Date: 7/11/19 5:31 pm From: Bill Bousman <barlowi...> Subject: Re: [southbaybirds] 30 Yellow-billed Magpies on Monument Peak
David and all,
Magpies do flock on occasion, more often in winter. The Santa Clara County Notebooks have about 11 records of 50 or more birds found in a day. John Mariani has had the two highest counts, both in 2002. He recorded 123 at Calero Reservoir on a Big Sit he did on 10/13/02 and later in the year noted 114 coming to a roost there on 11/23/02. Ryan Phillips counted between 88 and 108 on Laguna Avenue in Coyote Valley about 12/13/09 (just over the ridge from Calero Reservoir).
The Mount Hamilton CBC has reported sizeable concentrations in some years. Mike Rogers and Mike Mammoser counted 80 in Isabel Valley on 12/28/08. Mike Rogers keeps meticulous notes and may have higher counts in the many years he has done that sector (or perhaps from the records that the late Don Schmoldt bequeathed to him). I counted in San Antonio Valley on the Mount Hamilton CBC count from 1980 to 2015 and my highest tally was of 62 birds on 12/22/99. Based on my own experience there, it seemed to me that the birds were patchy in their distribution and moved around a lot. If you missed one or two flocks, your numbers were down for the day.
Jean Linsdale wrote a monograph (Linsdale, J. M.1937./The Natural History of Magpies/.Pacific Coast Avifauna, No. 25, Cooper Ornith. Club) and you can read this on SORA or download it. He did much of his field work in Santa Clara County. W. E. Unglish of Gilroy told him in the early 1930's that he had seen a flock of about 200 birds in the southern Santa Clara Valley, certainly an exceptional count. Numbers in those years suffered from ground squirrel poisoning campaigns according to Linsdale. I hope there is less of that nowadays, and certainly not on open space lands.
Bill Bousman Menlo Park
On 7/8/2019 5:16 PM, dvdovalina via Groups.Io wrote: > There were several flocks of Yellow-billed Magpies flying from one > rock outcrop to another along the ridge about 0.5 miles south of > Monument Peak. I counted thirty birds in the largest congregation > (murder?). They probably came up to the ridge from the Calaveras > Reservoir valley as they eventually flew off in that direction. Is it > common to have such large flocks? You definitely see it with other > corvids, but this is the first I've seen magpies in such numbers. >
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