Point Reyes Bird Observatory, Observer 108

Program Notes

Conservation through Science


PRBO's recent work, surveyed here in part, reflects our newly crafted mission statement.

Notes from PRBO's Program:
  • Terrestrial Program

  • Marine and Farallon Program

  • Coastal and Estuarine Research

  • Latin American Research




  • Terrestrial Program


    Tidal marsh birds

    Funding from the National Biological Service enabled PRBO in 1996 to begin assessing populations of birds that rely on tidal marsh habitats in San Francisco Bay. Biologists Nadav Nur, Geoff Geupel, and research associate Steve Zack are heading up the project, with assistance from Tom Gardali. This spring and summer, we censused three endemic subspecies of Song Sparrow and one of Common Yellowthroat, as well as Black Rails (see below), at 20 sites around the bay. At four sites in the northern bays, we also investigated the songbirds' nesting biology. This effort will lead to the first- ever quantitative assessments of bird populations that, for several years, have been considered endangered but remain insufficiently studied to list for federal protection. It also adds to PRBO's base for contributing avian research to a broad regional effort aimed at restoring remnant marshes on San Francisco Bay.

    California Black Rail

    Are Black Rails maintaining their populations in the remnant salt marshes of northern San Francisco Bay? Or do they and other species in similarly narrow niches require large tracts of contiguous marsh habitat for their populations to persist over time? As part of the new study described above, PRBO research associate Jules Evens directed field work in 1996 to compare local abundances of Black Rails with estimates we obtained in 1986-88. Rails were present this year at 20 sites (of 22 surveyed). About half the sites had higher densities than were detected in 1988, 25% supported similar densities, and 25% had lower densities. The two sites where rails had disappeared in the years between 1988 and 1996 were small, discrete marshes that formerly supported very small populations. The higher densities detected in 1996 were generally found at larger sites, suggesting that the areal extent of the habitat, and perhaps annual rainfall, determine rail densities at a given site. Final results from this study will provide the quantitative base for management decisions that include Black Rails in the future equation for San Francisco Bay.

    Central Valley Songbirds

    PRBO is contributing data on bird populations which The Nature Conservancy (TNC) has adopted as a measure of habitat restoration. At its Cosumnes River and Stony Creek preserves, TNC is testing methods for restoring riparian habitat (severely reduced and degraded throughout the Central Valley). PRBO's team of biologists and interns, led by Geoff Geupel and Nadav Nur, recently found that natural flooding is a key factor in songbird population recovery. Stream overflow events in the wet season of 1995 led to increased nest success and diversity the next spring. Breeding birds found abundant leafy plant growth for concealing their nests from predators in new vegetation seeded and nourished by the flooding. Our conclusions helped TNC decide to purposely break a dike at Cosumnes in the spring of 1996 - a passive method for restoring riparian habitat, without expensive tree planting efforts. By continuing this project, PRBO aims to produce recommendations for effectively restoring riparian habitats on a broad scale.



    Marine and Farallon Island Program


    Storm-petrel decline

    Of the Ashy Storm-petrel's worldwide population, some 60% breeds at Southeast Farallon Island (SEFI). Concerned that the Farallon population of this diminutive relative of albatrosses might warrant federal listing as "threatened," PRBO this year prepared a new analysis of the Ashy's status at the island. Comparing 1971-72 estimates of its breeding population on SEFI with data obtained in 1992, we found an overall population decline of about 35% over the 20-year period and a decline in breeding birds of about 40%. According to Farallon research director Bill Sydeman, the actual amount of the decrease is uncertain, due to factors including oceanographic differences (which likely affect storm-petrels' breeding) between 1972 and 1992. Our recommendations include a call for further research on the Ashy's population size and status and also planning a recovery program that might employ nest boxes (see Observer 107) to enhance the birds' nesting success and help secure important breeding grounds for the Ashy Storm-petrel at SEFI.


    Contaminant findings

    In July 1996, we submitted to the Gulf of the Farallones National Marine Sanctuary our final report on levels of organochlorine pesticides and trace metals found in seabirds, marine mammals, and their prey. Major findings: highly elevated levels in northern sea lions (less so in Common Murres) of DDE and PCBs; and moderately high levels of mercury in sea lions and Pigeon Guillemots. Although murres and sea lions appear to be subject to elevated contaminant loads, the levels have decreased substantially over the past 20 years. Copies of the report (of which chapters are being published in scientific journals) are available from PRBO for $40.


    Alcatraz Island

    Under a recently completed long-term cooperative agreement with Golden Gate National Recreation Area, PRBO has begun monitoring seabird populations on Alcatraz Island. Biologist Nathan Fairman visited "The Rock" throughout the breeding season, focusing on Brandt's and Pelagic cormorants, Western Gulls, Black Oystercatchers, and Pigeon Guillemots. The Brandt's Cormorant colony, newly established in 1993, already contains over 200 breeding pairs, and reproductive success for this species was considerably higher on Alcatraz this year than it was on SEFI, suggesting that the birds in San Francisco Bay have found a new and reliable food source. Goals for this ongoing project include assessing the influence of human disturbance on the cormorants and other wildlife: more than a million people currently visit Alcatraz each year!

    Oil Spill Seabird Restoration

    We initiated studies in 1996 on SEFI as part of a $5 million settlement for damages from the Apex Houston oil spill (see Observer 101, Fall 1994). Our aim is to help assess population trends for the Common Murre in California and elsewhere along the west coast, and to interpret a restoration effort at Devil's Slide Rock being conducted by the U.S. Fish and Wildlife Service (USFWS). PRBO's role, carried out by Farallon biologist Michelle Hester and project directors Bill Sydeman and Nadav Nur, will include investigating year-round murre colony attendance patterns, developing correction factors to convert counts of individuals to estimates of breeding pairs, and other activity. As in the past, our commitment to long-term research in cooperation with USFWS on the Farallones forms the backbone of this project: it enables us to understand seabirds population changes in relation to variability in the marine environment.




    Coastal and Estuarine Research


    Snowy Plovers at Point Reyes

    Due primarily to PRBO's effort to protect and monitor nest sites, Snowy Plovers at Point Reyes National Seashore fledged four times as many chicks in 1996 as in 1995. In a project supported by PRBO members, staff biologist Catherine Hickey and coastal program director Gary Page worked with the Park Service to place exclosures around plover nests.

    These prevented predators such as the Common Raven from taking the plovers' eggs. Signs on the beach helped educate people about the birds' vulnerability to disturbance. Fifteen chicks reached fledging compared with only four in 1995. PRBO gained experience protecting a threatened species and strengthened our partnership with the National Park Service. We will continue this effort to both increase the number of locally nesting Snowy Plovers above the point of no return and to evaluate management techniques that can help the species recover.

    Snowy Plovers at Moss Landing

    New records were set in 1996 in our long-term study of Snowy Plovers in the Monterey Bay area. Approximately 365 chicks hatched, about 75 more than in 1995, and approximately 141 fledged, compared to a previous high of 120 (these findings are preliminary). The increase is due in part to continuing collaborative efforts, by PRBO and several public agencies, to use exclosures to protect Snowy Plover nests from predators. Also, a new management effort in 1996 at Moss Landing, spearheaded by PRBO staff biologist Doug George, succeeded dramatically. With the permission of California Department of Fish and Game, we manipulated water levels in the salt ponds to produce the highest quality habitat for plover nesting and brood survival. Of the 141 Snowy Plover fledglings from Monterey Bay area, 59 came from successful nests at Moss Landing salt ponds. The new methods are adding to our ability to take effective action for the recovery of a native nesting shorebird.




    Latin America


    Bird Conservation and Genetics

    In a project developed jointly with San Francisco State University (SFSU), PRBO is investigating where in the tropics various populations of North American breeding birds spend the winter. Collaborating with Dr. Tom Smith, a PRBO board memeber and scientist with the SFSU Conservation Genetics Laboratory, we use genetic markers to discern slight differences in the makeup of bird populations. Determining which of California's migratory songbirds winter in the dry tropical forests of western Mexico, the highlands of Honduras, or the Costa Rican cloud forests will greatly advance our understanding of the demographic factors that regulate these populations, both in the breeding and wintering grounds. Our 1996-97 project will utilize student field biologists from El Salvador and Honduras, providing them with intensive training in bird identification and mist-netting techniques.

    Training in Yucatan

    Building on successful programs in Mexico, Costa Rica, and Panama, this winter PRBO will lead a course in the Yucatan for Latin American students and technicians, the first such training offered in southeastern Mexico. Collaborating with the Canadian Wildlife Service and Universidad de Campeche, PRBO biologist Borja Mil&aagrave; will help direct the two-week course at Calakmul Biosphere Reserve in the southern Yucatan peninsula.

    Las Joyas Volunteers

    Starting in mid-November 1996, experienced PRBO field biologists are volunteering for three months at Mexico's Las Joyas Field Station (see Observer 106). assisting in avian monitoring efforts at Sierra de Manatlán Reserve. Support for this international exchange of expertise came from our generous sponsors who pledged contributions to Rich Stallcup's Bird-a-Thon count this year. Muchas gracias!

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