Re: Where are the Lake Merritt Scaup?

Bill Bousman

Jim and others,

I don't know if some of the numbers from the South Bay help, we do have a lot of scaup that winter there.

Please excuse me for my wonkish analyses (or just delete).  I've attached a .png figure that you should be able to see on your computer.  I have been engaged since the 1990s looking at temporal data (translation, when are bird here and when not).  What I show in this figure are the cumulative sightings for two locations in Santa Clara County.  The first data set is Alviso Slough Trail (which surrounds Pond A9 through A15 in Alviso).  That dataset is from 2007-16; the highest daily count was 6672 scaup on 29 Oct 2009.  The second data set is the rest of the South Bay in Santa Clara County, including the Alviso ponds, but there is no duplication of the Alviso ponds survey dates.  The second dataset has sightings from 1993-2016; the highest daily count was 22,500 scaup on 24 Dec 2000.  I use the word "sighting" to indicate how many birds are found in one day, that is, if I tally 3,000 scaup (here I group all Greaters, all Lessers, and all not identified to species), then that means I had 3,000 sightings.  A week later I may have recorded more or less sightings and I add them to the dataset.  So for the figure here, the total number of scaup sightings is 154,536 sightings over the time period.

The data show that most scaup have been recorded arriving in the first or second week of October and their numbers remain constant until the first week in February (the linear regression line has an r^2 value of 0.99).  There is a "break" at the beginning of February and wintering birds continue to be seen, but only at 15% of the fall and early winter rate.  My inference is that the fall birds arrive pretty much at one time in early October, most leave in early February, but some remain towards the end of March.  But these are just numbers.  I may believe my inference, but there may be far more going on than I can see from these data.

Bill Bousman
Menlo Park

On 2/16/2021 5:29 PM, Jim Chiropolos wrote:
Work took me to lake Merritt today and I looked at the lake from two areas quickly and saw less than 60 scaup. Intrigued, I looked at ebird Lake Merritt sightings this month and I think the high scaup number (both lessor and greater) is 100 and for the winter 250 or so (one report - thanks Alex). The areas I looked included two of the three spots the large flock usually was. Past years, I think the lake, would hold a flock of 250 to 500 or so all winter (guess on my part)

So, I ask the question? Did I miss the big scalp flock since I did not scan the entire lake?

Or is the flock not there as the eBird reports - or do people just look for the barrows goldeneye and then are done - but has anyone birded  the entire lake to establish the scaup flock size?
I worry that maybe one of the following could be occurring:
1. Lake Merritt is changing and the habitat is not holding scalp as it used to.
2. Scaup numbers overall are down - I don't bird the waterfront much these days so I do not have a sense of scaup numbers on the bay 
3. Scaup are not using the lake in February

Does anyone have historical scaup flock sizes for lake merritt so we can track the flock size and where we are this year. Lake Merritt is one of the birding gems of the east bay and it would be good to know the scaup flock size as they are one of the "keystone" wintering species for the lake.

If anyone does a comprehensive scalp lake survey - can you send me your totals offline in response to this post? IT probably would be  good to note it as a comprehensive lake survey in the ebird list comments - we need one of these at least every year and month if someone uses the lake as a local patch - its too far from home for me.....

I did see 8 red-breasted mergansers on the lake and I think this is a high end number for this species on the lake. I like seeing big scaup flocks on the lake in winter. This is where I learned to recognize greater scaup from lessor scalp by the  nature center so it is a special place for me (and there still is a mixed group of greater and lessor scaup coming in for food.....).

Jim Chiropolos

( PS on  the topic of decreasing duck numbers I did not look for Barrows Goldeneyes in the channel but it has saddened me how from over 10 or more using Barrows Goldeneye were present in the winter in the channel about 10 years ago we are maybe down to one pair or so with numbers seemingly decreasing every year . The Merritt channel human habitat is very different from 10 years ago...…)

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