Date: 1/5/21 4:10 pm
From: Bill Bousman <barlowi...>
Subject: Re: [southbaybirds] 910 Bonaparte's Gulls at Palo Alto Baylands on January 1

Most years, Bonaparte's Gull flock numbers are relatively small, in the
low 100's.  Adam's observation is similar to those of prior years of
very large flocks or concentrations that show up irregularly, for
reasons that are not obvious to me.  I've attached a graph of single day
maximum counts from 1993 to 2018 that I've taken from the county
notebooks.  The highest was of 1900 birds in closed Alviso salt ponds
recorded on 11/16/93 by Mike Rogers.  The second highest was of 1700
birds in the Palo Alto estuary on 11/27/02 by Mike Mammoser.  For this
species, the major role in the county appears to be a fall passage from
the beginning of November through mid-December.  The flock Adam reported
is about two weeks late based on the data from prior years.

Bill Bousman
Menlo Park

On 1/4/2021 10:48 PM, Adam Burnett wrote:
> One of the highlights of my New Year’s birding was a flock of at least
> 910 Bonaparte’s Gulls, seen from about 2:45-3:00 PM on January 1. I
> was standing by the edge of the Palo Alto Duck Pond, and I saw the
> flock in flight above the water treatment plant to the south. When I
> first saw this swirling flock in the distance, I expected them to be
> starlings! Binocular views revealed them to be Bonaparte’s Gulls, and
> for the next 15 minutes or so, groups peeled off and flew northeast
> across the bay. I assume they were headed to a roosting spot, as Bill
> Bousman mentioned in his posts on 11/5/14 and 12/2/19.
> Apologies for the late post, but zooming in and meticulously counting
> the birds in my photo took quite a while! The attached photo shows 820
> birds, with more of the flock cut off at the right side of the frame.
> An additional group of 90 birds had already departed across the bay,
> for a total of at least 910. As they streamed overhead, I biked to the
> T-intersection of Embarcadero Road and had much closer views of the
> flock, but I didn’t see any other species mixed in, neither any common
> larger gulls nor any rarities like Black-headed or Little. Regardless,
> it was an amazing spectacle! I regularly see flocks of around 100
> Bonaparte’s Gulls above the water treatment plant, best viewed from
> the west edge of Byxbee Park, but I had never seen numbers like these.
> Other highlights from a full day of bike-birding on January 1 included
> a male EURASIAN X AMERICAN WIGEON HYBRID with American Wigeon on Pond
> A1, and the continuing ROCK WREN at Byxbee Park, hanging out around
> the small fenced area at the west edge of the park, opposite the south
> corner of the water treatment plant. Yesterday, January 3, I visited
> the 3 wintering CHIPPING SPARROWS at Terman Park in Palo Alto, after
> one individual was reported there by Alex Tey and Ann Hepenstal on the
> Palo Alto CBC.
> Happy birding in 2021!
> Adam Burnett

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