Movement Studies: Determining Migratory Paths and Mercury Exposure of Eastern Willets Breeding in the Gulf of Maine
Many species of North American shorebirds appear to be suffering significant population declines. Shorebirds face numerous conservation challenges, including anthropogenic disturbance, pollution, predation, and loss of shoreline and wetland habitat through sea-level rise. The exact causes of shorebird population decline are largely unknown but are likely the result of many factors. Determining which factors are currently limiting shorebird populations, and which factors may play a role in the future, is crucial for shorebird conservation.
The Eastern Willet is known to migrate along the coast or over the ocean; however, little is known about its stopover sites and wintering grounds. Conditions at these locations may play a role in limiting willet populations. Through this project, lead by Biodiversity Research Institute and in collaboration with Rachel Carson National Wildlife Refuge and Parker River National Wildlife Refuge, we aim to identify critical stopover and wintering areas throughout the annual cycle of Eastern Willets breeding in the Gulf of Maine.
Project Overview
Since 2011, Biodiversity Research Institute has been deploying light-level geolocator tracking devices on Eastern Willets breeding at Rachel Carson NWR in Wells, Maine, and Parker River NWR in Newburyport, MA. This work is part of a broader effort by the Smithsonian Institute to understand willet movements. The geolocators are mounted to the birds’ legs using colored leg flags; each bird receives a unique color band combination and aluminum band as well. The geolocator remains on the bird and records its location throughout the year, including the remainder of the breeding season, fall migration, winter, and spring migration. When the bird returns to its breeding grounds, it is recaptured and the geolocator removed so the data can be downloaded and analyzed. BRI biologists have also been testing Eastern Willets for mercury contamination, a potential stressor on their wetland breeding grounds and stopover and wintering areas.
Initial Results
By comparing the behavior of the birds captured and tagged in the Gulf of Maine to those studied in New Jersey by collaborators from the New Jersey Nature Conservancy and Smithsonian Migratory Bird Center, we have been able to determine critical stopover and wintering sites for Eastern Willets. Twenty-two of 25 willets nesting in the Gulf of Maine and in New Jersey spent the winter in Maranhao, Brazil, indicating this species may have a very limited wintering range, making these birds even more vulnerable to degradation of those habitats. This information will help conservationists make better decisions for managing and conserving these valuable habitats, such as which lands to protect from development and determining best practices for land management. Our migration and mercury study is ongoing, and there is still much to glean from the data already collected.
Geolocators Help Track Bird Migration
Gaps in our knowledge about migration exist because it has been impossible to track individual birds across thousands of miles. Recently, a new technology has emerged that allows lightweight, inexpensive archival data tags (Global Location Sensing, or GLS tags) to be carried by birds. These devices record a bird’s location as it travels from breeding to wintering grounds, and back. GLS tags sense ambient light levels at a bird’s location to calculate the timing of sunrise, sunset, and day-length. This information is then translated into latitude and longitude.
Because the tags are archival (they store the data they collect and do not transmit it), retrieving the tags requires a second capture of the tagged bird. This means that individuals of the species studied must return to the same exact places in successive years. The willet is a prime candidate for tracking with GLS tags because breeding pairs typically return to the same breeding territories each year.
These tracking efforts will provide a clearer understanding of Eastern Willet ecology and allow for more informed conservation decision making regarding the management and protection of key habitat areas.
Migratory Paths of Eastern Willets Tracked With Geolocators
Since the 2011 breeding season, BRI researchers have been attaching geolocator tracking devices to Eastern Willets captured at Rachel Carson NWR in Wells, Maine, and Parker River NWR in Newburyport, MA. We later recapture the birds and retrieved the archived data from their devices. The data we have recovered from these tracking devices is providing a greater understanding of stopover sites and wintering locations critical to willets throughout their annual cycle, the migrations paths these birds take, and the timing of their movements. This information is critical for developing effective plans for managing and conserving valuable habitats for this species.
Shown are (left) the migration routes and stopover sites over one year of an Eastern Willet tagged at Parker River NWR, and (right) the movements over two years of an Eastern Willet tagged at Rachel Carson NWR.
