Common Merganser

Common Mergansers are a common nesting duck on New Hampshire’s Lakes & Rivers, and also winter in the state wherever there is sufficient open water. Their bills are uniquely adapted to a diet of fish, being long and thin with serrations to facilitate a firm grip on their prey. If you watch mergansers foraging, you’ll see them dipping their heads into the water as they swim, and when fish are sighted the bird will make a slight leap forward before plunging into the water in pursuit. If there are large schools of fish in an area, you might see several mergansers hunting in a flock and diving somewhat synchronously.

Common Mergansers are cavity nesters, and use large hollow trees and nest boxes along more secluded sections of lake and river shores. When the chicks hatch, the whole family will head to the water, and if a female is followed by 20 or more ducklings it is generally the result of broods mixing up after they’ve left the nest.

Like most waterfowl, Common Mergansers are increasing in New Hampshire and the Northeast. The ups and downs in the Christmas Bird Count data are probably based on the extent of open water, but the highs have been much higher in recent years than they were in the 1970s and 1980s. This could also be attributed to warmer winters and thus less ice, so the Breeding Bird Survey trend is probably a more appropriate matric for assessing population trend.

Increasing merganser populations are believed to be a result of improved water quality, especially declines in chemicals like DDT. As fish-eating birds, mergansers were impacted in the same manner as eagles, pelicans, and other “poster species” of the DDT era, and conservation efforts targeting those more charismatic birds have benefited other species in the same ecosystems. At the same time, other contaminants still threaten mergansers, including mercury, lead, and organic chemicals like PCBs. Mergansers also suffered from reduced prey ability at the height of the acid rain era, when lakes became increasingly inhospitable for many species of fish. Thankfully, the days of DDT are over and acid rain is less of a problem for aquatic habitats than it used to be, and Common Mergansers have recovered nicely over most of their range.