|Clapper Rail, a tidal marsh bird. Photo © J. Schumacher/VIREO.|
A step. Another step. An orange bill probes deeply into the mud. A worm is extracted and eagerly consumed. A shadow passes overhead and the Clapper Rail dashes into the pickleweed, flashing its white tail. This is a special scene, as Clapper Rails, a federally endangered species, are few and far between in San Francisco Bay. What makes this particular scene extraordinary is that the marsh being probed by the Clapper Rail was diked farmland just ten years ago.
In 1994, the levee protecting 42.5 acres of farmland on the Petaluma River at the northern reaches of the San Francisco Bay Estuary was breached, and the Petaluma River Marsh was reborn. Commonly known as Carl's Marsh (named after Carl Wilcox of the California Department of Fish and Game (CDFG), who was indispensable in the marsh's creation), the restored tidal marsh was a collaboration between the Sonoma Land Trust and CDFG. It has been a success story.
Migrating shorebirds, such as sandpipers and Dunlin, flock to the site to feed on the mudflats and then slip into the vegetation to roost. Other species make the restored marsh a year-round home. These birds include waders such as Great Blue Herons and Great and Snowy egrets, as well as species especially reliant on tidal marsh habitat: Black Rails, Salt Marsh Common Yellowthroats, Song Sparrows, and Clapper Rails. Since 1999 PRBO has surveyed the marsh every spring, and since 2001 we have been conducting surveys year-round.
|An aerial photo time series of Petaluma River Marsh shows the progression from agricultural field to tidal marsh. Before the site was diked for agricultural use, it was a full tidal marsh with large mudflat areas along the Petaluma River. A--After the marsh was diked, a levee separated the Petaluma River from agricultural fields to the northeast. B--In 1995 the levee was breached in two locations to restore tidal action to the site. Because the pre-restoration elevation was below mean tide level, water and sediments came in with the tide and quickly created an unvegetated mudflat. C--By 1999, distinct tidal channels had formed and a few native cordgrass (Spartina foliosa) plants had become established, their seeds brought in with the tide. D--By 2004, the site was almost fully vegetated with a combination of cordgrass, pickleweed (Salicornia species) and alkali bulrush (Scirpus maritimus); and a higher-order channel network was already established.--Diana Stralberg|
We use several survey methods in order to characterize the diverse community of birds using the marsh. During the fall-spring migratory periods, we survey birds and identify species based on sightings, calls, and songs. During the breeding season (March-July), biologists also monitor breeding activities, using two intensive methods. The first is spot-mapping or mapping territory boundaries for all birds breeding in the marsh. Biologists observe the behavior of a pair of birds and, based on their actions and interactions with neighbors, are able to map the location, boundaries, and number of territories in an area (map E above). Territories provide a key measure by which we determine how many birds actually breed in an area, as locating nests can be very difficult: it is not uncommon for a biologist to discover just a single nest in an entire day of searching. After all, the breeding birds are trying hard not to be found!
At Petaluma River Marsh, Song Sparrows are the predominant breeders, so our work has emphasized this species. Samuel's Song Sparrows, a subspecies endemic to tidal marshes around San Pablo Bay (Observer 128, Spring 2002), had already colonized the outer levee when the first avian surveys were conducted in 1998; they were confirmed breeding that year.
|How well does tidal marsh habitat undergoing restoration support vulnerable Song Sparrow populations? Photo © F. Truslow/VIREO|
In 2004, PRBO biologists went beyond recording the precise locations where male Song Sparrows sing to map territorial boundaries. We implemented a second, more intensive method --nest-finding and -monitoring. PRBO has applied this method of tracking the reproductive success of breeding birds (developed at the Palomarin Field Station) to studies of tidal marsh birds in the mature marshes of the San Francisco Estuary since 1996.
|In map E above, Song Sparrow territories are shown with black outlines. Nest fates are indicated with red symbols: (circle) a successful nest, one that fledged young; (trianble) a nest that failed.|
Reproductive success of birds breeding in recently restored tidal marsh habitat had not been well studied until PRBO's newest work commenced in 2004. It is part of a large, $3.7 million, multi-year, multi-disciplinary effort called Integrated Regional Wetlands Monitoring (see page 5). To supplement our studies at mature marsh sites (China Camp, Rush Ranch, and Benicia State Park among them), last year we began studying birds' reproductive success at Petaluma River Marsh and a former salt pond near the Napa River where levees were breached in 1996. In 2004 at Petaluma River Marsh we found a total of 75 Song Sparrow nests whose ultimate fate (success or failure) we could determine (map E). Of these, 65 nests were abandoned or depredated. The percentage of successful nests was about half of that found in older marshes around San Pablo Bay, possibly related to sparser vegetation associated with the youth of the marsh.
Continuing these studies with our collaborators in 2005 will help us address the question of whether Song Sparrows and other marsh-dependent birds are able to reap the benefits of recently restored marsh habitat.
One step at a time--following secretive birds such as the Clapper Rail or the more ubiquitous Song Sparrow--we hope to ultimately determine how tidal marsh restoration can best support the recovery of depleted populations.