Aechmophorus Grebe Monitoring Results
In our fifteenth year of monitoring Aechmophorus grebes at Northern California lakes, Plumas Audubon Society has been working to analyze how lake users, reservoir managers, and downstream water users influence grebe breeding success. We hope that our work will lead to increases in suitable nesting habitat for the grebes in ways that do not negatively impact lake users. All of the lakes currently in our study area are man-made reservoirs, thus a focus during these surveys is observing the effect that reservoir level management has on available nesting habitat, reproductive success rates, and predation on both adult grebes as well as their eggs.
Nesting Habitat
Lake Almanor Results 2010-2024
Once again, the nesting colonies of grebes at Lake Almanor were abandoned due dramatic changes in reservoir elevation, leaving nests stranded along the shore. In 2024, a total of 5,933 nesting attempts were recorded by PAS staff at Lake Almanor. Of these nesting attempts, only 104 juvenile grebes were observed. That is a nesting success rate of 0.0058 %. To recount, that is:
Western and Clark’s grebes had a tremendous struggle setting up their colony during the 2024 breeding season. In June, PAS observed the birds initially settled into the emergent cattails and willows on the margins of Lake Almanor. As reservoir elevation began rapidly dropping, most grebes dispersed south, and the active nesting colony shifted closer to open water. Some grebes opted to move north, but this dispersal also failed to offer a brighter outcome. Between July 8 and September 8, reservoir elevation at Lake Almanor dropped -5.07 feet. Nests that were previously being incubated were abandoned, leaving behind 5,933 nests, many with two to three unhatched eggs.
The peak juvenile-to-adult ratio in 2024 was 0.027 %. While this rate falls short of our objective definition of success—the goal being to achieve a reproductive success rate above 0.35 % juveniles to adults—it is the highest of the seven most recent study years.
During the breeding season each year from 2019 to 2024, rapid reservoir elevation drop rates contributed to complete abandonment of large breeding colonies and the resulting low productivity in those years, creating long-term impacts for the grebe populations. Cumulatively speaking, all of the past six populations of Aechmophorus grebes have been impacted by decreasing breeding habitat availability, resulting a total loss of over 81% of all documented nest attempts. PG&E has worked with Audubon since 2018 to improve conditions for grebes and avoid unnecessary take of Aechmophorus grebe eggs during their breeding season at Lake Almanor. Unfortunately, these objectives have yet to be attained.
PAS continues to be actively engaged in advocating for sustainable water policy with Pacific Gas & Electric Co. (PG&E), specifically influencing water release decisions. PAS is working to ensure that PG&E incorporates measures for the protection of Aechmophorus grebes into their plan for reservoir operations, particularly related to the consideration of their nesting habitat. This aligns with our broader commitment to advancing policy that supports conservation and climate initiatives, safeguarding bird habitats, and addressing the pressing issue of climate change.
Please sign our Change.org petition urging Pacific Gas & Electric Co. to manage water levels at Lake Almanor with drop rates of no more than 0.72 inches per day during critical grebe breeding season (June 25th through September 15th):
Click here to sign, it only takes a few minutes to make a big difference: http://chng.it/qJwmBksmGg
- 788 abandoned nests in 2016
- 1,205 abandoned nests in 2018
- 657 abandoned nests in 2019
- 470 abandoned nests in 2020
- 1,468 abandoned nests in 2022
- 864 abandoned nests in 2023
- 5,933 abandoned nests in 2024
Western and Clark’s grebes had a tremendous struggle setting up their colony during the 2024 breeding season. In June, PAS observed the birds initially settled into the emergent cattails and willows on the margins of Lake Almanor. As reservoir elevation began rapidly dropping, most grebes dispersed south, and the active nesting colony shifted closer to open water. Some grebes opted to move north, but this dispersal also failed to offer a brighter outcome. Between July 8 and September 8, reservoir elevation at Lake Almanor dropped -5.07 feet. Nests that were previously being incubated were abandoned, leaving behind 5,933 nests, many with two to three unhatched eggs.
The peak juvenile-to-adult ratio in 2024 was 0.027 %. While this rate falls short of our objective definition of success—the goal being to achieve a reproductive success rate above 0.35 % juveniles to adults—it is the highest of the seven most recent study years.
During the breeding season each year from 2019 to 2024, rapid reservoir elevation drop rates contributed to complete abandonment of large breeding colonies and the resulting low productivity in those years, creating long-term impacts for the grebe populations. Cumulatively speaking, all of the past six populations of Aechmophorus grebes have been impacted by decreasing breeding habitat availability, resulting a total loss of over 81% of all documented nest attempts. PG&E has worked with Audubon since 2018 to improve conditions for grebes and avoid unnecessary take of Aechmophorus grebe eggs during their breeding season at Lake Almanor. Unfortunately, these objectives have yet to be attained.
PAS continues to be actively engaged in advocating for sustainable water policy with Pacific Gas & Electric Co. (PG&E), specifically influencing water release decisions. PAS is working to ensure that PG&E incorporates measures for the protection of Aechmophorus grebes into their plan for reservoir operations, particularly related to the consideration of their nesting habitat. This aligns with our broader commitment to advancing policy that supports conservation and climate initiatives, safeguarding bird habitats, and addressing the pressing issue of climate change.
Please sign our Change.org petition urging Pacific Gas & Electric Co. to manage water levels at Lake Almanor with drop rates of no more than 0.72 inches per day during critical grebe breeding season (June 25th through September 15th):
Click here to sign, it only takes a few minutes to make a big difference: http://chng.it/qJwmBksmGg
Plumas Audubon Society Annual Reports
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Press Release: 2020 & 2019 Monitoring Summary
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Comprehensive Monitoring Report
Clear Lake Grebe Reports
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