Lake Berryessa

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 Lake Berryessa, 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:
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 Unpublished technical report.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
  air
• Time period
  1982, 5 August 2003
• Source
  Conservation Assessment, Management Plan
• Both Western and Clarks?
  N/A

Count Type	Range	Max	Year
Max Adults	1 to 100	presence	1982, 1990s, 2003?
Most Recent Adults	1 to 100	presence?	2003
Max Nests	1 to 100	presence	1990s
Most Recent Nests	1 to 100	presence	1990s
Max Chicks	N/A	N/A	N/A
Most Recent Chicks	N/A	N/A	N/A

Comments:

This entry to capture historical record and an aircraft survey in 2003. There were breeding grebes and noted as a colony site in Lake Berryessa in the 1990s, no numbers or other details. Source is D. Anderson, pers. comm. On August 5, 2003, an aircraft survyed Central Valley lakes for colonies for which there were recent grebe sightings or possible habitat but no data on what was found, if anything, for this lake. In 1982, liver samples taken from 8 dead Western grebes had high mercury concentrations (Litrell 1991).

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
  11 July 2007
• Source
  Report
• Both Western and Clarks?
  Y

Count Type	Range	Max	Year
Max Adults	101 to 500	200	2007
Most Recent Adults	101 to 500	200	2007
Max Nests	N/A	N/A	N/A
Most Recent Nests	N/A	N/A	N/A
Max Chicks	0	0	2007
Most Recent Chicks	0	0	2007

Comments:

No nesting habitat was available, water level was below nesting vegetation. No nests nor chicks were observed despite having supported nesting grebes historically. Subsequent reports have their own entries.