Thermalito Afterbay
Grebe Survey Summary
- Max Adults: 573
- Year: 2015
- Most Recent Adults: 353
- Year: 2019
- Survey Type: Shore; Boat; Air
- Most Common Threats Reported: Water level too low; water level too high; lack of/poor nesting habitat; wind/wave inundation; egg predation; human/development/boat disturbance; nest abandonment; lack of fish food; water quality/contaminants/oil spills; drought/lack of precipitation/water
- Lake name:
- Thermalito Afterbay
- Location:
- California
- HydroLAKE ID:
- 9215
- GRanD ID:
- 152
- Latitude:
- 39.457142
- Longitude:
- -121.644792
- Surface area (km2):
- 12.5
- Basin type:
- reservoir
- Dam completion date:
- 1967
- Primary emergent vegetation:
- long-leaf pondweed
- Primary vegetation for nesting:
- long-leaf pondweed
- Management agency:
- California Department of Fish and Wildlife; California Department of Water Resources
- Lake use:
- water supply irrigation hydroelectricity
- Region associations:
- Oroville Dam Complex; Lake Oroville; Oroville Wildlife Area; Feather River; Thermalito Forebay
- Comments:
- Part of Oroville Dam Complex, 5th most important grebe breeding lake in CA and they have nested there for at least 20 years. No consistent surveys until Department of Water Resources started in 2004 and now collaborates with Altacal Audubon and Audubon's Grebe Conservation Project. Though number of threats named in this report, human disturbance from waterskiing and water level fluctuation are the main threats behind nest abandonment and low breeding success. Water flows through the Oroville-Thermalito Complex and into the Thermalito Forebay then into Thermalito Afterbay to be used to generate electricity. Altacal Audubon does extensive education and outreach on grebes of the lake.
Surveys (11)
Survey Citation:
Kyle, K., D. Arsenault, N. Lunder, M. Waits, F. Hayes, S. Overlock, J. Patten, and R. Martin. 2013. Conservation of Aechmophorus grebe colonies at six northern California lakes. Final report. Oakland, California, USA.
-
Type
shore; boat -
Time period
June 2010, October 2013 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 501 to 1000 | 520 | 2011 |
| Most Recent Adults | 101 to 500 | 425 | 2013 |
| Max Nests | 101 to 500 | 255 | 2010 |
| Most Recent Nests | 101 to 500 | 210 | 2013 |
| Max Chicks | 101 to 500 | 262 | 2010 |
| Most Recent Chicks | 101 to 500 | 164 | 2013 |
Comments:
Part of Oroville Dam Complex, 5th most important grebe breeding lake in CA and they have nested there for at least 20 years. No consistent surveys until Dept of Water Resources started in 2004 and now collaborates with Altacal Audubon and Audubon's Grebe Conservation Project. Though number of threats named in this report, human disturbance from waterskiing and water level fluctuation are the main threats behind nest abandonment and low breeding success. Nest initiation (started June 1), nest monitoring, and disturbance surveys were weekly. Average of 65 surveys per year on the 6 lakes for adult grebes, nest attempts and young. One to two brood surveys per month starting mid-July to October. For adult count #, "All surveys include the grand total of adults counted on the lake" - not sure what that means. WEGR and CLGR were distinguished if possible but no breakdown in the data reported. Max/min water levels established in 2004 and modified in 2010 to give grebes a more stable water environment.
Survey Citation:
Loggins, D. 2015. Conservation of Aechmophorus grebe colonies at six northern California lakes. Semi-annual financial and programmatic report. Audubon California, Sacramento, California, USA.
-
Type
shore; boat -
Time period
2015 -
Source
Report -
Both Western and Clarks?
N/A
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | presumably >100 | 2015 |
| Most Recent Adults | 101 to 500 | presumably >100 | 2015 |
| Max Nests | 1 to 100 | 75 | 2015 |
| Most Recent Nests | 1 to 100 | 75 | 2015 |
| Max Chicks | 1 to 100 | 7-21 | 2015 |
| Most Recent Chicks | 1 to 100 | 7-21 | 2015 |
Comments:
75 nests and 39 eggs but only 7 nests produced chicks. No data on # of adults nor broods so estimating 7 to 21 chicks (7 successful nests with one to 3 eggs that hatched). Nest cameras caught storms and high depredation of eggs by gulls. "White-faced ibis nested on top of the grebe colony" without harming nor disturbing the grebes. Something similar happened in 2014. Water level stabilized by limiting water drawdown by DWR to 5 feet. Modified Gericke et al. (2006) protocol similar to the last five breeding seasons and included nest initiation surveys (weekly), nest monitoring surveys, disturbance surveys (weekly), and population and brood surveys (1-2 times a month until October). No info on timing of surveys.
Survey Citation:
Ackerman, J. T., C. A. Hartman, C. A. Eagles-Smith, M. P. Herzog, J. Davis, G. Ichikawa, and A. Bonnema. 2015. Estimating mercury exposure of piscivorous birds and sport fish using prey fish monitoring. Environmental Science & Technology 49:13596–13604.
-
Type
boat -
Time period
April 2012, October 2013 -
Source
Peer-reviewed -
Both Western and Clarks?
N/A
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 1 to 100 | presence | 2012 |
| Most Recent Adults | 1 to 100 | presence | 2012 |
| Max Nests | N/A | N/A | N/A |
| Most Recent Nests | N/A | N/A | N/A |
| Max Chicks | N/A | N/A | N/A |
| Most Recent Chicks | N/A | N/A | N/A |
Comments:
Not a survey but grebes were sampled at 25 lakes in CA from April to October of 2012 (13 lakes) and 2013 (12 lakes). An average of 14 grebes per lake (from 2 to 38 grebes) were captured at night with night-lights. No breakdown of actual numbers captured per lake was provided. Morphometry and molt data, along with blood was collected from each bird for mercury analysis, and sex determination via genetic analysis. From 7 out of the 25 lakes, an average of 14 grebe eggs (from 6 to 23 eggs) were collected. An egg from each randomly sampled nest was collected either from an active nest (random egg) or from an abandoned nest (abandoned egg). Prey fish and sport fish were also sampled an average of 11 days after grebe sampling. At Thermalito Afterbay, all tissues were collected in 2012 (Figure SI). 354 grebes were captured total from the 25 lakes, 71% were Western grebes, 29% were Clark's, 48% were female, 52% were male. 101 grebe eggs were collected from 7 lakes, of which 62% were Western grebes, 15% were Clark's grebes, 23% were unidentified which. Grebe blood, eggs, and sport fish mercury concentrations were strongly correlated to mercury concentrations in prey fish at the lakes. Grebe mercury concentrations were also strongly correlated with sport fish mercury concentrations. This study showed that prey fish monitoring can estimate mercury exposure of grebes and other piscivorous birds if these birds can't be sampled directly.
Survey Citation:
Ivey, G. L. 2004. Conservation assessment and management plan for breeding Western and Clark’s Grebes in California. Unpublished technical report. American Trader Trustee Council, California. . Accessed 15 January 2020.
-
Time period
1980s-2000? -
Source
Conservation Assessment, Management Plan -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 1 to 100 | presence | 1980s-2000? |
| Most Recent Adults | 1 to 100 | presence | 1980s-2000? |
| Max Nests | 1 to 100 | presence | 1980s-2000? |
| Most Recent Nests | 1 to 100 | presence | 1980s-2000? |
| Max Chicks | N/A | N/A | N/A |
| Most Recent Chicks | N/A | N/A | N/A |
Comments:
This entry to capture historical record of breeding grebes in CA prior to 2002. There were breeding grebes for at least the past 20 years and noted as colony site, no numbers, years, or other details. Estimated years as 1980s to 2000 due to source year. Sources are J. Snowden and S. Cordes, pers. comm.
Survey Citation:
Ivey, G. L. 2004. Conservation assessment and management plan for breeding Western and Clark’s Grebes in California. Unpublished technical report. American Trader Trustee Council, California. . Accessed 15 January 2020.
-
Type
shore; boat; air -
Time period
5 August 2003, 10-20 September 2003 -
Source
Conservation Assessment, Management Plan -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | 156 | 2003 |
| Most Recent Adults | 101 to 500 | 156 | 2003 |
| Max Nests | 1 to 100 | 95 | 2003 |
| Most Recent Nests | 1 to 100 | 95 | 2003 |
| Max Chicks | 1 to 100 | 100 | 2003 |
| Most Recent Chicks | 1 to 100 | 100 | 2003 |
Comments:
2003 surveys on Thermalito Afterbay included aircraft, shore scoping, and brood surveys by boat/canoe. Table 3 population estimate is the # of nests (95) x 2 for 190. However, the actual adult count of 156 is entered here. Moderate amounts of nesting occurred here in 2003 with 2.6% of the selected sites. Highest productivity in 2003 amongst the selected sites (0.64). This rate may be biased because some non-breeding adults may have left before the brood counts, leaving only 156 adults.
Survey Citation:
Rickard, A. 2017. Conservation of Aechmophorus grebe colonies at six northern California lakes. Interim report for year three submitted to the National Fish and Wildlife Foundation October 31st, 2017. Audubon California, San Francisco, California.
-
Type
boat -
Time period
May 2017, September 2017 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | 233 | 2017 |
| Most Recent Adults | 101 to 500 | 233 | 2017 |
| Max Nests | 1 to 100 | 20 | 2017 |
| Most Recent Nests | 1 to 100 | 20 | 2017 |
| Max Chicks | 1 to 100 | 18 | 2017 |
| Most Recent Chicks | 1 to 100 | 18 | 2017 |
Comments:
2017 productivity was lower than 206 (0.17) and 2015 (0.18). Adult count is an average from late July to September surveys. Grebe count numbers were lower than previous years and attributed to higher water levels that may have impacted grebe behavior and prey fish population.
Survey Citation:
Robison, K., R. Weems, and D. Anderson. 2008. Western and Clark's Grebe conservation and management in California. Annual report for year three (2007). Report for American Trader and Kure/ Stuyvesant Trustee Councils and National Fish and Wildlife Foundation, California.
-
Type
shore; boat -
Time period
20 July 2007, 9 August 2007 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | 330 | 2007 |
| Most Recent Adults | 101 to 500 | 330 | 2007 |
| Max Nests | 1 to 100 | 26 | 2007 |
| Most Recent Nests | 1 to 100 | 26 | 2007 |
| Max Chicks | 0 | 0 | 2007 |
| Most Recent Chicks | 0 | 0 | 2007 |
Comments:
Subsequent reports have their own entries. Maximum and most recent nest numbers were totaled from two colonies. No chicks were observed so nests were assumed to have all failed due to the threats listed.
Survey Citation:
Robison, K., R. Weems, and D. Anderson. 2008. Western and Clark's Grebe conservation and management in California. Annual report for year four (2008). Report for American Trader and Kure/ Stuyvesant Trustee Councils and National Fish and Wildlife Foundation, California.
-
Type
shore; air -
Time period
2008 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | 300 | 2008 |
| Most Recent Adults | 101 to 500 | 300 | 2008 |
| Max Nests | 1 to 100 | 99 | 2008 |
| Most Recent Nests | 1 to 100 | 99 | 2008 |
| Max Chicks | 1 to 100 | 35 | 2008 |
| Most Recent Chicks | 1 to 100 | 35 | 2008 |
Comments:
Data from Table 3 collected by R. Martin of CA Department of Water Resources. Date of surveys not provided. Productivity rate from # of adults in sample and # of young in sample. Estimated total # of adults is entered here. Water ski course ran through a grebe colony. No other information provided. Subsequent reports have their own entries.
Survey Citation:
Robison, K., R. Weems, D. Anderson, and F. Gress. 2010. Western and Clark's Grebe conservation and management in California. Annual report (2009). Report for California Institute of Environmental Studies, Davis, California.
-
Type
boat -
Time period
October 2, 2009 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 101 to 500 | 364 | 2009 |
| Most Recent Adults | 101 to 500 | 364 | 2009 |
| Max Nests | 101 to 500 | 315 | 2009 |
| Most Recent Nests | 101 to 500 | 315 | 2009 |
| Max Chicks | N/A | N/A | N/A |
| Most Recent Chicks | N/A | N/A | N/A |
Comments:
Data from Table 1. There is no chick # but productivity is 0.52. Data source is Ryan Martin (CADWR).
Survey Citation:
Loggins, D. 2016. Conservation of Aechmophorus grebe colonies at six northern California lakes: final financial and programmatic report for year one. Audubon California, Sacramento, California, USA.
-
Time period
2015 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 501 to 1000 | 573 | 2015 |
| Most Recent Adults | 501 to 1000 | 573 | 2015 |
| Max Nests | 101 to 500 | 140 | 2015 |
| Most Recent Nests | 101 to 500 | 140 | 2015 |
| Max Chicks | 101 to 500 | 164 | 2015 |
| Most Recent Chicks | 101 to 500 | 164 | 2015 |
Comments:
Thermalito Afterbay is surveyed by Altacal Audubon. For the six lakes studied, 2015 was the fourth year of severe drought and nest success was not high.
Survey Citation:
Altacal Audubon Society. 2020. Conservation of Aechmophorus grebe colonies at Thermalito Afterbay, Oroville, California, 2010 to 2020 surveys & monitoring final report. Chico, California.
-
Type
shore; boat -
Time period
29 May 2010, 4 September 2019 -
Source
Report -
Both Western and Clarks?
Y
| Count Type | Range | Max | Year |
|---|---|---|---|
| Max Adults | 501 to 1000 | 580 | 2015 |
| Most Recent Adults | 101 to 500 | 353 | 2019 |
| Max Nests | 101 to 500 | >261 | 2010 |
| Most Recent Nests | 1 to 100 | >63 | 2019 |
| Max Chicks | 101 to 500 | 341 | 2014 |
| Most Recent Chicks | 1 to 100 | 82 | 2019 |
Comments:
Final report from 2010 to 2019 for Thermalito Afterbay, the fifth most important breeding lake in California. This lake has relatively stable water but California Department of Water Rresources can still raise or lower water by 1.5 to 2 feet within a short time span which can cause nest abandonment. This lake is also vulnerable to high winds. There is a results table for adult and chick count number but nest numbers were culled from the annual narratives. Nests and nest attempts were interpreted to be the same. Adult and chick counts might vary in method of determining averages per year. 2014 had the highest productivity while 2018 had the lowest productivity. There was a five foot drop in water elevation due to power plant repairs that impacted nests but water was relatively stable thereafter. Disturbance surveys were conducted as well as adult, nest, and brood surveys. Water skiiers and ski boats was the most frequent disturbance.
Sources of Information
- Kyle, K., D. Arsenault, N. Lunder, M. Waits, F. Hayes, S. Overlock, J. Patten, and R. Martin. 2013. Conservation of Aechmophorus Grebe Colonies at Six Northern California Lakes. Final Report.; Messager, M. L., B. Lehner, G. Grill, I. Nedeva, and O. Schmitt. 2016. Estimating the volume and age of water stored in global lakes using a geo-statistical approach. Nature Communications 7:13603. Data is available at www.hydrosheds.org.; Lehner, B., C. Reidy Liermann, C. Revenga, C. Vorosmarty, B. Fekete, P. Crouzet, P. Doll, M. Endejan, K. Frenken, J. Magome, C. Nilsson, J.C. Robertson, R. Rodel, N. Sindorf, and D. Wisser. 2011. Global Reservoir and Dam Database, Version 1 (GRanDv1): Dams, Revision 01. Palisades, New York: NASA Socioeconomic Data and Applications Center (SEDAC).
- Messager, M. L., B. Lehner, G. Grill, I. Nedeva, and O. Schmitt. 2016. Estimating the volume and age of water stored in global lakes using a geo-statistical approach. Nature Communications 7:13603. Data is available at www.hydrosheds.org.
- Lehner, B., C. Reidy Liermann, C. Revenga, C. Vorosmarty, B. Fekete, P. Crouzet, P. Doll, M. Endejan, K. Frenken, J. Magome, C. Nilsson, J.C. Robertson, R. Rodel, N. Sindorf, and D. Wisser. 2011. Global Reservoir and Dam Database, Version 1 (GRanDv1): Dams, Revision 01. Palisades, New York: NASA Socioeconomic Data and Applications Center (SEDAC).
- Oroville-Thermalito Complex
- Grebes at Thermalito Afterbay
- Thermalito Forebay Recreation
- Oroville Wildlife Area
- Harmful Algal Bloom (HAB) Advisories
- Geographic Names Information System (GNIS) for Lake Earl