The hooded merganser is a sexually dimorphic species. They are also preyed upon by the common merganser and the blue heron. This duck was similar in size to the red-breasted merganser. The Brazilian merganser ("Mergus octosetaceus") is a South American diving duck in the Mergus genus. The Auckland Island merganser "Mergus australis" went extinct in 1902. The hooded merganser is a diving predator that largely hunts by sight while under water. The red-breasted merganser ("Mergus serrator") is a diving duck, one of the sawbills. Endangered birds include Brazilian merganser ("Mergus octosetaceus") and yellow-bellied seedeater ("Sporophila nigricollis"). The adult red-breasted merganser is long with a wingspan. The hooded merganser, often termed "Mergus cucullatus", is not of this genus but closely related. The hooded merganser has a sawbill but is not classified as a typical merganser. The common merganser eats fish and nests in holes in trees. Along with the smew and hooded merganser, they are therefore often known as "sawbills". Winter ecology and conservation threats to the scaly-sided merganser were reported in 2012. Another threat to the Brazilian merganser is tourism.