Ecology and Vulnerability

Louisiana Waterthrush

Background
The Louisiana waterthrush is the only obligate riparian songbird that breeds in the eastern United States¹, which means that they are strongly associated with unpolluted, headwater streams and associated wetlands occurring in contiguous forest².  In these habitats, they feed preferentially on aquatic macroinvertebrates³, but will also forage for arthropods (like insects)⁴.  Their habitat requirements mean that they are good bioindicators of stressors on forested headwater streams where a lack of waterthrush could indicate a stressed habitat¹.  Louisiana waterthrushes breed in the eastern United States from Wisconsin to New England and south to Florida, overwintering in the Caribbean and Central America⁴.  Although the species is found across Massachusetts, they are concentrated in the western half of the state, particularly the Berkshire Transition region⁵.

Climate Impacts
Climate projections for the Northeast indicate that higher temperatures and a longer growing season will result in increased evapotranspiration (the loss of water by evaporation from soil and transpiration from plants)⁶.  These changes are likely to result in increased short-term drought conditions⁶. As noted above, Louisiana waterthrush are dependent on riparian habitat (river banks and associated wetlands) and a significant portion of their diet comes from foraging in muddy, saturated soils⁴.  Drought conditions may reduce the availability of saturated soils, and have the potential to reduce the availability of suitable habitat.  In addition, one study found that daily nest survival for waterthrushes was highest when rainfall was at intermediate levels⁷.  This study concluded that extended periods of drought would have negative consequences for reproduction.

However, Massachusetts is located at the northern extent of the range of the Louisiana waterthrush.  Distributions are expected to move north for many bird species⁸, possibly shifting Massachusetts nearer to the center of the breeding distribution.  Modeling studies conducted by the University of Massachusetts project an increase (by nearly 25%) in the capability of the landscape of the Northeast to support this species by 2080⁹.