New York Natural Heritage Program
Common Loon
Gavia immer (Brunnich, 1764)

Threats [-]
Although the population of breeding loons in New York is stable or slightly increasing, several threats are currently acting in combination to negatively affect loons in New York State. Mercury poisoning is one of the most significant threats. Elemental mercury released from sources such as waste incinerators and coal-fired power plants mostly in the Midwest is deposited by atmospheric currents and is transformed in water bodies into methylmercury, a neurotoxin. Common Loons are particularly affected by this process because they are predators at the top of a long aquatic food chain. In loons, high mercury levels are correlated with behavioral changes that lead to lowered reproductive success, decreased survival, and increased susceptibility to other diseases. Preliminary results indicate that 25% of loons sampled in the central Adirondacks had mercury levels high enough to result in behavioral changes and/or decreased reproductive success, and the Adirondacks are considered a biological mercury hotspot (Evers et al. 2007). In addition, lake acidification increases the availability of methylmercury and also leads to a decrease in the diversity and abundance of prey for loons in affected water bodies (Schoch and Evers 2002). Ingestion of lead fishing tackle causes lead poisoning and eventually death, and ingestion of fish hooks and entanglement in fishing line can also cause permanent injury or death. Of 105 Common Loons found dead or debilitated in New York from 1972-1999, 21% of the pathologies were attributed to ingestion of lead fishing weights, while 23% had aspergillosis (Stone and Okoniewski 2001). Oil spills pose a threat for loons that are migrating or that are on their wintering grounds along the Atlantic coast. Loons are also susceptible to human disturbances at breeding lakes. These include effects of shoreline development, which may reduce the suitability of lakes for nesting, and disturbances caused by paddlers, campers, boaters, and jet-skiers, which can interrupt incubation and result in nest failure or abandonment. Loon nests may be affected by water fluctuations as well, which may flood nests or leave nests more vulnerable to predation. Illegal shooting along the Atlantic coast and elsewhere is a known mortality factor. Increasing numbers of predators such as raccoons, otters, and eagles could also pose a threat. Common Loons are also susceptible to several diseases including type C and type E botulism. Since 2000, an outbreak of Type E botulism, Clostridium botulinum, has occurred annually on Lake Erie. Outbreaks on Lake Ontario were documented beginning in 2002. These outbreaks are apparently killing migrating loons (over 10,500 birds from 2000-2005) mostly from the eastern Canadian Provinces and the upper Midwest because Adirondack loons appear to migrate directly to offshore wintering areas along the coast of Rhode Island, Massachusetts, and New Jersey (Kenow et al. 2006).

Conservation Strategies and Management Practices [-]
Common Loons can adapt to moderate levels of lakeshore development and recreational use, but it is important to minimize disturbance to nesting loons (Spillman 2006). Disturbed incubating loons may not return to their nests for an hour or more, leaving eggs vulnerable to predation and cooling (McIntyre 1975, Titus and VanDruff 1981). Nesting areas should be located and protected. Small islands (those less than 5 ha) and deadwaters should not be developed at all, and buffer zones of 150 m should be left undisturbed on either side of mainland nest sites and deadwater entrances (Strong and Bissonette 1985). Nursery areas of lakes (shallow areas and coves where adults raise and collect food for their chicks) should also not be disturbed. Jet skis currently are the most threatening disturbance to chicks because they are fast, highly maneuverable, and able to run in shallow water where loon nests and nurseries are often located (McIntyre and Barr 1997). Motorboats may affect loons more negatively than canoes. Boat engine horsepower should be limited and speed limits should be established on smaller breeding lakes or in designated areas of larger lakes. Loons defending their territories through behaviors such as the penguin dance or vocalizations such as the tremolo (laughing call) should be given their space. Non-lead sinkers and jigs should always be used when fishing, and snagged tackle should be recovered. Human-caused water level fluctuations should be minimized, especially during the peak nesting period of mid-May to mid-July, as nests can be lost to inundation or increased exposure to predators from drawdown. Rises in water levels are more detrimental than drawdowns, especially when they occur late in the season when the loons have little possibility of re-nesting (Strong and Bissonette 1985). In the Adirondacks, excellent natural nesting sites are available, and these are preferred over artificial nest rafts, but artificial rafts may improve nesting success under certain conditions (e.g., lakes with a breeding history experiencing fluctuating water levels and recent repeated failed nesting attempts). Information regarding raft construction design and placement recommendations can be obtained from the North American Loon Fund (McIntyre and Barr 1997).

Research Needs [-]
Considerable research has been conducted on the Common Loon, as it is an iconic species and excellent indicator of trends in environmental quality. Current research is focused on detecting population trends, effects of mercury pollution on reproductive success, and use of migratory routes and wintering areas. These efforts should be continued in order to gather information on the long-term effects of acidification, environmental pollutants, and human interactions. Population monitoring and contaminant research is being coordinated with other efforts in the Northeast to enable an assessment of the effects of mercury and other factors on northeastern loon populations. Continuing such monitoring efforts will enable the early detection of unusual changes in population levels and the implementation of appropriate management efforts as well as assist in the development of appropriate policies regarding mercury and other contaminants (Schoch and Evers 2002). The mechanism of the type E botulism outbreaks affecting migrating loons on the Great Lakes is still poorly understood, and additional research is needed to determine the causes of the outbreaks, and how they can be prevented or minimized (Schoch 2002). Further study is also needed on the sensitivity of loons to toxins (McIntyre and Barr 1997), ecology of wintering loons (Rimmer 1992), and life history of juveniles between the time they fledge and return to northern lakes (Holst 2005). The inexperienced juveniles apparently do not migrate with the adults and require suitable stopover waterbodies on their way to the coast.