Breeding Bird Atlas 2 Results

See all of the BBA2 data to date on the USGS BBA Explorer.

Preliminary Results:
Common & Hooded Mergansers: Increasing

Hooded Merganser
Latin name: Lophodytes cucullatus
Breeding Habitat: Wooded freshwater wetlands
Massachusetts Status: Increasing

Common Merganser
Latin name: Mergus merganser
Breeding Habitat: Wooded freshwater wetlands
Massachusetts Status: Increasing

Note: We haven't included the Red-breasted Merganser here, as it has always been rare for them to breed in Massachusetts — this is the very southern end of their range.

Hooded Merganser
This fetching bird has long bred in the state of Massachusetts. But when the European colonists felled the trees it nested in, the Hooded Merganser retreated to those few wooded wetlands in the heart of the state to await a more auspicious climate. That climate, it would seem, has come. Hooded Merganser suffered many of the same pressures as Wood Ducks. Both are cavity-nesting waterfowl that depend on wooded freshwater wetlands to breed and raise their families. As these habitats disappeared throughout the state, the Hooded Merganser disappeared with them.

As any hunter can tell you, however, Mergansers have one big advantage over Wood Ducks: they taste terrible! A diet of fish and marine invertebrates makes Merganser flesh oily and odorous, so the Hooded Merganser was spared the extreme hunting pressure that nearly extirpated Wood Duck from Massachusetts. As of Atlas 1, breeding Hooded Merganser was concentrated mostly in the central part of the state.

Hooded Merganser has also benefited from Wood Duck conservation. The programs put in place to protect Wood Duck territory and create Wood Duck nest boxes work just as well for Hooded Mergansers. In fact, these two species will often lay eggs in each others’ nests, and because their eggs have the same incubation time, the young all hatch together and are raised by the mother of one species. These “mixed broods” actually have a fairly decent chance for survival. With Massachusetts reforesting and beaver-created wetlands proliferating, it should come as no surprise that Hooded Merganser’s star is rising as of Atlas 2.

Hooded Merganser has consolidated its position in Worcester, Franklin, and Hampshire Counties. Berkshire County now has a decent number of confirmed breeders as well, and Hooded Merganser is creeping into western Middlesex County. A few hotspots in Essex and Plymouth Counties will likely be good populations to watch as the Atlas moves forward. Hooded Mergansers are secretive breeders, though, so it takes patience and diligence to search them out!

Common Merganser
Common Mergansers are extremely hardy and are among the last to leave fresh water as it begins to freeze over. This species is believed to have bred throughout the state prior to 1900, when it began to disappear. The why’s and how’s of this species’ population trends are instructive.

Like Hooded Mergansers, Common Mergansers prefer to nest in cavities near water. Also like Hooded Mergansers, they dine mainly on fish. Unlike Hooded Mergansers, however, they prefer to raise their young in the open water of wide rivers and large lakes. They therefore tend to be somewhat easier to find and document when breeding than Hooded Mergansers are. Add to this the fact that they are even less frequently shot than Hooded Mergansers are (they don’t look as handsome above the mantle, and they taste just as bad), and you would expect to find a fairly respectable population of Common Merganser in Atlas 1.

Well, perhaps not. The Common Mergansers’ preference for wide rivers and open lakes means that they often take the brunt of whatever chemicals run off into the water supply. Pesticides and industrial waste accumulate in small fish, which are eaten by big fish, which are eaten by mergansers. The concentration of chemicals is magnified in the fatty tissue of top predators like mergansers, and it often harms their reproductive success. Likewise, wide open bodies of water are particularly susceptible to acid rain caused by air pollution, and the fish kills that result from acidification of water bodies deprive mergansers of food. Fortunately, Massachusetts has come a long way since the 1970s.

Stricter controls on emissions and pesticide use have done wonders for water quality, and it seems that the Common Merganser may have gone along for the ride.  The nest box programs that were so beneficial to Wood Duck and Hooded Merganser were also helpful to Common Merganser, as large snags became increasingly difficult to find.  The final piece of the puzzle, as it is for many species of waterfowl, is beaver.  The Common Merganser’s recent increase in numbers is concentrated in western Franklin and Hampshire Counties, which have also seen great recovery in their beaver populations.       

Breeding Population Changes Between BBA1 and BBA2