Brazilian Merganser

The Brazilian Merganser (Mergus octosetaceus) is one of the most threatened waterfowl in the world and one of the most threatened birds in Americas. Its distribution is restricted to the center-south of Brazil, and parts of Paraguay and Argentina. The species inhabits clean rivers and streams, with rapids and still waters, bordered by forests and with fish abundance. Besides being naturally rare, it has been affected by several human activities that interfere directly or indirectly with its habitats. Until very recently, there was very little available information about Brazilian Merganser. Fortunately, in the last years, intense field studies have improved our knowledge about its habits, ecology and distribution. The information which has been arisen from these studies, although still basic, is helping the species conservation.

In 2006, the Brazilian Ministry of Environment (MMA) published the Action plan for the Brazilian Merganser Conservation, a strategic document with guidelines for conservation actions in long term.
In 2008, the Instituto Terra Brasilis started a project to mark and monitor Brazilian Merganser individuals using colour rings and radio transmitters in the Serra da Canastra region, state of Minas Gerais. We believe the coming results will lead to a major contribution to improve our knowledge about this species, in particular in its territoriality, migration and dispersal.

## Distribution

The Brazilian Merganser formerly was widespread in south central Brazil and in adjacent regions of Argentina and Paraguay (see Historical Changes). Currently the distribution is much more restricted. A few recent sightings confirm this species still survives in Argentina and Paraguay (Giraudo and Povedano 2003). Although the situation of the species is extremely critical, some researchers believe that sizable overall populations may still exist in the extensive river systems of Misiones (Giraudo and Povedano 2003). In recent decades, the species was reported from only a few localities in Brazil, most of them in protected areas and their surroundings, such as the Chapada dos Veadeiros National Park (Collar et al. 1992), Serra da Canastra National Park (Lamas 2006, Silveira and Bartmann 2001) and Jalapão State Park (Braz et al. 2003). Its occurrence was registered in the west of the state of Bahia (Pineschi and Yamashita 1999), although subsequent surveys failed to confirm the species in that region (Silveira 2008). One individual was recently observed for a few weeks in the Itacolomi State Park, in Minas Gerais State (De Paula et al. 2008) but it seems to be an occasional occurrence since no other individual was found in that region. Recent surveys also have failed to confirm its occurrence in the state of Paraná (Louri Klemann Júnior, pers. comm., 2007). In 2008, three individuals were observed in Patrocínio municipality, in the western part of the state of Minas Gerais, thus confirming its actual occurrence after 30 years of the first report in that locality (unpublished data). In summary, currently in Brazil, the Brazilian Merganser populations seem to be concentrated in a few localities in the states of Minas Gerais, Goiás and Tocantins.

## Diet

Brazilian Mergansers feed basically on small fish they capture during dives, although aquatic macroinvertebrates also contribute to their diet. Very often, before diving, they search for their prey swimming with just their heads submerged. Dives can last 15 to 20 seconds (Hughes et al. 2006), and even 30 seconds in deeper pools. We have observed them catching insects flying around their heads. In the Serra da Canastra region, the most common fish species which serve as their food are “lambaris” (Astyanax spp.) and “barrigudinho” (Phalloceros caudimaculatus). Stomach content analysis of individuals from Misiones, Argentina, showed they ate lambaris, ciclids, catfish, “virolito”, larvae of Dobson flies and, probably, molluscs .

## Behavior

The species spends the days interspersing foraging and resting periods. Generally, they rest on rocks or branches which are projected out of water, as well as on river beaches. They also can stay in the water motionless or with very slow movements. They remain always alert. In any sign of danger, they immediately go into the water. Being in the water, depending on the risk, they either swim quickly down or up stream, or take off flying away. Most of the times, they fly close to water, following the water course; nevertheless they can also fly higher (about 20 m high). For long distance movements the flights can be even higher, always following the water course. The adults never fly when they have flightless young. In this case, the family attempt to escape by taking cover in vegetation along the shore vegetation, or swimming quickly away. The parents maintain the young between them when swimming and they constantly keep guard over the offspring. Brazilian Merganser is a proficient swimmer and even the young easily pass through strong rapids. There is indication the total moult occurs soon after the reproductive season, as it happens with other mergansers, but this requires confirmation. bruh.

## Territoriality

We believe Brazilian Merganser do not migrate seasonally between different regions, basins or sub-basins. In the rainy season, when the water turns into muddy, it shows a preference for upper streams where the small tributaries are clear. In this period, the birds are more difficult to observe. The couples keep their territories well defended all over the year. Although territorial disputes have been recorded, fights between pairs established in adjacent territories are rare. Recently, we have observed some Brazilian Merganser pairs in territories we believed already to be occupied by a different pair. Hopefully the results from the project of marking and monitoring, still in developing, will clarify these issues on territory overlap.

## Sexual Behavior

Brazilian Merganser is monogamous. The same pair seem to live together for a long time, if not throughout their lives. However, since their individual identification is very difficult, only with the advance of the marking-monitoring project (Lins et al., in press), will we be able to confirm whether the couples we observed year after year are really composed by the same individuals. Males court females on the water; the copulation is also on the water. When the female is ready to accept the male, she lowers her head and extends the body horizontally. Then the male mounts the female grasping her crest with the beak. The copulation can last for 15-25 seconds, notably longer than in other mergansers (Silveira and Bartmann 2001).

### **Breeding**

Brazilian Mergansers nest in holes of trees, and holes in rocks and in river banks (Lamas and Santos 2004, Partridge 1956, Andrade et al. in press). The entrance to the nest cavity is located from 2 to 25 m above the water. Only the female incubates, and she leaves the nest twice per day to feed (Bruno et al., in press). The male spends most time resting or feeding nearby, constantly vigilant, but sometimes flies off, departing the area for several hours. The female lays up to eight eggs, which are incubated for about 34 days (Bruno et al., in press). The eggs are oval in shape and pale beige, almost white, in coloration. The following mean measures data were taken from one nest with seven eggs: 61.7 mm (length), 42.5 mm (width) and 59.86 g (weight) (Lamas and Santos 2004). When leaving the nest, the female covers the eggs with her down feathers.

The ducklings leave the nest in the following day after hatching (Bruno et al., in press). The ducklings are encouraged to abandon the nest by the mother´s call. The family stays together all the time; the parents constantly keep the young between them. The parents provide the ducklings with fishes and invertebrates. They feed their young directly into their beaks, or they place caught fish in the water after shaking it in order the ducklings can catch it. After 10 days of life, young were observed fishing on their own, reducing the need for food provided by their parents (Bruno et al., in press). The young are able to perform short flies when they are around 2 months old (Renata D. Andrade, pers. comm.). They generally stay with their parents about six months. However, after monitoring marked birds, we have been observed that some offspring stay longer with their parents, up to 8 or 10 months (Lívia V. Lins, pers. obs.). Many young die in these first months of life.

## Social and Interspecific Behavior

There is very little information on the interspecific interactions and their consequences for the Brazilian Merganser populations. Some other bird species commonly observed in the vicinity of the Brazilian Merganser are kingfishers , Brazilian Teal, Pied-billed Grebe, Anhinga and Muscovy Duck. Nevertheless, there is no evidence of direct interaction between these species and the merganser. The Neotropical River Otter also is commonly seen in rivers where the Brazilian Merganser occus. It may compete with Brazilian Merganser for the same food resources since both diets are based on fishes. It is also important to evaluate the probability of predation on Brazilian Merganser by the otter.

## Predation

Little information. It has been speculated that other mammals and birds recorded in the Serra da Canastra region, based on their diet, size and habitat, might prey on Brazilian Merganser (Lamas and Santos 2004). Among mammals, pumas, ocelots, margays, jaguarundis, maned wolves, crab-eating foxes, tayra and Neotropical river otters as potential predators on Brazilian Merganser. Among raptors, Dante buzzetti highlights black-chested buzzard-eagle, crowned eagle, Aplomado falcon, grey-headed kite,  black and White Hawk-Eagle, collared forest-falcon and Great Horned Owl as potential predators.

L. V. Lins and colleagues (pers. obs., 2007) have observed a Great Black Hawk (Buteogallus urubitinga) stooping over a merganser in Serra da Canastra. The merganser evaded capture by diving under the water each time the hawk got close. Partridge (1956) also drew attention to the Black-and-white Hawk-Eagle as amongst the most dangerous predators of Mergus octosetaceus in Argentina. The same author highligthed the “Dourado” (Salminus maxillosus), one of the most voracious fish of the upper Paraná, as a potential enemy to young ducklings of any species. We saw dogs turning excited after hearing Brazilian Merganser play-back vocalizations. This may be evidence of a possible agonistic interaction between the two species.