The U.S. Fish and Wildlife Service designated the Red-throated Loon as a “bird of conservation concern” due to an overall declining population; however, some populations appear to be stable and others have unknown trends. Primary population threats include nest predation, oil spills, contaminant exposure, overfishing of forage fish, and mortality associated with entanglement in fisheries gill nets. Additionally, it has been ranked as a species that is highly sensitive to displacement from foraging areas near offshore wind energy facilities.

In order to assess the effects of disturbance and the potential population impacts of offshore wind development on Red-throated Loons, basic information must be collected on their distribution and behavior, including flight pathways and timing of habitat use, within proposed wind energy areas. BRI is working with multiple collaborators to meet those objectives by determining fine-scale occurrence and local movement patterns of Red-throated Loons in federal waters of the mid-Atlantic U.S. during migration and winter, using platform terminal transmitter satellite tracking tags (PTTs).

Red-throated Loons are targeted for capture between January and March within Delaware Bay, Chesapeake Bay, and Pamlico Sound, and within 3 to 4 miles offshore in the Atlantic Ocean adjacent to those bays. Individual birds are captured at sea with large handheld dip nets while using established night-lighting techniques. Overall health assessments of birds are conducted by wildlife veterinarians who then surgically implant PTTs before releasing the birds at their capture locations. Satellite transmitters send location data of individuals to orbiting satellites during set periods of the day, which can then be mapped. Tracking individuals will be used to identify high use areas during winter and migratory periods, including important offshore migration corridors and source breeding populations. Additional opportunistic research topics being examined during this study include general health assessment findings, contaminant exposure risk, and genetic profiles of Red-throated Loons wintering on the East Coast.

Capture efforts conducted in 2012, 2013, and 2014 resulted in the deployment of 66 satellite-tagged Red-throated Loons. Tracking results to date have yielded critical and previously unknown information regarding the species’ winter habitat use, migration routes, and breeding locations. Birds typically left the wintering grounds within the first two weeks of April with most following a northward route along the East Coast while utilizing major stopping and staging areas, particularly Nantucket Sound, Gulf of St. Lawrence, and Hudson Bay. Arrival on the breeding grounds typically occurred within the first two weeks of June ranging primarily across Nunavut north to 80 degrees, but also northwestern Greenland, northern Quebec, and as far west as Banks Island, Northwest Territories. Southward fall migrations typically began in late August and tended to follow a more inland route that relied on the southern Great Lakes as a major staging area before arriving back on the wintering ground in late November and early December.

Additional funding provided by the Bureau of Ocean Energy Management for a fourth field season beginning in winter 2015 will extend what was initially a 3-year study, which will serve to strengthen the study by increasing the overall sample size, and testing alternate tagging techniques designed to increase tag life and reduce invasiveness over implanted PTTs