Population

Maine’s current population estimate of adult loons is comprised of 1,700 territorial pairs, which is equivalent to 3,400 breeding adults and 700 nonbreeding (but oversummering) subadults and adults. This estimate is based on Maine Audubon’s ongoing monitoring and volunteer efforts in southern Maine coupled with random aerial surveys in northern Maine by the Maine Department of Inland Fisheries and Wildlife in the 1980s.

Seasonal Movements

Loons migrate from their breeding lakes to the ocean in the late fall. Maine’s proximity to the ocean allows loons to remain on their breeding grounds much later into the fall than their midcontinent counterparts. Adults depart before juveniles, thus young birds arrive on the ocean without guidance, prior knowledge, or experience. Band recoveries indicate that the majority of Maine loons overwinter along the coasts of Maine, Massachusetts, New Hampshire, and Rhode Island; however, individuals have been found south of Long Island, New York.

BRI’s Rangeley Lakes study is the longest running monitoring effort of a uniquely color-marked loon population in North America. Shoreline nest placement and the loon’s limited mobility on land make loon nests vulnerable to failure caused by water level fluctuations. Due to this sensitivity, the U.S. Fish and Wildlife Service (USFWS), the Maine Department of Inland Fisheries and Wildlife, and other wildlife agencies identified Common Loons as a species to be monitored in response to the Federal Energy Regulatory Commission (FERC) relicensing requirements for reservoirs.

Overall Study Goals

• Maintain nearly 80 artificial nesting rafts for Common Loons on reservoirs in the Rangeley Lakes region and monitor egg laying rates and hatching success.
• Capture and color-band adult and juvenile loons (373 adults and 111 chicks, for a total of 484 loons from this area have been banded to date).
• Monitor breeding territories on a weekly basis for overall breeding success, site fidelity, and individual performance of uniquely color-banded adult loons.
• Determine local and long-distance movements of breeding loons.
• Develop a long-term baseline for methylmercury availability and monitor the relationship of mercury body burdens and effects of mercury on physiology, behavior, productivity, and survival.

Site Fidelity in Western Maine

More than 200 territorial pairs of loons are annually monitored in the Rangeley Lakes Region. Surveys began in 1993; by the year 2000, the surveys fully covered the area (see figure below).

Researchers have also maintained a major, parallel effort to color band adult and juvenile loons each year. Re-observation of color-banded individuals provides important information about site and pair fidelity, local movements, migratory paths, and wintering areas.

The Federal Energy Regulatory Commission oversees the licensing of dams in the United States and issues new licenses every 20-25 years. The renewal of FERC licenses in the past decade has taken place within the context of negotiated settlement agreements arrived at by the dam licensees, state and federal agencies, and nongovernmental organizations. The International Joint Commission (IJC) plays a similar role to FERC for reservoirs that cross the U.S./Canadian border; Canada does not have a legal entity that corresponds to FERC.

Increased interest in recreational and environmental resources associated with these reservoirs, including breeding loons, has generated new considerations for reservoir management. Fluctuating water levels during the nesting season can have deleterious effects on loon nesting success. Increasing water levels easily inundate nests while lowering water levels strand nests, increasing the difficulty of incubation exchanges and enhancing predation (see figure below).

A study on three lakes in Voyageurs National Park (Rainy, Namakan, and Kabetogama Lakes) during the 1980s found an average of 60 to 70 percent of loon nests failed due to water level fluctuations. Based on a BRI-led study, the IJC in 2000 instituted new water level management guidelines for these water bodies in order to minimize the impact on loon nesting success, which is a good example for similar situations in Maine.

For the past 25 years, the FERC relicensing process has also implemented reservoir management schemes that minimize impacts to nesting loons in the Rangeley Lakes region. The general guidelines recommend maintaining water levels within a 6-inch rise and 12- inch drop during the primary loon nesting period, or the implementation of artificial loon nesting rafts to enhance nesting success.