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Approximately 2,000 grebes of the Clark and western species are currently nesting in the shallow waters of Lake Almanor. Photo by David Hamilton, Plumas Audubon Society
Have you ever wondered at all the mounds of vegetation that have been piled up in the shallow shore waters of Lake Almanor? They are actually floating nests that have been constructed by western and Clark’s grebes.
They can be seen just south of the Chester Causeway where the grebe nest colony has spread out all the way to the mouth of the Feather River.
There are also nesting colonies along Highway 89 from Lake Almanor West to near the mouth of the Chester Flood Control Channel (aka super ditch).
The Plumas Audubon Society has been monitoring grebes in Plumas and Lassen counties since 2010, and this year we have documented more nests on the Lake Almanor than have been recorded in any previous studies.
In fact, Lake Almanor has one of the largest breeding populations of western and Clark’s grebes in California.
How to help nesting grebes and their newly hatched chicks
If the grebes feel threatened they will temporarily leave their nest and the vacant nests will then attract gulls and ravens that will quickly consume eggs.
How can you help? Stay 300 feet away from the grebe nest colonies while observing the birds, and refrain from kayaking or canoeing through active nest colonies.
Entanglement kills many grebes each year.
How can you help? Properly dispose of used fishing line and garbage.
Grebes leave their nests immediately after all of the eggs have hatched, and carry their young on their back for their first few weeks of life. This is called back-brooding. Forcing back-brooding parents to dive can result in drowned young birds.
How can you help? Avoid driving through large groups of grebes between now and late September as many grebes are back-brooding.
During the monitoring, Lake Almanor had approximately 550 grebe nests in 2010 and 2011 and then 900 in 2012. As of mid-August, there are around 2,000 grebe nests on Lake Almanor and the grebes are still actively nesting.
Grebes are highly specialized diving birds; they cannot walk on land. They build these floating nest mounds using lake vegetation in areas where the water depth allows them to swim to and from their nests.
When the lake water drops during the nesting season to an unsafe level the grebes abandon those nests, unfortunately leaving the eggs that remain to be consumed by predators. The grebes then find another place to construct a new nest mound.
We have found that the grebe nesting colonies are dynamic in that they nest in different locations each year and change nesting locations throughout the season. They do so depending on the lake’s water level, which affects their available nesting habitat.
Because Pacific Gas and Electric Co. manages Lake Almanor for power production and downstream water use, water levels fluctuate throughout the year, especially in late summer when the grebes are nesting.
These changes in water level can negatively impact grebe-nesting success so Plumas Audubon spends a lot of time watching the grebes.
We perform surveys to see which animals are consuming the adults (river otters, bald eagles), their eggs (gulls, ravens) and their young (fish, gulls, ravens).
We also do surveys to see what types of disturbances there are in the nest colonies: kayakers, airplanes, helicopters, fishermen and off-highway vehicles.
In estimating nest numbers we hike the shoreline, wade through mud, kayak and conduct boat surveys. The boat surveys provide us with important data on the lake’s total grebe population.
During these surveys we count the total number of grebes residing on the lake as well as the number of offspring; these data tell us how successful their nesting attempts have been.
To learn more about the grebes and the work the Plumas Audubon Society does in Northeastern California, or to become a member, visit plumasaudubon.org.
For answers to specific questions about the grebe study call Nils Lunder, outreach and education coordinator, at 530-258-6936.
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