Common loons nest each year on Chester Morse Lake. They migrate to Puget Sound and other areas of the Pacific coast to spend the winter.
In Washington state, common loons (Gavia immer) can be found foraging or resting during migration on several lakes, but nest on only a few lakes and reservoirs. The number of confirmed loon nests in western Washington varied from eight to 10 each year between 1990 and 1999.
Two to three nest sites are on Chester Morse Lake. (Another pair nest on the South Fork Tolt Reservoir, which is also managed by the City of Seattle as part of the regional water supply.) City ecologists document the nesting success of loons each year.
Two to three pairs of loons return to Chester Morse Lake each year in early March. Although the pairs are present each year, they do not all necessarily establish nests and successfully incubate eggs and raise chicks. Success varies with weather conditions and the ever-present threat of predation.
Males typically arrive in the watershed slightly before females and establish territories. Pairs return to the same territory, and even the same nest site, year after year, where they spend the summer nesting and rearing their chicks.
Loons spend almost all of their time on the water. They walk with difficulty on land, so their nests are usually at the water’s edge. Loons select nest sites on small islands or floating logs in sheltered areas with protection from wind and potential predators.
Females typically lay two eggs each spring. Both females and males take turns on the nest incubating eggs. While one bird remains on the nest, the other rests or forages for food nearby. Both birds are vigilant and always ready to defend the nest against any threat.
Loons incubate the eggs on the nest for 26 to 28 days through all kinds of weather. Loon chicks usually hatch between mid-May and mid-June, depending on when the eggs are laid. Loon parents take their chicks onto the water within a few hours of hatching, feeding and caring for them attentively. Although loon chicks are great swimmers from the first time they touch the water, parents often carry young chicks on their backs for added protection against harsh weather and potential predators.
When lake levels rise in the spring, loon nests can be flooded and destroyed if they are not able to rise with the water. Each year, City ecologists craft artificial nest platforms “landscaped” with soil and vegetation. We hope that loons nest on these floating rafts because they adapt well to changing water levels.
Predators such as river otter or bald eagle can destroy a nest by repeatedly driving adults away or by actually raiding the nest and eating the eggs. Beaver can reach nest sites and crush a clutch of eggs. Loon chicks on the water are also very vulnerable to predation. When they are very young, they cannot yet dive and stay under water to escape.
Many recreational activities such as boating, water skiing, and well-meaning bird watching may disturb loons and keep them from nesting on many lakes. In this area, loons seem to prefer lakes with little to no recreation, and of course, a good food supply.
The City is conducting several studies to better understand the ecology of the common loon in western Washington and the potential effects of reservoir management.
- Common Loon Nesting Ecology: Annual surveys to determine when birds arrive at the reservoirs, the period of nesting and rearing activity, and the outcome of nesting for each pair.
- Common Loon Nest Habitat Assessment: Study to assess the status of loon habitat conditions past and present in the Chester Morse Lake reservoir system and possible effects of future changes and conditions.
- River Delta Plant Community Study: Investigation of the potential impacts of reservoir management on plant communities in the Cedar and Rex deltas (traditional nest territories); and how changes in vegetation communities may affect loon nesting.
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- Cedar River Watershed Habitat Conservation Plan: Common Loon – Measurements of Success
- Washington Department of Fish and Wildlife Status Report for the Common Loon
Other bird species in the watershed: