Western Snowy Plovers (Part IV): Population Change

Part IV – Population Fluctuations

As described previously, Western Snowy Plovers (WSP) wintering on Pacific beaches are extremely faithful to their roosting sites and are rarely seen outside their immediate vicinity, even as little as a few hundred yards down the beach. Northern Zuma Beach consistently has the largest wintering flock of  WSPs, averaging 46% of total county birds, followed by Surfrider and Santa Monica Beaches with 14% each.

By recording bands, we discovered that there is some back-and-forth movement between Zuma, Surfrider and Santa Monica flocks. Of L.A. County’s approximately 75 miles of beach, Snowies confine themselves almost entirely to only 1.2 miles, 1.6% of the total linear beachfront. Ryan Ecological Consulting (Feb. 2010 & Nov. 2010) suggested that conservation efforts be focused on these areas, an opinion with which I heartily concur.

California’s population of WSPs fluctuates significantly seasonally and yearly:

Year    Summer         Winter           New Birds      LAC Winter  Surfrider
2005    1680                4261                2581                334                  12
2006    1719                3546                1827                196                  34
2007    1362                3290                1928                200                  37
2008    1394                3205                1811                233                  36
2009    1405                3379                1974                244                  37
2010    1591                3744                2153                211                  47
2011    1715                3763                2048                326                  78
Ave.    1552                3598                2046                249                  40

Summer: Adult WSPs counted on the California breeding grounds.
Winter: Total Calif. birds found during the following January’s Winter Window Census.
New Birds: Wintering population of young WSPs fledged that summer on the coast, plus inland race Snowy Plovers spending winter on California beaches.
LAC Winter: Total birds counted in L.A. County on the Winter Window Census.
Surfrider: Total birds at Surfrider Beach on the Winter Window Census.

From this information, we can easily draw these conclusions:
2006-07 Winter population declined 17% from the prior winter
2007 breeding population declined 21% from the prior summer
2007-08 Winter population declined 7% from the prior winter
2008-09 Winter population declined 2.6% from prior winter
2011 breeding population has rebounded to its 2006 level
2011-12 Winter populations are still down 12% from 2005

No solid reason was ever determined for the declines. Some researchers think a Winter cold snap might have caused the initial decline in 2006-07; other researchers disagree, saying they’d already seen a decline in returning birds in Fall, 2006.

The Los Angeles County wintering population fluctuates between about 200-330 birds, averaging about 7% of the total California Snowy Plover Winter population. For the sake of comparison, this is about 2% of Malibu’s 2010 human population of 12,645.

The highest count ever recorded for Surfrider Beach was 81 birds on Jan. 22, 2012.  This count included one banded bird GG:AR (left green over green, right aqua over red), one of three birds banded at Oceano Dunes near Pismo Beach in Summer 2012, first appearing at Surfrider on Sep. 25, 2012 and reappearing on Christmas Day, Dec. 25, 2012. Upward trends are heartening to see, but unexpected downturns can always reoccur.