Eagle Lake

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Lake name:: Eagle Lake
Location:: California
HydroLAKE ID:: 787
Latitude:: 40.652083
Longitude:: -120.727083
Surface area (km2):: 100.7
Basin type:: non-reservoir
Primary emergent vegetation:: Tule (Schoenoplectus spp.)| Tule (Typhus sp. and Sciurpus sp.)| bulrush| bulrush (Scirpus sp.)| hard-stemmed bulrush
Primary vegetation for nesting:: Tule (Schoenoplectus spp.) Tule (Typhus sp. and Sciurpus sp.) bulrush sago pondweed bladderwort bulrush (Scirpus sp.) hard-stemmed bulrush common bladderwort Sago pondweed hard-stemmed bulrush (Schoenoplectus acutus var. occidentalis) Baltic rush (Juncus balticus)
Management agency:: U.S. Forest Service; Bureau of Land Management
Region associations:: Lassen National Forest; Great Basin; Cascades; Sierra Nevada
Comments:: Eagle Lake, in Lassen County, is the second largest lake in California after Clear Lake. It is a natural closed basin lake so water levels vary with inflow. It is situated where the Cascades, Sierra Nevada range, and the Great Basin meet. Recreation has increased in recent years and may cause potential disturbance to waterbirds and other wildlife that use the lake. See footnote from survey data of how important Eagle Lake is to Western and Clark's grebe breeding populations. It is considered the number one breeding lake for grebes in California and a major breeding lake of the intermountain west. There was no nesting from 2012 through 2016. Chicks were observed again in 2017.

Summary of Surveys (25)

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; air
Time period
June 2010, October 2013
Source
Report
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	>1000	5950	2012
Most Recent Adults	>1000	2287	2013
Max Nests	>1000	1496	2011
Most Recent Nests	0	0	2013
Max Chicks	>1000	1200	2011
Most Recent Chicks	0	0	2013

Comments:

1st most important grebe breeding lake in CA. Dry winters (doesn't state years) resulted in very low water levels and grebes couldn't access their traditional nesting habitat. 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. Aerial survey for presence/absence but not widely used for Eagle Lake and Lake Almanor. Steady increase in # adults until 2013 for all lakes except Eagle Lake (likely due to low water levels). Observed active nests also increased through study period except colony collapse at Eagle Lake 2012 and 2013. 2012 and 2013 drought conditions may have negatively impacted to broods.

Survey Citation:
Arsenault, D. 2015. Audubon's Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2014. Final report. Plumas Audubon Society, Plumas and Lassen Counties, California, USA.

Type
shore; boat
Time period
June 2010, September 2014
Source
Report
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	>1000	5950	2012
Most Recent Adults	>1000	2571	2014
Max Nests	>1000	1496	2011
Most Recent Nests	0	0	2014
Max Chicks	>1000	1200	2011
Most Recent Chicks	0	0	2014

Comments:

Natural terminal lake of the Great Basin. See Kyle et al. 2013 for survey methods. 1 population/brood survey per year. Fish kill from anaerobic condition in 2009 could have caused low grebe population in 2010. Nest numbers correlated to water elevation: highest in 2011, then 2010, and lowest in 2012 to 2014. Lack of nesting habitat (inundated tules) in 2012 to 2014 due to such low water levels and there's been no grebe nests those years. Water drawdown is at the slowest rate at this lake compared to the other study lakes. Entered Table 4 only but the adult #s might be counts in September or October (like Lake Almanor) and might have captured migration. Only Lake Almanor has a breakdown of adult count #s per date in the season but none for the other lakes and none in Kyle's report. Water elevation data from Val Aubrey (www.eaglelakefishing.net).

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
N/A
Source
Report
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	1 to 100	presence	2015
Most Recent Adults	1 to 100	presence	2015
Max Nests	0	0	2015
Most Recent Nests	0	0	2015
Max Chicks	0	0	2015
Most Recent Chicks	0	0	2015

Comments:

No adult count #. No nest success. Nest cameras caught storms and high depredation of eggs by gulls. Lowest water levels in the last 140 years. Lack of nesting habitat discouraged nesting. 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 further info on survey timing.

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?	2013
Most Recent Adults	1 to 100	presence?	2013
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 Eagle Lake, no grebe eggs 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:
Elbert, R. A., and D. W. Anderson. 1998. Mercury levels, reproduction, and hematology in Western Grebes from three California lakes, USA. Environ- mental Toxicology and Chemistry 17: 210-213.

Type
shore
Time period
June 1993, September 1994
Source
Peer-reviewed
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	2500	1994
Most Recent Adults	>1000	2500	1994
Max Nests	N/A	N/A	N/A
Most Recent Nests	N/A	N/A	N/A
Max Chicks	>1000	1850	1993
Most Recent Chicks	>1000	1175	1994

Comments:

23 Western and Clark's grebes were collected by shotgun in July and August 1992 from Clear Lake, Eagle Lake, and Tule Lake. Mercury concentrations were analyzed from liver, kidney and breast muscle. No info on how many birds were taken from Eagle Lake and Tule Lake but thirteen birds taken from Clear Lake had higher (double) mercury concentrations in kidney, breast muscle and brain tissue than birds taken from the other lakes. However, mercury concentrations in livers were not statistically different. An abandoned mercury mine within the Clear Lake watershed caused elevated mercury levels in sediment and fish in the lake. Grebe productivity was much lower at Clear Lake than at the other two lakes but not clear why. For the duration of this study, the grebes at Eagle Lake and Tule Lake are thought to be reproducing normally. Eagle Lake has less boat use that is more concentrated at the center of the lake and Tule Lake lacks boating activity. Grebe productivity was also monitored for 3 years from the three lakes. Grebes were surveyed once per month between June to September in 1993 and 1994 at Eagle Lake. About 50 to 75% of the total population of grebe adults and young were counted by spotting scope (ground) and productivity was calculated. Table 2 shows just one summer population count of 2,500 for the 3 years and the productivity rate for each year from 1992 to 1994. No chick #s nor adults #s per year were provided so I solved for # of young given the productivity rate (young to adult ratio) and summer population of 2,500 to come up with chick #s for each year.

Survey Citation:
Feerer, J. L. and R. L. Garrett. 1977. Potential Western Grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 13(1):80-89.

Time period
1976
Source
Journal Article
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	1 to 100	presence?	?
Most Recent Adults	1 to 100	presence?	?
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:

This report presents survey data from spring 1976 of Clear Lake, Eagle Lake, Salton Sea NWR, Topaz Lake, Sacramento NWR, Lake Earl, and Tule Lake (Klamath Basin NWR) and compares to historical data with focus on Clear Lake issues so not much data on Eagle Lake. No info on how surveys were conducted. In 1976, spring population estimate is >1000 (Table 1) but I didn't enter this because it's not during breeding season. 1976 productivity (# hatchlings) is a "?", didn't enter this. Historical breeding reference is Tonwsend 1887. Historical information provided: Gould 1974 estimates breeding Western grebes as 3000 to 4000, however this may be an overestimate from aerial surveys. Eagle Lake is described as large, disjunct, and difficult to survey. Water levels fluctuate much year to year due to changes in seasonal runoff (Gester 1972). However, water levels started to rise due to the ceasing of drawdown for irrigation. This flooding reduced available nesting habitat. No other data provided. From Table 1, colony is not protected, recreation is main use of lake, degree of shoreline development is minimal, spring water level stability is stable, but gradually rising.

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
1887, 1997
Source
Conservation Assessment, Management Plan
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	>1000	1000	1925
Most Recent Adults	501 to 1000	1000	1925
Max Nests	>1000	2487	1996
Most Recent Nests	>1000	1134	1997
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 was presence in 1887 (Grinnell and Miller 1994), they were common in 1905 (Sheldon 1907), 50 adults in 1921, 500 pairs (1000 estimated adults) in Spaulding area in 1925, and 0 nests in 1928 due to "lack of tules" (these last 3 counts by Grinnell et al. 1930). There were 1457 nests in 1970, 1918 nests in 1971 (both sources as Gould 1974), 1200 nests in 1974 (Lederer 1976), 2487 nests in 1996, and 1134 nests in 1997 (both sources as Shaw 1998). Small 1994 considered this a major area.

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
28 August 2002, 10-20 September 2003
Source
Conservation Assessment, Management Plan
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	1427	2003
Most Recent Adults	>1000	1427	2003
Max Nests	>1000	1800	2003
Most Recent Nests	>1000	1800	2003
Max Chicks	501 to 1000	670	2003
Most Recent Chicks	501 to 1000	670	2003

Comments:

2002 field surveys were limited to August 28. The 2003 surveys on Eagle Lake included aircraft, float tube (to sample nests), and brood surveys by boat/canoe. Table 3 population estimate is the # of nests (1800) x 2 for 3600. However, the actual adult count of 1427 was entered here from Table 4. Table 4 counts from D. Anderson, unpub.data. Eagle Lake is considered to be a very important site for grebe nesting with possibly the highest numbers in the world (Gould 1974, Shaw 1998) and largest breeding site of CA. It has an average of "1639 nests from 1970-1997" (Shaw 1998) and "1807 from 1996-2003". This may represent 2.8% of the global population and 22% of the breeding grebes in the Intermountain West (Ivey and Herziger in prep.). Wind and wave threats observed by D. Shaw, pers. comm. and G. Ivey's personal observations. In 2000, nest success was positively correlated to distance from a major boat access and disturbance source and that disturbance negatively impacted clutch size (Sardella 2002). Not sure if this was during breeding season, but avian cholera killed grebes in 1997 at Eagle Lake (National Wildlife Center 1997). A sample of 250 nests monitored on August 23, 2003 showed 118 (52%) hatched, 23 were still being incubated, 15 (6.6%) were most likely depradated, and 94 (41.4%) had no eggs nor eggshell fragments, indicating some kind of failure. There was also evidence of some eggs washed out by waves. Relatively good productivity in 2003 (0.47). Historic productivity up to 2003 ranged from 0.11 to 0.62, averaging 0.43.

Survey Citation:
Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

Time period
N/A
Source
Conservation Plan
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	>1000	3252	1996-2003
Most Recent Adults	>1000	3252	1996-2003
Max Nests	>1000	1626	1996-2003
Most Recent Nests	>1000	1626	1996-2003
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

Appendix D, Table D-2, data is 1626 nests as an average of 1996 to 2003, 3252 area population estimate (nests x 2), population data source is Ivey 2004.

Survey Citation:
Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

Time period
N/A
Source
Conservation Plan
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	101 to 500	362	1996-2003
Most Recent Adults	101 to 500	362	1996-2003
Max Nests	101 to 500	181	1996-2003
Most Recent Nests	101 to 500	181	1996-2003
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

Appendix D, Table D-2, data is 181 nests as an average of 1996 to 2003, 362 area population estimate (nests x 2), population data source is Ivey 2004.

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.

Time period
2017
Source
Report
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	2272	2017
Most Recent Adults	>1000	2272	2017
Max Nests	N/A	?	2017
Most Recent Nests	N/A	?	2017
Max Chicks	>1000	1556	2017
Most Recent Chicks	>1000	1556	2017

Comments:

Breeding at Eagle Lake was observed for the first time since 2011 and was the most productive since the study began. No information on when survey(s) took place nor what methods in 2017. Unknown peak # of nests. No information on species numbers between Western and Clark's grebes. Precipitation from past winter and spring in Northern California increased water levels for tules to grow and provide nesting habitat.

Survey Citation:
Robison, K. M. 2012. A multi-year analysis of brood size and phenology in western and Clark's grebes at two northern California lakes. Thesis. University of California, Davis, California, USA.

Type
boat
Time period
1998, 2010
Source
Thesis
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	1943	2009
Most Recent Adults	>1000	1495	2010
Max Nests	N/A	N/A	N/A
Most Recent Nests	N/A	N/A	N/A
Max Chicks	501 to 1000	548	2008
Most Recent Chicks	1 to 100	49	2010

Comments:

Brood size and phenology comparison study between Western and Clark's on Clear Lake and Eagle Lake. Eagle Lake was considered the control because it is considered remote, uncontaminated and mostly undeveloped. It supports one of the most significant concentrations of nesting grebes in their breeding range (D. Anderson unpub. data, Dolcini 1972, Shaw 1998). Years of exclusion for adult and chick counts (between 1998 and 2010) are 2005 due to lack of data collection and 2007 due to lack of nesting effort. Brood size as a % of n pairs was used to calculate chick count numbers in a given year. However, only half-grown and larger age classes of chicks were included in the data, therefore chick count numbers may be an underestimate. Nest survey was conducted to time the brood survey for peak number of chicks but no actual nest count numbers given. Ratio of Clark's to Western is average over the 11 years surveyed.

Survey Citation:
Sardella, B.A. 2002. The effect of human disturbance on Aechmophorus grebe nest success at Eagle Lake, Lassen County, California. M.Sc. Thesis, California State University, Chico, California.

Type
shore; boat
Time period
15 June 2000, 15 September 2001
Source
Thesis
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	501 to 1000	presumably >500	2000, 2001
Most Recent Adults	501 to 1000	presumably >500	2001
Max Nests	501 to 1000	621	2000
Most Recent Nests	101 to 500	355	2001
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

This was a study quantifying nest success, disturbance and how colony placement was distanced from a historic colony site in proximity to a marina. The most frequent means of human disturbance was through boating. Boats moving through the nesting area or within emergent vegetation zones caused wakes that inundated nests. Though one of the colony sites, Spaulding, is close to an airport and experiences regular airplane fly-overs, the grebes did not seem to be affected by the planes.

Survey Citation:
Robison, R., D. Anderson, and K. Robison. 2018. Landscape-level habitat variables influence reproduction output of Aechmophorus grebes. Waterbirds 41(3): 276-284, 2018.

Type
boat
Time period
14 September 1998, 20 September 2010
Source
Article
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	N/A	N/A	N/A
Most Recent Adults	N/A	N/A	N/A
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:

Grebe reproductive output was sampled annually between 1998 to 2010 except 2005 due to lack of funding. Habitat availability was analyzed and determined to have peaked in 1998 and declined since throughout the study period. The lowest habitat availability was in 2010 when it declined by 93% since 1998. 2010 also demonstrated the lowest habitat quality measurement, having declined by 86% from the highest habitat quality estimate in 2002. No adult nor chick counts in this brief article but productivity is reported as lowest in 2007 (0.087) and 2010 (0.054) representing a 87% and 92% decline respectively from the highest productivity of 0.67 for 2002. The top model showed a positive relationship between grebe reproductive output and habitat availability, which was also the most important value. Not as important but also showing a positive relationship with reproductive output was habitat quality. Lake level was not a direct predictor of grebe reproductive output, but was strongly correlated with habitat availability and quality. Long-term lake level stabilization might even be detrimental to grebe nesting habitat due to its impact on emergent vegetation growth, structure and composition (LaPorte et al. 2014). However, major fluctuations in water levels within a breeding season can negatively effect grebe nesting.

Survey Citation:
Weems, R. E. 2012. Lake elevation and reproductive success in Western and Clark’s grebes at two northern California lakes. M.Sc. Thesis. University of California, Davis, California.

Type
boat; air
Time period
June 1997, October 2010
Source
Thesis
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	N/A	N/A	N/A
Most Recent Adults	N/A	N/A	N/A
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:

Reproductive success and water elevation data were compared for Clear Lake and Eagle Lake. No data collected in 2005. Lake level was determined to be an important factor on population level productivity at a lake but not of individual nest fate. No adult, brood, nor chick numbers provided but I'm assuming the dataset used is the same as Robinson 2012 (her fiance and his thesis from same school, same year) except for the inclusion of years 1997 and 2007. Mean productivity was provided and entered here for the year range of 1997 to 2010. Lake elevation showed a steady decline over the study period.

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
boat
Time period
16 July 2007, 24 August 2007
Source
Report
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	3400	2007
Most Recent Adults	>1000	3400	2007
Max Nests	N/A	N/A	N/A
Most Recent Nests	N/A	N/A	N/A
Max Chicks	101 to 500	145	2007
Most Recent Chicks	101 to 500	145	2007

Comments:

No nest count conducted due to very low chick numbers. Overall adult numbers for 2007 were a fraction of more productive years such as 2002 and 2003. Previously unobserved behavior of multiple adults attending to or feeding one young. There were also several adults with stained plumage that may be indication of exposure to oil spills on the coast. Subsequent reports have their own entries. Anecdotally, water levels were reported as being lower than previous years.

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; boat
Time period
2008
Source
Report
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	2500	2008
Most Recent Adults	>1000	2500	2008
Max Nests	101 to 500	450	2008
Most Recent Nests	101 to 500	450	2008
Max Chicks	>1000	1174	2008
Most Recent Chicks	>1000	1174	2008

Comments:

Data from Table 3. Date of surveys not provided. Productivity rate from # of adults sampled and # of young sampled. Estimated total # of adults is entered here. Water levels the lowest since 1994 (Rathje 2008). According to this report, water would need to be above 5117 feet to flood an ephemeral marsh with good potential to be nesting grebe habitat but those levels haven't been reached since the 1920s. 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
shore; boat; air
Time period
16 June 2009, 16 September 2009
Source
Report
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	4000-5000	2009
Most Recent Adults	>1000	4000-5000	2009
Max Nests	501 to 1000	700	2009
Most Recent Nests	501 to 1000	700	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 rate is somehow calculated at below average productivity. Drought conditions continued into 2009 and limited habitat availability.

Survey Citation:
Bogiatto, R. J., B. A. Sardella, and J. J. Essex. 2003. Food habits of great horned owls in northeastern California with notes on seasonal diet shifts. Western North American Naturalist. 63. 258-263.

Time period
8 August 1989, 8 August 1996
Source
Notes
Both Western and Clarks?
N/A

Count Type	Range	Max	Year
Max Adults	N/A	N/A	N/A
Most Recent Adults	N/A	N/A	N/A
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:

This entry for this particular data from 16 collections of pellets from 2 Great Horned Owl roosts. Hatch-year grebes (both Western and Clark's) were amongst the most common avian prey item in the pellets throughout the year (9.6%). The owls captured them from surface or shoreline.

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Time period
19 August 2003
Source
Database
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	3600	2003
Most Recent Adults	>1000	3600	2003
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:

Check with Gary Ivey on Survey Type "A,M,B". Gary Ivey is observer and source was Ivey (2004). The proportion of Clark's to Western (24:76) is reported in Ivey (2004) too but with different adult survey numbers and different date of survey. Therefore, entering this as another entry and combining Western and Clark's. 3600 is an estimate of adult breeders that is also in the comments of Ivey 2004 for Eagle Lake (but actual count was entered for that entry).

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Time period
1996, 1997
Source
Database
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	>1000	4658	1996
Most Recent Adults	>1000	2064	1997
Max Nests	>1000	2329	1998
Most Recent Nests	>1000	1032	1997
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

Survey type is B. Nest numbers are multiplied by 2 to estimate breeding adults. Daniel Shaw (1998) is the source and observer.

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Time period
1996, 1997
Source
Database
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	501 to 1000	544	1996
Most Recent Adults	101 to 500	204	1997
Max Nests	101 to 500	272	1998
Most Recent Nests	101 to 500	102	1997
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

Survey type is B. Nest numbers are multiplied by 2 to estimate breeding adults. Daniel Shaw (1998) is the source and observer.

Survey Citation:
Plumas Audubon Society. 2016. Audubon’s Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2016 Almanor, Antelope, Davis, and Eagle Lakes, Plumas and Lassen Counties, California.

Type
shore; boat
Time period
2010, 2016
Source
Report
Both Western and Clarks?
Y

Count Type	Range	Max	Year
Max Adults	>1000	3484	2016
Most Recent Adults	>1000	3484	2016
Max Nests	0	0	2015, 2016
Most Recent Nests	0	0	2016
Max Chicks	0	0	2015, 2016
Most Recent Chicks	0	0	2016

Comments:

This entry is for the newest data of 2015 and 2016 because previous years' data is re-reported and already entered. Eagle Lake had not seen nesting since 2011. The lake experienced the lowest water levels in the last 140 years which resulted in a lack of nesting habitat. Yet, of the four lakes in this report, Eagle Lake drops at the lowest rate (-0.15"). This is a very important lake for grebes though, as an estimated 8,000 grebes are found at this lake in the fall. Observer for these two new years was Arsenault. Adult number counts reported in this report is the average of survey totals.

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	>1000	8099*	2015
Most Recent Adults	>1000	8099*	2015
Max Nests	0	0	2015
Most Recent Nests	0	0	2015
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

Water levels lower in 2015 than in last 140 years, lower than in the 1930s when the lake was drained by an earthquake. The >8000 in late August may be mostly migrants so not sure if that should count as the maximum. For the six lakes studied, 2015 was the fourth year of severe drought and nest success was not high.

Survey Citation:
Lederer, R. J. 1976. The breeding populations of piscivorous birds of Eagle Lake. American Birds 30:771-772.

Type
shore; boat
Time period
March 1974, August 1975
Source
Journal Article
Both Western and Clarks?
N

Count Type	Range	Max	Year
Max Adults	>1000	3800	1971
Most Recent Adults	>1000	2400	1974
Max Nests	>1000	presumably >1000	1971, 1972, 1974
Most Recent Nests	>1000	presumably >1000	1971, 1972, 1974
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

The Western grebe population in Eagle Lake may have been the largest in the U.S. and possibly California, according to Gould and Koplin (1971). Lederer compared Gould and Koplin's 1970 and 1971 Western grebe numbers with 1974 survey numbers. Dawson (1974) conducted lake-wide surveys from March through May in 1974, then censuses were conducted three time a month from June through August 1974 and 1975. Table 1 just reports the 1974 numbers and not 1975. Nests were searched for and population numbers were estimated from nest numbers. Other piscivorous birds were surveyed as well and all populations numbers decreased from Gould and Koplin's numbers. Recreation and other human activity have increased over the years at Eagle Lake and high water levels limited nesting habitat. The delay of peak nesting by 3 to 4 weeks may have coincided with a peak in recreation during the summer. Some of these threats are general to grebes and other piscivorous birds. Cannot locate Gould and Koplin (1971) paper that Lederer cites.

Sources of Information

Robison, R., D. Anderson, and K. Robison. 2018. Landscape-level Habitat Variables Influence Reproduction Output of Aechmophorus Grebes. Waterbirds 41(3): 276-284, 2018.; Sardella, B.A. 2002. The effect of human disturbance on Aechmophorus grebe nest success at Eagle Lake, Lassen County, California. M.Sc. Thesis, California State University, Chico, Chico California.; Ivey, G. L. 2004. Conservation Assessment and Management Plan for Breeding Western and Clark’s Grebes in California. 89.; Feerer, J. L., and R. L. Garrett. 1977. Potential western grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 10.; Plumas Audubon Society. 2016. Audubon’s Aechmophorus Grebe Conservation Project Comprehensive Monitoring Report: 2010-2016 Almanor, Antelope, Davis, and Eagle Lakes, Plumas and Lassen Counties, California.; Loggins, D. 2016. Conservation of Aechmophorus Grebe Colonies at Six Northern California Lakes: Final Financial and Programmatic Report for Year One.; 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.
Sardella, B.A. 2002. The effect of human disturbance on Aechmophorus grebe nest success at Eagle Lake, Lassen County, California. M.Sc. Thesis, California State University, Chico, Chico California.
Ivey, G. L. 2004. Conservation Assessment and Management Plan for Breeding Western and Clark’s Grebes in California. 89.
Feerer, J. L., and R. L. Garrett. 1977. Potential western grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 10.
Plumas Audubon Society. 2016. Audubon’s Aechmophorus Grebe Conservation Project Comprehensive Monitoring Report: 2010-2016 Almanor, Antelope, Davis, and Eagle Lakes, Plumas and Lassen Counties, California.
Loggins, D. 2016. Conservation of Aechmophorus Grebe Colonies at Six Northern California Lakes: Final Financial and Programmatic Report for Year One.
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.
Explore Important Bird Areas (IBA) Interactive Map
Eagle Lake Recreation
Eagle Lake Field Station
Geographic Names Information System (GNIS)

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Eagle Lake

Summary of Surveys (25)

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.

Comments:

Survey Citation: Arsenault, D. 2015. Audubon's Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2014. Final report. Plumas Audubon Society, Plumas and Lassen Counties, California, USA.

Comments:

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.

Comments:

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.

Comments:

Survey Citation: Elbert, R. A., and D. W. Anderson. 1998. Mercury levels, reproduction, and hematology in Western Grebes from three California lakes, USA. Environ- mental Toxicology and Chemistry 17: 210-213.

Comments:

Survey Citation: Feerer, J. L. and R. L. Garrett. 1977. Potential Western Grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 13(1):80-89.

Comments:

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.

Comments:

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.

Comments:

Survey Citation: Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

Comments:

Survey Citation: Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

Comments:

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.

Comments:

Survey Citation: Robison, K. M. 2012. A multi-year analysis of brood size and phenology in western and Clark's grebes at two northern California lakes. Thesis. University of California, Davis, California, USA.

Comments:

Survey Citation: Sardella, B.A. 2002. The effect of human disturbance on Aechmophorus grebe nest success at Eagle Lake, Lassen County, California. M.Sc. Thesis, California State University, Chico, California.

Comments:

Survey Citation: Robison, R., D. Anderson, and K. Robison. 2018. Landscape-level habitat variables influence reproduction output of Aechmophorus grebes. Waterbirds 41(3): 276-284, 2018.

Comments:

Survey Citation: Weems, R. E. 2012. Lake elevation and reproductive success in Western and Clark’s grebes at two northern California lakes. M.Sc. Thesis. University of California, Davis, California.

Comments:

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.

Comments:

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.

Comments:

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.

Comments:

Survey Citation: Bogiatto, R. J., B. A. Sardella, and J. J. Essex. 2003. Food habits of great horned owls in northeastern California with notes on seasonal diet shifts. Western North American Naturalist. 63. 258-263.

Comments:

Survey Citation: Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Comments:

Survey Citation: Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Comments:

Survey Citation: Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Comments:

Survey Citation: Plumas Audubon Society. 2016. Audubon’s Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2016 Almanor, Antelope, Davis, and Eagle Lakes, Plumas and Lassen Counties, California.

Comments:

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.

Comments:

Survey Citation: Lederer, R. J. 1976. The breeding populations of piscivorous birds of Eagle Lake. American Birds 30:771-772.

Comments:

Sources of Information

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.

Survey Citation:
Arsenault, D. 2015. Audubon's Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2014. Final report. Plumas Audubon Society, Plumas and Lassen Counties, California, USA.

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.

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.

Survey Citation:
Elbert, R. A., and D. W. Anderson. 1998. Mercury levels, reproduction, and hematology in Western Grebes from three California lakes, USA. Environ- mental Toxicology and Chemistry 17: 210-213.

Survey Citation:
Feerer, J. L. and R. L. Garrett. 1977. Potential Western Grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 13(1):80-89.

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.

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.

Survey Citation:
Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

Survey Citation:
Ivey, G.L., and C.P. Herziger. 2006. Intermountain west waterbird conservation plan, version 1.2. A plan associated with the Waterbird Conservation for the Americas Initiative. Published by U.S. Fish and Wildlife Service Pacific Region, Portland, Oregon.

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.

Survey Citation:
Robison, K. M. 2012. A multi-year analysis of brood size and phenology in western and Clark's grebes at two northern California lakes. Thesis. University of California, Davis, California, USA.

Survey Citation:
Sardella, B.A. 2002. The effect of human disturbance on Aechmophorus grebe nest success at Eagle Lake, Lassen County, California. M.Sc. Thesis, California State University, Chico, California.

Survey Citation:
Robison, R., D. Anderson, and K. Robison. 2018. Landscape-level habitat variables influence reproduction output of Aechmophorus grebes. Waterbirds 41(3): 276-284, 2018.

Survey Citation:
Weems, R. E. 2012. Lake elevation and reproductive success in Western and Clark’s grebes at two northern California lakes. M.Sc. Thesis. University of California, Davis, California.

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.

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.

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.

Survey Citation:
Bogiatto, R. J., B. A. Sardella, and J. J. Essex. 2003. Food habits of great horned owls in northeastern California with notes on seasonal diet shifts. Western North American Naturalist. 63. 258-263.

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Survey Citation:
Ivey, G. 2006. Atlases of waterbird nesting sites for California, Idaho, Oregon and Washington. Region 1 Non Game Program, U.S. Fish and Wildlife Service, Portland, Oregon.

Survey Citation:
Plumas Audubon Society. 2016. Audubon’s Aechmophorus grebe conservation project comprehensive monitoring report: 2010-2016 Almanor, Antelope, Davis, and Eagle Lakes, Plumas and Lassen Counties, California.

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.

Survey Citation:
Lederer, R. J. 1976. The breeding populations of piscivorous birds of Eagle Lake. American Birds 30:771-772.