PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 150, Fall 2007: Units of Conservation: Single Species to Ecosystems



Rails, Predators, and Birders

Waldo's Dike

Rich Stallcup

Units of Conservation
Glossary of Terms
CEO's column
Snowy Plovers and Sandy Coastline
Sierran Forest Focal Birds
Marine Ecosystem Research
Ecosystem-based Management
PRBO News and Highlights
Remembering Bob Mayer
Focus on Black Rail Habitat
Latin American Intern Story
Bird-A-Thon 2007
The Grand List

Aerial view of Tomales Bay wetlands reveals the mile-long levee (paler than the surrounding ground), running laterally near the bottom of the photo. © Robert Campbell / Point Reyes and the San Andreas Fault Zone, with aerial photos by Robert Campbell and text by Frank Binney, is due out soon from Chamois Moon Press.

The birding history of an area often tells a parallel story—of bird populations and their changing conservation needs. Over the past four decades, people exploring a man-made levee on the upper reaches of Tomales Bay, in search of a tiny, rare marsh bird, have witnessed the changing threats it faces and, recently, a promise of new protection.

Winter 1974—We are walking at dawn near the south end of Tomales Bay, on the massive dike constructed in 1946 by the Giacomini dairy to create 550 acres of Holstein pasture. Waldo Giacomini owned the ranch from the 1960s until the land was purchased by Point Reyes National Seashore in 2000. Early access to what I called "Waldo's Dike" was denied to all but hunters and a couple of ornithologists—to census rails.

A huge high tide is approaching, and there has been a lot of rain. The isolated salt marsh is nearly inundated, and the creatures that usually shelter here all scurry, swim, or fly for higher ground. We are searching for Clapper Rails, trying to determine if they have a resident population in West Marin (within the year we document they do not.)

Rails are elusive, ground-dwelling marsh birds of thick, low, wetland vegetation. Although the habitat here supported Black and Yellow rails into the early 20th century, earthquakes and human tampering had so changed the natural systems that we were quite astonished on that day in 1974 to see seven Black Rails.

Since that discovery in the late 1970s, many birders have been keeping informal track of the rail situation at Waldo's Dike. A 68 high tide is minimum for hopes of seeing rails, whose hiding places are flooded then. Over time, I have seen the Black Rail more than 200 times, and others have spotted more. In 1984, I saw the first Yellow Rail recorded there in 75 years; since then, 13 have been found. A very few Virginia Rails and Soras are usually seen on a ‘good' day, and Clapper Rail has occurred twice in 30 years.
Rich holds a Black Rail rescued from predators. Photo by Jack Swenson.

In that same time span, predation on rails displaced by high tides has grown extreme. Regional protection for egret and heron populations over the past 40 years has resulted in increased abundance for these big waders—some of which have pioneered foraging opportunities beyond fish and frogs. More and more of them hunt burrowing mammals in dry fields, and many have learned the advantages of attending high tides at altered landscapes. Of the 200 Black Rails I have seen at Waldo's Dike, 143 have been killed and eaten, most by Great Egrets.

The egrets may search ‘islands' of pickleweed and gumplant and jab the small birds on the ground. More often, the rails are flushed into flight by rising water, overtaken by the faster, larger assailant, and snapped from the air. Birders on the levee, pointing and exclaiming, sometimes cause the predators to turn back.
Birders align on Waldo's Dike. Photo by Rich Stallcup.

Winter 2006—At a dawn high tide on the same massive levee, now publicly owned, 77 telescopes stand on the berm. Over the next few years, the National Park Service will restore much of the pasture to tidal wetland. Waldo's Dike will come down (see For birders, seeing the rare rails at the south end of Tomales Bay will become nearly impossible then. For the birds, survival will become much easier: rails will be able to walk away from rising tides to higher ground and stay concealed beneath plants—the way it was before the habitat alterations of 60 years ago.

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