conservation measures, environmental policies, and efforts are necessary to protect the Andean forests and other endangered species that cohabit with this fascinating bird. Conservation investments and policies are not only crucial for preserving biodiversity, but they also provide ecological, economic, and social benefits to people and the planet.

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