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Discover the Rare and Mysterious Brazilian Merganser: From Plumages to Preservation

In the heart of Brazil, there lives a critically endangered species: the Brazilian merganser, also known by its scientific name Mergus octosetaceus. This beautiful bird, with its striking plumage and fascinating life cycle, is a wonder to behold.

In this article, we’ll get up close and personal with this little-known species, exploring everything from its identification to molts and more.



Identification – The Brazilian merganser has a unique body shape, with a long, narrow, and tapered bill. They are about 20 inches long, with a wingspan of 27 inches.

They are usually dark gray, with a green iridescence on their feathers. They have a white band around their neck and a bold, black-and-white striped head.

Similar Species – The Brazilian merganser has a few relatives that might confuse you. The common merganser, for instance, has a similar body shape and bill but has dark feathers with white underparts, rather than being dark gray.

The hooded merganser, another close relative, has a white patch on its head and orange-and-black plumage.


The Brazilian merganser has two distinct plumages and goes through a series of molts throughout its lifespan. Adults – Adults have a unique, iridescent dark-gray body with white markings on their neck, head, and tail.

In breeding season, males have a bright red bill, while females have a duller greenish-brown bill. Juveniles – Juveniles have brown feathers and lack the white neck-band, but they still have the black-and-white striped head.


The Brazilian merganser goes through two molts throughout its lifespan: the nesting and non-nesting molts. Nesting Molt – During the nesting molt, the Brazilian merganser sheds all of its feathers and grows new ones to prepare for breeding season.

This molt usually happens between September and January and takes about three months to complete. Non-nesting Molt – During the non-nesting molt, the Brazilian merganser replaces feathers lost from wear and tear so that it can maintain its feathers’ health and appearance, especially its flight feathers.


The Brazilian merganser is a rare and precious bird that is threatened with extinction. Despite its name, this species does not reside exclusively in Brazil but has a small range that spans Argentina and Paraguay.

Understanding the bird’s identification, plumages, and molts can aid conservation efforts and help us better appreciate the unique and beautiful creature that is the Brazilian merganser. We can only hope that we can preserve this fascinating bird species for future generations to enjoy.

Systematics History

The systematics history of a species refers to the study of its evolutionary lineage and classification. The Brazilian Merganser has a complicated taxonomic history, with the classification changing several times based on new discoveries and genetic evidence.

Geographic Variation

There is little geographic variation in the Brazilian Merganser, although some populations may differ in size or plumage. This is likely due to the species’ isolated range, which has limited gene flow between populations.


There are two recognized subspecies of the Brazilian Merganser. M.

o. octosetaceus: The nominate subspecies, found in the upper Paran and upper Uruguay river basins.

M. o.

irroratus: Found in the upper Paraguay river basin. These subspecies differ mainly in their size, with M.

o. octosetaceus being slightly larger than M.

o. irroratus.

Related Species

The Brazilian Merganser is part of the Merginae subfamily of ducks, which contains other mergansers and smew. The genus Mergus is unique among ducks due to its narrow, serrated bills, which are adapted for catching fish.

One of the Brazilian Merganser’s closest relatives is the Common Merganser (Mergus merganser), which has a similar body shape and bill but has dark feathers with white underparts, rather than being dark gray. The Hooded Merganser (Lophodytes cucullatus) is another close relative, though it has a white patch on its head and orange-and-black plumage.

Historical Changes to Distribution

The Brazilian Merganser’s range has declined over the past century due to habitat loss, human disturbance, and persecution. The species was originally found in the Paran, Uruguay, and Paraguay river basins, but its range has since been restricted to a few select sites within this area.

The Brazilian Merganser is considered critically endangered, with only around 250 individuals estimated to remain in the wild. The majority of these individuals are found in Brazil’s Upper Paran River region, mainly in protected areas such as the Ilha Grande National Park and the Taiam Ecological Station.

In the past, the Brazilian Merganser was more widespread, occurring in several other river systems in Brazil, Argentina, and Paraguay. However, much of the bird’s habitat has been destroyed due to human activities, such as dam construction, logging, agriculture, and mining.

For example, the construction of the It Hydroelectric Power Plant in the 1980s caused a significant decline in the species’ population due to habitat loss and increased human disturbance. Similarly, the Yacyret Dam in Argentina has also had a negative impact on the Brazilian Merganser’s habitat and population.

Efforts are currently underway to protect and conserve the Brazilian Merganser’s remaining habitat. This includes advocacy, habitat restoration, captive breeding programs, and law enforcement to eliminate hunting and other threats to the species.

Despite these measures, the Brazilian Merganser continues to face an uncertain future, with ongoing habitat loss and human disturbance posing significant threats to the species’ survival. If conservation efforts are not successful, this unique and fascinating bird may be lost forever.


The Brazilian Merganser relies heavily on freshwater habitats, typically rivers and streams with clear and fast-flowing waters that offer prime fishing opportunities. Like other mergansers, the species has a narrow, serrated bill that helps it catch fish, which make up the bulk of its diet.

The most important habitat for the Brazilian Merganser is the upper Paran river basin, where the vast majority of the remaining individuals are found. Here, the species inhabits stretches of river with clear, deep pools and riffles and prefers to use submerged logs, overhanging trees, or rocky outcrops for resting and roosting.

The Brazilian Merganser is also found in other river basins within its range, such as the headwaters of the Uruguay and Paraguay rivers, although its populations in these areas are generally much smaller.

Movements and Migration

The Brazilian Merganser is generally highly sedentary and does not undertake extensive migrations or movements. Instead, it tends to stay in or near its established breeding territories year-round.

However, during the non-breeding season, the species may move downstream to quieter stretches of river or more sheltered areas. This may help the birds avoid the higher water flows and unpredictable conditions associated with the breeding season.

Ducks in general are known for their long-distance migrations between breeding and wintering grounds, but not much is known about the migratory habits of the Brazilian Merganser. However, it is likely that the species does not migrate far beyond its established range due to the limited extent of its habitat.

In general, the Brazilian Merganser is a relatively weak flier and prefers to swim rather than fly to get around. This limits the species’ ability to find new habitat or adapt to changes in its environment, making it particularly vulnerable to habitat degradation and destruction.

Conservation efforts for the Brazilian Merganser include habitat protection and restoration, captive breeding programs, and public awareness campaigns to educate local communities about the importance of conserving the species. These efforts are critical to maintaining the Brazilian Merganser’s habitat and ensuring its continued survival in the wild.

Diet and Foraging

The Brazilian Merganser is an adept swimmer and diver, thanks to its streamlined body and long, narrow, serrated bill. The species primarily feeds on fish, spending much of its time underwater hunting for small fish such as tetras, catfish, and characins.


The Brazilian Merganser’s bill is specially adapted for catching fish; it is long and narrow with serrated edges that allow the bird to grasp and hold onto its prey. When hunting for fish, the bird dives underwater and searches for prey using its keen eyesight.

Once it spots a fish, the merganser uses its bill to grab hold of the fish. It then surfaces, swallows the fish whole, and dives back down to continue hunting.


The Brazilian Merganser’s diet is mainly comprised of fish; however, the bird has also been known to feed on aquatic insects and crustaceans. The species prefers to hunt in clear, fast-flowing rivers and streams that offer high concentrations of small fish that it can catch with relative ease.

The merganser’s diet may vary between different regions depending on the availability of prey.

Metabolism and Temperature Regulation

As a cold-blooded animal, the Brazilian Merganser relies on its environment to regulate its body temperature. The species has a relatively low metabolism during periods of low activity, which helps reduce its overall energy needs.

However, during periods of high activity, such as hunting for fish, the bird’s metabolism increases to provide the energy it needs to swim and dive efficiently in search of prey. In colder water temperatures, the Brazilian Merganser’s body may adjust to conserve heat by reducing blood flow to the extremities.

When the bird is not swimming or diving, it will often rest on submerged logs or overhanging vegetation, where it is sheltered from the water’s cooling effects.

Sounds and Vocal


Like many waterfowl, the Brazilian Merganser has a complex system of vocalizations that it uses for communication and social interaction. The species has a variety of calls, including foraging calls, contact calls, and courtship calls.


The Brazilian Merganser’s vocalizations are generally quiet and high-pitched, with a nasal quality. The most commonly heard call is a series of soft, nasal notes that are repeated several times in succession.

This call is often used by the bird to communicate with other members of its flock. During courtship and breeding season, the Brazilian Merganser may produce a more elaborate series of calls.

These calls are often louder and more varied than the bird’s regular contact calls. The male may also perform a series of head-bobbing displays to attract a mate.

Overall, the Brazilian Merganser’s vocalizations provide important clues about the bird’s behavior and social interactions. Understanding the species’ calls and vocal behavior can be an important tool for researchers studying the bird’s ecology and behavior in the wild.

Conservation efforts for the Brazilian Merganser should aim to protect the bird’s habitat, regulate human disturbances, and discourage hunting and persecution. Understanding the species’ diet, foraging behavior, and vocalizations can provide valuable insight into the bird’s ecological requirements, allowing researchers and conservationists to develop effective strategies for conservation and management.


The Brazilian Merganser is a solitary bird that spends much of its time swimming and diving in fast-flowing rivers and streams. The species displays unique locomotion, vocalizations, self-maintenance, agonistic behavior, sexual behavior that are specific to the species.


The Brazilian Merganser is a skilled swimmer and diver, using its wings to swim underwater. Its streamlined body, long, narrow bill, and webbed feet make it an efficient swimmer.

Self Maintenance

Like all birds, the Brazilian Merganser engages in self-maintenance behaviors, such as preening and bathing. Preening is the process of cleaning and caring for its feathers, which is essential for maintaining the bird’s insulation and waterproofing.

The bird will often use its bill to spread oil from a preen gland located on its back to maintain the feathers’ health and appearance. Agonistic


The Brazilian Merganser displays agonistic behavior when defending its territory or resources.

This can include aggressive displays, such as spreading its wings and neck, or chasing off other birds. Sexual


During the breeding season, the Brazilian Merganser engages in a variety of sexual behaviors, including displays of courtship, pair bonding, and mate selection.

Males will often display to attract a mate, performing head-bobbing movements and displaying its bright red bill. Once a pair has formed, the birds engage in synchronized swimming and displays of affection.


The Brazilian Merganser initiates breeding activities in the winter months, which coincides with the onset of the rainy season. The species constructs a nest in a natural hollow, usually an abandoned woodpecker hole or similar crevice, which is lined with feathers or plant material.

The bird lays one to six eggs and incubates them for around 30 days, with both parents taking turns to incubate the eggs. Once the chicks hatch, they will remain in the nest for several weeks, being fed and cared for by both parents.

After the chicks are capable of flight, the family will leave the nest and move to a nearby river.

Demography and Populations

The Brazilian Merganser is considered a critically endangered species, with only around 250 individuals estimated to remain in the wild. The bird’s populations have declined dramatically in recent years due to habitat loss, human disturbance, and persecution.

Efforts are currently underway to protect and conserve the Brazilian Merganser’s remaining habitat. This includes the designation of protected areas, habitat restoration initiatives, and captive breeding programs.

The species’ low population size and fragmented distribution make it particularly vulnerable to stochastic events such as disease outbreaks or natural disasters. Therefore, it is critical that conservation efforts continue to ensure the survival of this beautiful and unique bird.

The Brazilian Merganser is a fascinating and critically endangered species that relies heavily on freshwater habitats, feeds primarily on fish, and displays unique behaviors such as vocalization and agonistic behavior. While the bird’s numbers have declined significantly in recent years, conservation efforts such as habitat restoration and captive breeding programs are underway to protect the remaining individuals.

Understanding the species’ unique behaviors and demands is critical to effectively conserve and manage this iconic bird. By recognizing the importance of this species and protecting it, we preserve not only a fascinating example of avian diversity, but also contribute to balanced ecosystems and sustainable development.

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