Conservation and Management

Effects Of Human Activity

Shooting

Accounts indicate overhunting was common at the turn of this century (Phillips 1926). Today, not prized as a game species by hunters. Annual hunting kill estimates for 5 yr blocks (1970–1985) range from 83,100 to 99,100; 64% in the U.S., 36% in Canada; representing 1% and 0.5% of annual Canadian and U.S. waterfowl harvest, respectively (USDI 1988). Since 1999, total harvest averaged 100,388 per year with a higher percentage of total harvest occurring in the US than Canada (89% vs. 11%) than in earlier period (USFWS 2007).

Pesticides And Contaminants

PCB, DDE, and Mercury (Hg) residues have been detected in Hooded Mergansers eggs from a variety of locations in the U.S. (Table 2). Contaminants have not been implicated in female deaths. Although studies consider PCB and DDE concentrations “low,” particularly compared to values for Red-breasted and Common mergansers, there is regional variation, with higher mean values in the northeast, and substantial within-clutch variation (White and Cromartie 1977, Zicus et al. 1988). Hg concentrations approach levels of concern, with means near those identified as harmful in other bird species, and extremes above levels known to cause aberrant behavior in Mallard ducklings (>1 ppm; Heinz 1975, White and Cromartie 1977, Zicus et al. 1988). Also see Breeding: eggs/eggshell thickness.

Habitat Degradation

Populations have suffered on both breeding and wintering grounds from habitat alteration. Early records indicate forestry practices eliminated large cavity-producing trees, altering breeding distributions before 1850 (Phillips 1926). However, aging forests in the east since 1930 may have improved breeding habitats in some areas.

Although acid rain affects a large portion of the eastern breeding area, its impact on populations is uncertain (Longcore et al. 1987, McNicol et al. 1987a, b). Surveys in Ontario indicate mergansers prefer ponds which have low buffering capacity and are thus sensitive to acid precipitation. Low to moderate acidification, however, may improve brood habitat in some lakes by reducing fish populations that compete for invertebrate food resources. Below pH values of 5.5, invertebrate abundance may become so reduced that duckling growth is reduced (McNicol et al. 1987b). Given the extensive breeding areas potentially impacted by acid rain (Longcore et al. 1987), continued monitoring is warranted.

On wintering and breeding areas in the southeast, river channelization, deforestation, and agricultural practices have reduced forested floodplain size and increased sediment loading in many streams, thereby reducing available habitat and possibly lowering foraging efficiency by increasing turbidity. In the Mississippi Alluvial Valley, the increasing number of aquaculture ponds has provided resources for a limited number of birds (Christopher et al. 1988).

Sensitivity To Disturbance

See Breeding: parental care.

Management

To be effective, strategies should be focused over large geographic areas and take several approaches, including managing hunter harvest. Forest management goals should include the establishment and conservation of cavity producing trees (> 100 yr old, > 30 cm diameter at breast height) and the maintenance of riparian forested corridors and forests located within 1 km of suitable brood habitat (Soulliere 1990, LHF). Nest box programs can provide nest sites in otherwise unsuitable habitat; but while valuable as educational and scientific tools, they have limited value for maintaining continental populations. If used, wood or metal boxes with appropriate openings (see nest dimensions) are preferred over plastic buckets (Heusmann and Early 1988, LHF).

Aquatic management goals should include the restoration and/or preservation of water quality and natural hydrology. Sedimentation, chemical runoff from agriculture, acid precipitation, and other pollutants impact food chains and foraging efficiency. In flood plain habitats, maintaining natural hydrologic cycles maintains tree species communities, minimizes tree kill, and favors the proliferation of prey species adapted to historic hydrologic conditions (Fredrickson and Batema 1992). One study found breeding density increased 3-4 years after beaver trapping was stopped on a study plot in Maine, which resulted in increased beaver-created wetlands (McCall et al. 1996).