Ecology and Vulnerability

Wood Duck

Background
The wood duck is one of the least migratory of North American ducks. Most of its wintering and breeding range is within the contiguous US.  Populations south of North Carolina, Tennessee, and Little Rock, Arkansas are nonmigratory and supplemented in winters by an influx of migrants from the north.  Further north is a narrow geographic band in which wood ducks are quasimigratory, meaning that they stay during mild winters and migrate in severe winters.  In the far north of the range, the majority of breeding wood ducks are migratory¹.  In Massachusetts, some wood ducks are year-round residents, though the majority migrate south during the winter².  Wood ducks are a forest-adapted species that nest in hollowed cavities, usually found in trees of at least 16 inches in diameter³.  Wood ducks carry out their annual cycle in a forested wetland complex that includes a mixture of habitats such as live forest, rivers, oxbows, riparian corridors, beaver ponds, shrub-scrub, and robust emergent vegetation⁴.

Climate Impacts
In northern populations, environmental conditions and the energetic costs and dangers of longer migrations may result in a greater number of young females delaying the timing of when they first breed.  In South Carolina, 28% of females were found to delay or defer breeding until after the first year of life; in Massachusetts, 52% deferred breeding⁵.  In South Carolina, deferred breeding was associated with decreased survival.  Additionally, in years with harsh winter conditions, young wood ducks will migrate greater distances than older ducks, potentially increasing the percentage of the population that defers breeding^5,6.  These findings suggest that the severeness of the winter can have implications for population dynamics, and that milder winters in Massachusetts may be favorable for wood ducks.  Because there appears to be latitudinal (north-south) variation in how much of the population migrates, milder winters could increase the number of year-round residents in Massachusetts.  Climate scenarios for the northeast predict an increase in short-term drought conditions, reduced summer stream flows, and a longer duration of low summer stream flows⁷, with a potential reduction in habitat for wood ducks. 

How all these factors will interact is unclear; however, modeling studies by the University of Massachusetts suggest that milder temperatures will overall be favorable to wood duck populations in the Northeast⁸.