The decline of Mountain Plovers in two graphs

I live in Yolo County, California, near Sacramento, where Mountain Plovers used to be an annual winter specialty. Searching for “dirt clods with legs”, we used to be able to find dozens of these unique shorebirds, sometimes over a hundred.

Those days are over. They are now “irregular”, meaning we don’t find them every year. We’ve struck out five of the last eleven years. Before that, we averaged a high count of 72 individuals. The first graph, built from records in the Yolo Audubon Society newsletter, emails to the Central Valley Birds listserv, and eBird, shows the high count each winter in Yolo County.



This second graph backs out a bit in space and time, looking at all Mountain Plovers worldwide, starting in 1980. They are a bird of the steppe, breeding mostly on the Great Plains between the Rockies and the flat lands, between the Canadian and Mexican borders. They winter in open country in a vast arc west and south of there, mostly in California, Arizona, New Mexico, and Texas.

MOPL cbc

All the Christmas Bird Counts nationwide, plus Mexico, averaged 728 birds per count thru 1994, but have never hit that mark since. Fewer than 200 individuals have been enumerated six of the last ten years. Adjusted for party hours, the graph basically looks the same.

Fall Migration in the Central Valley

warblers fall 2018In 2010, after ten years of collecting data on morning “warbler walks” in my local patch, the Central Valley Bird Club Bulletin published my results. You can read the whole paper here:

Hampton, S. 2010. Passerine migration patterns in Davis, Yolo County—2000-2010. Central Valley Bird Club Bulletin 13(3): 45-61.


Bay Area birders are surprised when I tell them Willow Flycatchers and MacGillivray’s Warblers (above) are daily in fall migration in Davis.

It begins with this:
“Although passerine migration may conjure images of Point Reyes for many local birders, the Central Valley, with its north-south orientation, is believed to be the primary migration corridor through California for most species, surpassing the coastline in this regard (Humple and Geupel 2002).”


Here, I’ve re-visualized my results for fall migration in two simple graphs, one for more common species (peaking at 2 to 13 birds per survey), and another for less common migrants (around 1 or less per survey).




A few caveats:

  • A “survey” here is basically a morning walk lasting about 35 minutes.
    This was for my little route in north Davis. For other locations in the Central Valley, even nearby ones, I would expect the numbers and relative abundance to vary a little. For example, I see a lot more flycatchers at Babel Slough and Grasslands Park than are reflected here.
  • Putah Creek near Pedrick Rd, a current favorite of birders, generally has more birds than is shown here because it’s a larger area, birders spend more than 35 minutes when they visit, and the habitat is slightly different. It seems better at holding fall migrants for more days, making their detection more likely.
  • On these new graphs, I’ve left out the rarer birds, species that occur at a rate of less than 0.2 birds/survey (less than 1 out of every 5 surveys).
  • A large portion of the birds in my data are “heard only”.
  • For spring migration and additional details, see the full article linked above.

This last graph provides a cumulative view of all the migrants at once. Peak diversity is in late August. After that, the Yellow Warblers take over. After that, not shown here, the Yellow-rumped Warblers, both Audubon’s and Myrtle, arrive, signalling the end of fall migration.


It would be interesting to compare these relative abundances and timing with more recent eBird data, both in north Davis (where the eBird hotspot for this survey area is “North Davis Farms Subdivision”) as well as other locations in the Central Valley. Have at it. I’m happy to provide my Excel spreadsheets of this data to anyone interested.