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.