McNabney Marsh Shorebird Nesting Raft Project

Since the operation of the tide gates by EcoServices in 2009, much of the suitable ground nesting habitat in McNabney Marsh has been lost in the 138-acre wetland. Because of subsidence (sinking of the marsh plain) and a constriction at the Union Pacific Railroad Bridge on Peyton Slough, McNabney Marsh doesn’t adequately drain when the tide gates are open. With these constraints, tide gate operations create challenges for ground-nesting shorebirds and waterfowl which have depended upon McNabney Marsh for decades. During high water events nests are flooded, and eggs and nestlings are lost.

Because waterfowl usually nest in heavily vegetated areas that are not easily reproduced on floating rafts, MVSD decided to focus on creating nesting habitat for shorebirds: American Avocet, Black-necked Stilt, and Killdeer. Between February 2015 and March 2016, MVSD built and installed 16, 4’x10’ nesting rafts in McNabney Marsh. The rafts were joined together into three different sized structures: 4’x10’, 8’x10’ and 8’x20’. The surface of the rafts were covered with sand, gravel, and rock to attract the desired species.

Much of the labor for this project was provided by volunteers from the California Department of Fish and Wildlife Natural Resources Volunteers and the Mount Diablo Audubon Society. Funding for materials and supplies for the rafts were donated by:

  • Plains Products Terminals
  • Republic Services
  • The Wildlife Project

Grant funds were provided by:

  • Audubon California
  • Contra Costa County Fish and Wildlife Committee
  • Mount Diablo Audubon Society

MVSD staff and consultants have been closely monitoring the nesting rafts since March 2016 and it is clear that the structures are working for both the avocets and the stilts. The following statistics summarize the success for the project for the 2016 nesting season:

  • 14 nests on 16 rafts (8 separate structures)
  • 11 American Avocet (AMAV) nests
  • 3 Black-necked Stilt (BNST) nests
  • The AMAV nested between 4/25/2016 and 7/5/2016
  • BNST nested between 4/25/2016 and 5/20/2016
  • Both species started nesting one month earlier than in 2015
  • AMAV fledged about 12 young in 2016
  • BNST fledged about 6 young in 2016

To learn more about this project contact the District Biologist at kdavidson@mvsd.org.