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Clear Lake

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Lake name:
Clear Lake
Location:
California
HydroLAKE ID:
794
Latitude:
39.075520
Longitude:
-122.861607
Surface area (km2):
176.7
Basin type:
non-reservoir
Primary emergent vegetation:
Tule (Typhus sp. and Sciurpus sp.)| tules (Schoenoplectus spp.)| hardstem bulrush
Primary vegetation for nesting:
bulrush (Scirpus sp.) Tule (Typhus sp. and Sciurpus sp.) Along shore: tules (Schoenoplectus spp.) smartweed (Persicaria spp.) water primrose (Ludwigia peploides) willows (Salix spp.). In open water: pondweed (Stuckenia spp.) bulrush various pondweeds and submerged aquatic plants
Management agency:
California Department of Parks and Recreation; U.S. Forest Service; Bureau of Land Management
Region associations:
Clear Lake State Park
Comments:
Clear Lake, in Lake County of northern California, is the oldest lake in North America and one of the largest freshwater lakes of the state. Clear Lake has been particularly impacted by adverse anthropogenic activity such as acid mine drainage and mining activities that leached mercury into the lake, the use of dichlorodiphenyldichloroethane (DDD) to control Clear Lake gnat populations, introduced nonnative fishes, and the destruction of wetland habitats to development. It is highly productive and shallow. Considered the third most important grebe breeding lake in the state, it is impacted by various threats and grebes have had consistently low productivity. See survey data footnotes for more information.

Summary of Surveys (27)

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
    July 2011, October 2013
  • Source
    Report
  • Both Western and Clarks?
    N
Count Type Range Max Year
Max Adults >1000 8250 2013
Most Recent Adults >1000 8250 2013
Max Nests >1000 2737 2013
Most Recent Nests >1000 2737 2013
Max Chicks 101 to 500 361 2012
Most Recent Chicks 101 to 500 211 2013

Comments:

3rd most important grebe breeding lake in CA (Ivey 2004). Recent threats to breeding success are natural events, water quality, low water level from drought, and die-off of prey like threadfin shad and silversides in 2011. Colony collapse in 2011. Increased levels of predation (crows and gulls) and nests destroyed by wind. Possible threats also nutrient loading and heavy metals. Human disturbance from fishing and boating was a greater threat in the past than recently. 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 brood survey in Sept for Clear Lake. Number of adults at Clear Lake in 2010 and 2011 is from September survey, and in 2012 and 2013 is from July survey. WEGR and CLGR were distinguished if possible but no breakdown in the data reported. Despite 2012 and 2013 drought conditions, grebes at Clear Lake produced more young compared to 2010 and 2011 wet years. This hints at other factors that may be at play that impact breeding success. "Consistently low rate of reproduction at Clear Lake."

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.

  • Time period
    N/A
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 presumably >1000 2014, 2015
Most Recent Adults >1000 presumably >1000 2015
Max Nests >1000 <6000 2014
Most Recent Nests 501 to 1000 888 2015
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

No nest success. Nest cameras caught storms and high depredation of eggs by gulls. Reproductive effort and nest success the lowest observed since 2010. Major wildfires in 2015 but didn't effect breeding grebes on the lake. Wind and avian predators were the biggest threats to grebe breeding success. Insufficient food also presumed to icause high rate of abandonment. In 2015, 21 colonies, 96% of them open water nests vulnerable to predation and disturbance (human and avian) but many abandoned without disturbance being documented. Strong winds in 2015 blew ashore over a hundred nests. 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).

Survey Citation:
Suchanek, T.H., P.J. Richerson, D.C. Nelson, C.A. Eagles-Smith, D.W. Anderson, J.J. Cech, Jr., G. Schladow, R. Zierenberg, J.F. Mount, S.C. McHatton, D.G. Slotton, L.B. Webber, A.L. Bern and B.J. Swisher. 2002. Evaluating and managing a multiply-stressed ecosystem at Clear Lake, California: A holistic ecosystem approach. Managing For Healthy Ecosystems: Case Studies, CRC/Lewis Press. pp. 1233-1265 (in press).

  • Type
    boat; air
  • Time period
    1992, 2001
  • Source
    Peer-reviewed
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 presumably >1000 1996 - 2001
Most Recent Adults >1000 presumably >1000 2001
Max Nests >1000 mean 1250 1996 - 2001
Most Recent Nests >1000 mean 1250 1996 - 2001
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

Comparison study with osprey. Nesting grebes monitored from 1992 to 2001. Feather sampling for Hg. Feathers collected for Hg sampling in 1992, 1998 and after 2001 (2003 and 2006). Historical feather samples taken from museum specimens from 1967 to 1969 by Hermann et al., which measured ~2.3 times greater Hg levels than feathers from 1992. Fluctuation in Hg levels during 10 year study period. Total nest failure in 1999 probably due to water drawdown that stranded nests. Low productivity and nest failures in 1993-1995 and 1997 and 1999 were attributed to various disturbances. Type of disturbances unspecified for 1993-1995 and 1997. 1999 was zero nests due to low water levels. Human disturbance seems to be the most major threat. No major population effects of the Hg on grebes during the study though there is some evidence of Hg toxicity prior to mine remediation. No population data provided, only graph of productivity but no numbers. Study divided into early (1992–1995) for pre-remediation and late (1996–2001) for post-remediation. Interpreted box plots (figure 4) to estimate approximate # nests as numbers were not provided. Method of surveys were open water (I'm assuming boat) and low-level aerial photography (assuming plane) for species composition, brood sizes, age, and adult to young ratio. Nesting grebe numbers estimated by counting parts of each colony and projecting densities to the whole colony along with assessing through aerial photos. Colony progress was monitored through the breeding season and compared to Eagle Lake. In 1992, Hg residues in grebes of Clear Lake were higher compared to Eagle Lake and Tule Lake, and near threshold levels that effect reproduction in birds.

Survey Citation:
Cahill, T. M., D. W. Anderson, R. A. Elbert, B. P. Perley, and D. R. Johnson. 1998. Elemental Profiles in Feather Samples from a Mercury-Contaminated Lake in Central California. Archives of Environmental Contamination and Toxicology 35:75–81.

  • Time period
    N/A
  • Source
    Peer-reviewed
  • 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:

Feathers collected from 12 adult Western grebes to test for mercury concentrations compared to osprey. Mercury concentrations varied between the species but "sulfur concentrations were comparable". Birds at Clear Lake ecosystem exhibited higher mercury concentrations compared to other sites. Osprey was main species of study.

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 Clear Lake, 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:
Elbert, R. A., and D. W. Anderson. 1998. Mercury levels, reproduction, and hematology in western grebes from three California Lakes, USA. 4.

  • Type
    boat
  • Time period
    June 1992, September 1994
  • Source
    Peer-reviewed
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 3500 1994
Most Recent Adults >1000 3500 1994
Max Nests N/A N/A N/A
Most Recent Nests N/A N/A N/A
Max Chicks 501 to 1000 560 1993
Most Recent Chicks 101 to 500 210 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. The thirteen birds 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. Disturbance and bioaccumulation of compounds including mercury could impact productivity. There are many boaters, skiers, and anglers at that lake. In comparison, 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 in 1992, then once per month between June to September in 1993 and 1994. About 50 to 75% of the total population of grebe adults and young were counted by boat and productivity was calculated. Table 2 shows just one summer population count of 3,500 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 3,500 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. 10.

  • Time period
    1967, 1976
  • Source
    Journal Article
  • Both Western and Clarks?
    N
Count Type Range Max Year
Max Adults 101 to 500 400 1973
Most Recent Adults 101 to 500 200 1975
Max Nests 101 to 500 165 1967
Most Recent Nests 0 0 1976
Max Chicks 0 0 1976
Most Recent Chicks 0 0 1976

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. Different years report different kinds of survey data either in Table 1, Table 2, or in narrative and I combined historical data with this survey in this entry. In 1967 # of nests was 165 and no adult #s given, in 1973 # of nests was 49 and 200 pairs (400 estimated breeding adults), in 1975 # of nests was 36 and 100 pairs (200 estimated breeding adults), in 1976 was no nests nor hatchlings (chronic low water levels) and 200 spring adult population estimate (outside breeding season). No info on how surveys were conducted. In 1975, colony observed in April, May, June, July but no other details on timing of other years. Historical information provided: in 1910, "large #s" of Western grebes were nesting there (Finley 1911), in the 1940's, >1,000 pairs (2,000 estimated breeding adults) according to A.H. Miller (Hunt and Bischoff 1960), but then in 1967, the colony was limited to one tule marsh. Clutch size dropped 13% from 1967 to 1975 from 2.42 to 2.10 eggs. In 1975, clutches were no greater than 3 eggs. In 1975, 7 eggs were collected to measure eggshell thickness and they were significantly thin-shelled (except for one egg). This article names the major threats to grebes on this lake over time as these 3: various periods of pesticide use starting on 1949 to rid Clear Lake gnats and subsequent reproductive failure and disappearance of breeding grebes, the introduction of Mississippi silversides to control gnats and their competition with the grebes' prey fish (young centrachids) from which the grebes never switched from as prey, and the destruction of emergent vegetation that was traditional nesting habitat due to commercial development of the shoreline. From Table 1, colony is not protected, recreation is main usage, degree of shoreline development is high, and spring water level stability considered usually stable with high winds.

Survey Citation:
Hayes, F. E., D. G. Turner, N. D. Zimmerly, and M. B. Peralta. 2018. Nocturnal courtship, copulation, and egg-laying in the western grebe (Aechmophorus occidentalis) and Clark’s grebe (Aechmophorus clarkii). Journal of Ethology 36:65–75.

  • Time period
    15 June 2014, 4 September 2016
  • Source
    Journal Article
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 presumably >1000 2014-2016
Most Recent Adults >1000 presumably >1000 2016
Max Nests >1000 5936 2014
Most Recent Nests >1000 4993 2016
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

Article on nocturnal copulation of Western and Clark's where they set cameras within the colonies between 2014 to 2016 and report the number nests per year (entered here). Reports that nocturnal copulation may be to avoid disturbances and predation and other threats, noted in this entry.

Survey Citation:
Hayes, F. E., D. G. Turner, B. J. McIntosh, D. E. Weidemann, N. D. Zimmerly, M. B. Peralta, D. B. Stoppelmoor, and M. E. Hellie. 2018. Floating bird nests provide resources for wildlife: ecological roles of vertebrates using Aechmophorus grebe nests at Clear Lake, California. Wetlands Ecology and Management 26:1061–1072.

  • Time period
    N/A
  • Source
    Journal 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:

Article was about invertebrates and vertebrates that use floating grebe nests and the functions that grebe nests serve in an environment. This entry included to capture information on emergent and submergent vegetation used as grebe nest material at Clear Lake whether along shore or in the open water.

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.

  • Time period
    N/A
  • Source
    Conservation Assessment, Management Plan
  • Both Western and Clarks?
    N/A
Count Type Range Max Year
Max Adults >1000 presumably >1000 1911, 1940s, 1958-1961
Most Recent Adults 1 to 100 presence 1911, 1940s, 1958-1961
Max Nests >1000 >1000 1940s
Most Recent Nests 1 to 100 16 1961
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

This entry to capture historical records of breeding grebes in CA prior to 2002. There were >1000 nests in the 1940s (Grinnell and Miller 1944), 0 nests in 1958 to 1960 (Herman et al. 1969), and 16 nests in 1961 (Herman et al. 1969). Small 1994 considered it a "major nesting area". Likewise, Finley 1911 and Small 1994 considered it a "major area" for breeding grebes in 1911 after the dam was built.

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.

  • Type
    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 501 to 1000 995 2003
Most Recent Adults 501 to 1000 995 2003
Max Nests 101 to 500 470 2003
Most Recent Nests 101 to 500 470 2003
Max Chicks 101 to 500 191 2003
Most Recent Chicks 101 to 500 191 2003

Comments:

Table 3 population estimate is the # of nests (470) x 2 for 940. However, the actual adult count of 995 was entered here from Table 4. Table 4 counts from D. Anderson, unpub.data. This lake is the 3rd most important of the selected sites with 12.8%. It has not bounced back from pre-DDD nest numbers of over 1,000. Low water levels and human disturbance resulting in nest abandonment and predation, along with cattle intrusion into the colony, was noted by D. Anderson, pers. comm. D. Anderson has attributed boating recreation towards colony failures as reproduction has happened in 3 years out of 12-years of grebe monitoring. Also, in 1997 and 2002, most grebe nests were destroyed possibly due to airboat use for weed control operations (D. Anderson, pers. comm.). DDD contaminants may have resulted in high adult mortality (Herman et al. 1969) but there may have been stress from mercury and other additional contaminants as well (Suchanek et al. 2002). DDD presence has degraded but low levels of contamination might persist, causing egg shell thining and population recovered to about half of its levels prior to DDD (D. Anderson, pers. comm.) as of time of this report. On August 20, G. Ivey returned to the Tule Point colony of ~350 nests observed on August 5, and found no evidence of them remaining. They may have been abandoned for unknown reasons and destroyed by wind/waves.

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. 7.

  • Type
    shore; boat
  • Time period
    30 April 2017, 15 September 2017
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 4560 2017
Most Recent Adults >1000 4560 2017
Max Nests >1000 5075 2017
Most Recent Nests >1000 5075 2017
Max Chicks 501 to 1000 599 2017
Most Recent Chicks 501 to 1000 599 2017

Comments:

This report extrapolates the number of juveniles to adults in the survey area to the adult count as an estimate of 1151 juveniles. I entered the actual juvenile count (599) and didn't enter this extrapolation. Nesting in 2017 started earlier than the previous seven years of breeding. First chick was sighted on May 6, estimating that egg laying occured before April 13. Cameras were deployed to capture predation and disturbance activity. Number of nests were 2nd highest since the study began in 2010. Results for 2017 suggests correlation of nesting success with high water levels when wind/wave and boat disturbance doesn't occur.

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 2524 2005
Most Recent Adults >1000 2377 2010
Max Nests N/A N/A N/A
Most Recent Nests N/A N/A N/A
Max Chicks 101 to 500 217 2000
Most Recent Chicks 1 to 100 78 2010

Comments:

Brood size and phenology comparison study between Western and Clark's on Clear Lake and Eagle Lake. Years of exclusion for adult and chick counts between 1998 and 2010 are 1999 and 2002 due to human disturbance affecting nesting effort, and 2007 and 2008 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 9 years surveyed.

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. 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 at nesting areas were highly variable within the study period.

Survey Citation:
Shuford, W.D., D.L. Thomson, D.M. Mauser, and J. Beckstrand. 2004. Abundance, distribution, and phenology of nongame waterbirds in the Klamath Basin of Oregon and California. PRBO Conservation Science. Final report to U.S. Fish and Wildlife Service, Klamath Basin National Wildlife Refuge Complex, Tulelake, California, USA.

  • Type
    air
  • Time period
    12 June 2003, 23 June 2003
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults 1 to 100 64 2003
Most Recent Adults 1 to 100 64 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:

Surveyed for 3 periods: spring migration, mid-breeding, and fall migration in 2003. Numbers here are just during mid-breeding season (June 12 to 23). Adult count is lumped between the two species.

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 June 2007, 14 September 2007
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 8000 2007
Most Recent Adults >1000 8000 2007
Max Nests 1 to 100 8 2007
Most Recent Nests 1 to 100 8 2007
Max Chicks 1 to 100 20 2007
Most Recent Chicks 1 to 100 20 2007

Comments:

There was a large thread-fin shad die off earlier in 2007, a prey fish of the grebes. There were very few nests and no large colony established. Multiple threats attributed to this lake-wide failure in nesting in 2007. About 5 birds had stained plumage (possible evidence of oil exposure) which was the most observed since 1992. Airboat had plowed through emergent vegetation, possibly for Hydrilla control. Subsequent reports have their own entries.

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.; 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.; 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
    2000, 2009
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 7646 2007
Most Recent Adults >1000 2149 2009
Max Nests >1000 2675 2000
Most Recent Nests 101 to 500 500 2009
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

From Table 2 of 2007 report, Table 1 of 2008 report, and Table 2 of 2009 report. No details on date of surveys per year in these tables. These numbers are different from those reported in other years and adult count numbers are "sample-size for productivity" so may not represent total numbers. Adult numbers may include some surveys done after nesting. The main takeaway is that nesting effort in 2007 and 2008 is much lower than in previous years. There was no large nest colony in 2007 and the colony initiation failed in 2008. Drought conditions continued into 2009, limiting nesting habitat. However, a nesting colony was initiated in 2009, the first one since 2006, an surveyed by air and boat in mid-August. In early October, a brood survey found no evidence of the colony remaining. There were very few broods observed on that survey and the apparent nesting failure may have been due to wind or some other cause. Also there were very low numbers of chicks in 2002. Productivity is average across the 10 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; air
  • Time period
    27 June 2008, 20 September 2008
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 4500 2008
Most Recent Adults >1000 4500 2008
Max Nests 1 to 100 <=25 2008
Most Recent Nests 1 to 100 <=25 2008
Max Chicks 1 to 100 8 2008
Most Recent Chicks 1 to 100 8 2008

Comments:

Data from Table 3. Productivity rate from # of adults in sample and # of young in sample. Estimated total # of adults is entered here. nesting effort in 2007 and 2008 is much lower than in previous years, there was no large nest colony in 2007 and the colony initiation failed in 2008. A historical and less-disturbed nesting area did not have enough water to inundate it. 2008 considered a second year of nesting failure. 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
    shore; boat; air
  • Time period
    11 July 2009, 4 October 2009
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 7500 2009
Most Recent Adults >1000 3000 2009
Max Nests 101 to 500 450-500 2009
Most Recent Nests 101 to 500 400-450 2009
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

Data from Table 1. No chick count #s but productivity is calculated as 0.022.

Survey Citation:
Schlorff, R. 1983. Nongame wildlife investigations. Job progress report for inland nesting waterbird survey, Job number III-2, project number W-54-R-15. California, USA.

  • Time period
    1 July 1982, 30 June 1983
  • Source
    Report
  • Both Western and Clarks?
    N
Count Type Range Max Year
Max Adults 101 to 500 110 1982-1983
Most Recent Adults 101 to 500 110 1982-1983
Max Nests 1 to 100 6 1982-1983
Most Recent Nests 1 to 100 6 1982-1983
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

Survey of nesting colony of Western Grebes at Clear Lake to assess extent of mercury contamination. Winter survey at Lake Berryessa as well but did not enter this due to non-breeding. No details on survey methods or when the counts were done. Also some historic information in this report: since 1949, chlorinated hydrocarbon pesticides have impacted grebe breeding success (Cook 1965, Herman et al. 1969) due to the presence of mercury ores and mines. Dead Western grebe specimens were collected and necropsied in 1982 and shown to be emaciated and with high concentration of mercury, possibly due to mercury levels in prey fish and lake substrate.

Survey Citation:
Suchanek, T.H., P.J. Richerson, D.C. Nelson, C.A. Eagles-Smith, D.W. Anderson, J.J. Cech, Jr., G. Schladow, R. Zierenberg, J.F. Mount, S.C. McHatton, D.G. Slotton, L.B. Webber, A.L. Bern and B.J. Swisher. 2002. Evaluating and managing a multiply-stressed ecosystem at Clear Lake, California: A holistic ecosystem approach. Managing for Healthy Ecosystems: Case Studies, CRC/Lewis Press. pp. 1233-1265 (in press).

  • Time period
    N/A
  • Source
    Book chapter
  • Both Western and Clarks?
    N
Count Type Range Max Year
Max Adults >1000 >2000 1949
Most Recent Adults 1 to 100 <50 1959
Max Nests 0 0 1958-1959
Most Recent Nests 0 0 1958-1959
Max Chicks 0 0 1958-1959
Most Recent Chicks 0 0 1958-1959

Comments:

This paper outlines the various stressors in Clear Lake throughout history and their impact on Western grebes and other species. DDD treatments to eradicate Clear Lake gnats were conducted in 1949, 1954, and 1957 which impacted nesting Western grebes (Herman et al. 1969). 100 dead grebes were found in 1954 and 75 dead grebes were found in 1957. In 1958, fish were tested and had very high DDD concentrations. There was a major crash in grebe breeding populations. Before 1949, there were over 1000 estimated pairs of breeding grebes on the lake. From 1958 to 1959, there were less than 25 pairs observed and no nesting nor chicks found (Hunt and Bischoff 1960). Concentrations of DDD were found to be about 80,000 to 85,000 fold higher in grebes than the surrounding water (Lindquist and Roth 1950, Rudd 1964) and this was the first evidence of bioaccumulation in food webs and delayed toxic symptoms of pesticide concentrations (Carson 1962, Rudd 1964). These grebes were declining at the same time of mercury mining in the 1950s yet no one at the time connected grebe declines to mercury concentrations. This paper was evaluating museum specimens of grebes from Clear Lake at that time to determine mercury levels then. The cycle of threadfin shad abundance and declines after their introduction to the lake also seems to have an effect of Western grebe populuations. Colwell et al. (1977) demonstrated a strong positive correlation between threadfin shad abundance and piscivorious birds including Western and Clark's grebes.

Survey Citation:
Hayes, F. E., B. J. McIntosh, D. G. Turner, and D. E. Weidemann. 2022. Historical and recent breeding of the Western Grebe and Clark's Grebe in a severely impaired ecosystem at Clear Lake, California. Monographs of the Western North American Naturalist 14:65-100.

  • Type
    shore; boat; air
  • Time period
    1938, 2019
  • Source
    Journal Article
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 >7500 2007, 2009
Most Recent Adults >1000 2746 2019
Max Nests >1000 5936 2014
Most Recent Nests >1000 2829 2019
Max Chicks 501 to 1000 599 2017
Most Recent Chicks 101 to 500 108 2019

Comments:

Summary of breeding population on Clear Lake in Table 1 from 1938 to 2010 and in Tables 2, 4, and 5 for 2010 to 2019 from various sources. He concludes that water level has no impact on reproductive success but has influence on nesting habitat availability. Win-generated waves inundated and destroyed approximately 35% of nests in a year and were a major threat of nests. Egg predation by avian and mammalian predators was also a cause of nest failure. Clear Lake has been particularly impacted by adverse anthropogenic activity such as acid mine drainage and mining activities that leached mercury into the lake, the use of dichlorodiphenyldichloroethane (DDD) to control Clear Lake gnat populations, introduced nonnative fishes, and the destruction of wetland habitats to development. This paper provides an extensive history of grebe monitoring and surveying over the years and the number of studies conducted at Clear Lake on grebes.

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.

  • Type
    boat
  • Time period
    13 June 2015, 27 September 2015
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 5077 2015
Most Recent Adults >1000 3253 2015
Max Nests 501 to 1000 888 2015
Most Recent Nests 501 to 1000 888 2015
Max Chicks 1 to 100 9 2015
Most Recent Chicks 1 to 100 9 2015

Comments:

Nests were mostly in open water. There are 21 colonies. Lowest reproduction in years. Two of the chicks were observed but nine chicks was an extrapolated number. Clear Lake is surveyed by Redbud Audubon. For the six lakes studied, 2015 was the fourth year of severe drought and nest success was not high.

Survey Citation:
Gericke, S. D. 2006. Exploring the effects of disturbance events on Western and Clark's Grebes (Aechmophorus occidentalis and A. clarkii) at Clear Lake, CA. MS Thesis, University of California, Davis. 70 pp.

  • Type
    boat; air
  • Time period
    3 May 2005, 16 September 2005
  • Source
    Thesis
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults >1000 presumably >1000 2005
Most Recent Adults >1000 presumably >1000 2005
Max Nests >1000 2550 2005
Most Recent Nests >1000 <2000 to 2550 2005
Max Chicks N/A N/A N/A
Most Recent Chicks N/A N/A N/A

Comments:

Clear Lake history of threats to grebes has been accounted for already so just added Gericke's findings regarding disturbances to breeding grebes in 2005 here. Nesting was observed at four nest sites, disturbances and grebe response was measured and quanitifed. Boats and aircraft resulted in the most frequest response from grebes but less so if non-motorized. However, non-human and non-seen disturbances caused the most responses by grebes. Disturbance source distance was the most significant variable to cause grebe response. Moderate and varied speed of boats and boats less than 10 meters from the colony were also major factors in grebe response. This study utilized opportunistic observations and had no control over sample size but had the advantage of observing grebes in real time disturbance events. Grebe nesting in isolated sites were less impacted by boat disturbances. However, some grebes still selected high disturbance sites because there might be some trade offs there, such as mammal predator avoidance of areas where human activity was higher. Though there may be some tolerance to human presence by grebes, human activity may limit full grebe population recovery and nesting potential. Establishing buffer zones around nesting areas would be a management action to protect grebe nesting activity.

Survey Citation:
Hayes, F.E., D.G. Turner, N.D. Zimmerly, M.B. Peralta, B.J. McIntosh, and M.E. Hellie. 2018. Egg destruction by males in the Western Grebe and Clark’s Grebe. Western Birds 49:258–269.

  • Time period
    2014, 2017
  • Source
    Journal 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:

Not a survey. First recorded observance of egg destruction by Western and Clark's grebes. From 2014 to 2017, four Western grebe and three Clark's grebe males destroyed eggs in nests at a late nesting stage at Clear Lake, California. The five eggs were in three nests that were recently vacated due to mammalian predation. It is unknown what the relation of these males were to the eggs they destroyed or whether it was interspecific or intraspecific. Since this was the first known observation of grebe egg destroying by grebes and was rare, this was not recorded as a threat to grebes but was included here as additional information.

Survey Citation:
Lawrence, G.E. 1950. The diving and feeding activity of the Western Grebe on the breeding grounds. Condor 52:3–16.

  • Time period
    April 1947, September 1947
  • 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:

Not a survey. Observations on the feeding habits of the Western grebe showed that their impact on game fish at Clear Lake is minimal despite claims otherwise. Stomach analysis of Western grebes demonstrated that they are not reducing numbers of black bass at the lake. However, grebes have been illegally killed by people who believe they are consuming large numbers of young bass. This entry records this as a threat.

Survey Citation:
Shuford, W.D., D.L. Thomson, D.M. Mauser, and J. Beckstrand. 2006. Abundance and distribution of nongame waterbirds in the Klamath Basin of Oregon and California from comprehensive surveys in 2003 and 2004. PRBO Conservation Science. Final report to U.S. Fish and Wildlife Service, Klamath Basin National Wildlife Refuge Complex,Tulelake, California, USA.

  • Type
    air
  • Time period
    9 June 2004, 16 June 2004
  • Source
    Report
  • Both Western and Clarks?
    Y
Count Type Range Max Year
Max Adults 1 to 100 41 2004
Most Recent Adults 1 to 100 41 2004
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:

Surveyed for 3 periods: spring migration, mid-breeding, and fall migration in 2004. Numbers here are just during mid-breeding season (June 9 to 16).

Sources of Information

  • Suchanek, T.H., P.J. Richerson, D.C. Nelson, C.A. Eagles-Smith, D.W. Anderson, J.J. Cech, Jr., G. Schladow, R. Zierenberg, J.F. Mount, S.C. McHatton, D.G. Slotton, L.B. Webber, A.L. Bern and B.J. Swisher. 2002. Evaluating and managing a multiply-stressed ecosystem at Clear Lake, California: A holistic ecosystem approach. "Managing For Healthy Ecosystems: Case Studies", CRC/Lewis Press. pp. 1233-1265 (in press); Feerer, J. L., and R. L. Garrett. 1977. Potential western grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 10.; Hayes, F. E., D. G. Turner, B. J. McIntosh, D. E. Weidemann, N. D. Zimmerly, M. B. Peralta, D. B. Stoppelmoor, and M. E. Hellie. 2018. Floating bird nests provide resources for wildlife: ecological roles of vertebrates using Aechmophorus grebe nests at Clear Lake, California. Wetlands Ecology and Management 26:1061–1072.; Ivey, G. L. 2004. Conservation Assessment and Management Plan for Breeding Western and Clark’s Grebes in California. 89.; 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.; Hayes, F. E., B. J. McIntosh, D. G. Turner, and D. E. Weidemann. 2022. Historical and recent breeding of the Western Grebe and Clark's Grebe in a severely impaired ecosystem at Clear Lake, California. Monographs of the Western North American Naturalist 14:65-100.; 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.
  • Feerer, J. L., and R. L. Garrett. 1977. Potential western grebe extiinction on California lakes. Cal-Neva Wildlife Transactions. 10.
  • Hayes, F. E., D. G. Turner, B. J. McIntosh, D. E. Weidemann, N. D. Zimmerly, M. B. Peralta, D. B. Stoppelmoor, and M. E. Hellie. 2018. Floating bird nests provide resources for wildlife: ecological roles of vertebrates using Aechmophorus grebe nests at Clear Lake, California. Wetlands Ecology and Management 26:1061–1072.
  • Ivey, G. L. 2004. Conservation Assessment and Management Plan for Breeding Western and Clark’s Grebes in California. 89.
  • 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.
  • Hayes, F. E., B. J. McIntosh, D. G. Turner, and D. E. Weidemann. 2022. Historical and recent breeding of the Western Grebe and Clark's Grebe in a severely impaired ecosystem at Clear Lake, California. Monographs of the Western North American Naturalist 14:65-100.
  • 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.
  • Clear Lake State Park
  • Clear Lake Information
  • Geographic Names Information System (GNIS)
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