Ecology and Vulnerability

Willet

Background
In the eastern US, the willet is a shorebird that breeds in coastal regions from the Canadian Maritimes to the Caribbean. Eastern willets spend winters in coastal areas of the southern US and northern South America. In Massachusetts, willets are clustered at Monomoy, Plum Island, and Parker River National Wildlife Refuges ⁶, but the birds can migrate. Willets breed in coastal salt marshes, barrier islands, barrier beaches, ocean-side short grass meadows, and shallow puddles and salt pans with cordgrass (Spartina patens and S. alterniflora) ^1,2,6. The birds feed in oyster beds, mudflats, sparsely vegetated salt-marsh habitats, beaches, and along tidal creeks where they consume insects, small crustaceans, mollusks, polychaetes (marine worms), and even small fish6. Willets nest in smooth cordgrass, salt hay grass, or on beach debris in the high marsh; however, the invasive Phragmites australis that invades and replaces salt marsh grasses does not provide adequate nesting habitat ^1,6.

Breeding Bird Survey (BBS) data show an overall decrease in the willet population of 1.9% annually across the eastern region, but no statistically significant trends for the species in Massachusetts ⁸. Threats to eastern willets include habitat loss due to development on breeding grounds, stopover sites, and wintering areas; contaminants that accumulate in coastal sediments; and reduction in habitat quality through draining and impounding of salt marshes and mosquito ditching ^1,6. Willets appear to be less abundant in small habitat patches, and may be sensitive to habitat fragmentation ².  The willet was recently added to the US Fish & Wildlife Service conservation watch list as a species requiring management attention.

Climate Impacts
Climate change is likely to adversely affect willet habitat. The coastal habitats that the willet relies on may be reduced as sea level rises and interacts with nearshore development ^5,11. This species could also be particularly sensitive to sea level rise because nest success is linked to flooding ⁶. A study conducted in Chesapeake Bay found that willets could experience population declines of nearly 80% with a sea level rise of 3.3-6.6 ft by 2100 ¹³. Moreover, the coastal armoring aimed at mitigating sea level rise can also reduce willet abundance and the abundance of their macroinvertebrate prey ⁴.  Some tidal flats and salt marsh habitats are projected to increase with climate change, which may benefit some shorebirds ⁹; however, changes in hydrology and streamflow from land use change and climate change may reduce the sediment and organic matter that some salt marshes receive making them unable to keep up with rates of sea level rise ⁷. In addition to direct habitat loss from this, changes in precipitation and increased temperatures could lead to salt accumulation in soils and less productive habitat, ultimately resulting in reductions in suitable bird habitat ¹². These effects can be worsened by the nutrient enrichment that often accompanies development and can eventually cause habitat shifts ¹².

Drastic fluctuations in annual precipitation can  also interact with development in upland habitats to impact coastal waterbirds ¹⁰.  In addition, increasing frequency and intensity of coastal storms and surges could negatively impact shorebirds, but they could also create new habitat ³. The more intense hurricanes expected due to climate change could disturb foraging and nesting habitat for shore and marsh birds, which can have both negative and positive effects ¹². Finally, in addition to affecting habitat availability, climate change can also shift the abundance and distribution of prey species, as well as the timing of prey availability.