The Common Loon (Gavia immer) is a piscivorous water bird found across the northeast United States and throughout Canada during their breeding season. They winter on the U.S. coast in Massachusetts, New Hampshire and Maine as well as more southerly into Mexico. Common Loons are piscivores meaning they feed mainly on fish, such as sunfish and perch. When fish are scarce, they will feed on snails, crabs, amphibians and invertebrate larvae. They have bodies that are perfectly adapted for diving. Their legs are set far back on their body to help them propel themselves underwater. This trait, however, makes it difficult for them to walk on land. To compensate, they build their nests along the shorelines of lakes with a steep drop-off to allow them to slip into the water with ease. Loons need about 3-4 meters of water clarity to find fish, so they need clear water conditions to thrive. They typically require lake sizes of about 20 hectares or larger per breeding pair. If resources are poor in a particular lake, they may require a minimum lake size of 40 ha. Larger lakes may support more than one pair of loons, but if a lake is 80 ha or under it typically can only support one breeding pair. Loons are serially monogamous and have multiple partners throughout their lives. Loons are more faithful to their territory than they are to other loons. The nesting season begins in May and continues into July. Both partners participate in nest building along the shoreline of lakes with site selection usually driven by males. Females will lay one or two eggs per clutch which are incubated by both the male and female for 26-31 days. The semi-precocial chicks will hatch and leave the nest within a day and begin to ride on the backs of their parents for up to 2 weeks. The chicks are fed by adults until they are fully developed at around 11 weeks (Tischler 2011).
Loons face a variety of issues and threats at all life stages, which can differ greatly. Threats facing loon chicks include intraspecific aggression, trauma, and abandonment. Competition among chicks may result in siblicide often by the dominant or first-born chick. Nest-abandonment may occur if territory takeover occurs during chick-rearing. Disputes over territory among adults often result in chick fatalities, which involve loons from other territories invading the territory of the resident loon. Male intruders will often kill chicks of the invaded territory. Death in immature loons is often the result of fungal respiratory disease and trauma. Juveniles will retreat into nearshore areas during territory disputes to avoid injury by adults. Adults face issues such as infection, trauma, lead toxicosis and other anthropogenic factors. Wintering adults were observed to have much poorer body conditions than breeding adults and are more likely to suffer from infection. The high energy requirements for winter molt result in higher metabolic stress, leading to the increased like hood of infection and disease. Breeding adults face lead toxicosis by ingesting contaminated fish. Half of adult loon mortality has been observed as a result of mainly anthropogenic threats (Sidor 2000).
Natural threats focusing mainly on adult loons include intraspecific aggression, trauma, lead toxicosis, oil spill contamination, fishing line entanglement, gunshot wounds, respiratory and other infections and emaciation. Many of which are anthropogenic (human-caused) threats. Intraspecific aggression stems from territory disputes. Loons are notoriously territorial and will defend their area from invading birds, often resulting in mortality. Lead toxicosis occurs when a bird ingests a fishing weight. Studies have shown that loons who suffered from lead toxicosis resulting in mortality had relatively high body weights, while other studies showed that these individuals had more poor body conditions (Daoust, et al. 1998). It has been indicated that weight loss is not always seen is birds suffering from toxicosis, and other natural factors may come into play when observing their body conditions. Mortality from lead toxicosis was recorded as almost twice as common in New England compared to populations residing in Canada. Loons afflicted by gunshot wounds usually did not perish from the gunshot directly, but as a result of infection from the wound, which would impair the birds foraging ability resulting in mortality from infection or emaciation. Deaths resulting in parasitic infections were determined by the presence of nematodes, cestodes or trematodes. This method of mortality was most common in immature loons.
Many of these threats have changed over time. Historically, loons were shot and killed due to them being a threat to game fish. This has become less of a regular occurrence and less loons are killed presently as a result of gunshot wounds than were killed in the early 1900’s. Other more historical threats such as DDT have also almost been eradicated. However, newer threats such as acid rain and oil spills pose new issues for this species. If a couple of management strategies were put into place, it could have a significantly positive impact on the populations of this species. A few strategies proposed by the U.S. Fish & Wildlife Service include; water level management (involves the creation of reservoirs that keep the water level ideal for loons to ensure sustainability), artificial nest platforms and avian guards (the construction of floating rafts that allow for nesting in areas where shorelines have been degraded. The implementation of guards would allow for less exposure to egg predators and lessen the visibility to the nests), and signs, buoys and roping. Though not very invasive, these strategies could aid in the increase of the common loon population. More involved methods of conservation policies have been put forth in addition. These includes bans on lead in fishing tackle (effective January 2000), habitat protection (protecting areas where loons breed), monitoring, research, and education (Evers 2007).
Maintaining the population of the common loon is the primary goal of these conservation tactics. Research is one of the most effective methods of preserving this species, as keeping up to date with the ecology behind what makes loons successful is essential for coming up with new policies to protect them. Informing the public will also be useful, if we can get more people to care about these birds the easier it will be for us to conserve them and to get the public to want to do the same.
Borden, Sally E. et al. Vermont Common Loon Recovery Plan. Vermont Fish & Wildlife Department. 15 September 1998.
Evers, David. STATUS ASSESSMENT AND CONSERVATION PLAN FOR THE COMMONLOON (GAVIA IMMER) IN NORTH AMERICA: 2007. United States Fish & Wildlife Service. 2007.
Sidore, Inga F. Mortality of the Common Loon in New England, 1987 to 2000. Loon Preservation Committee. 1987-2000.
Strong, Paul. “The Suitability of the Common Loon as an Indicator Species”. United States Department of Agriculture. 1990
Tischler, Keren B. Species Conservation Assessment for the Common Loon (Gavia immer) in the Upper Great Lakes. USDA Forest Service. September 2011.