The waters of the Monterey Bay National Marine Sanctuary are heavily used by seabirds and shorebirds, for many reasons:
- Upwelling that originates off Davenport and Point Sur provides feeding grounds that are rich in small fishes such as anchovies and sardines.
- The land surrounding these waters serves as nesting habitat for many species.
- The sanctuary is a convenient stop-off point for many migrating birds that come from as far away as Chile, New Zealand, Hawaii and Alaska.
Ninety-four seabird species are known to occur regularly within and in the vicinity of the sanctuary; among these, about 30 are dominant. In addition, approximately 90 tidal and wetland species occur on the shores, marshes and estuaries bordering on the sanctuary, about 30 of which are dominant. Species composition overlaps little between the tidal/wetlands and ocean habitats, except for some species of grebes, loons and ducks.
Water depth and distance to the shelf-break front are the most critical factors determining habitat use by seabirds:
- Very deep water lies within a few kilometers of shore near Moss Landing and Davenport, as a result of the presence of the Monterey and Ascension Submarine Canyons, respectively. These deep waters are populated with “pelagic” birds, such as Black-Footed Albatross, Ashy Storm-Petrel and Xantus’ Murrelet, during summer and fall – and with Northern Fulmars and Black-Legged Kittiwakes during winter and spring.
- The coastal avifauna, found over the continental shelf, is composed largely of Sooty Shearwaters, Western Grebes, Pacific Loons, Brown Pelicans, cormorants, Western Gulls and Common Murres.
- Very close to shore, usually near the breakers, are Surf and White-Winged Scoters and Marbled Murrelets.
The vast majority of seabird species in the sanctuary are seasonal visitors. Most species are seasonally resident and come in large numbers from temperate areas of New Zealand and Chile as well as Hawaii, Mexico and Alaska to winter in sanctuary waters. They exploit the rich prey resources of the area, which is located in the central upwelling region of the California Current system. The prevalence of marine birds using sanctuary waters changes from year to year, due to fluctuations in marine conditions, especially related to El Niño.
The shoreline and coastal wetlands that border the sanctuary are also important to birds. Elkhorn Slough attracts the third largest concentration of shorebirds in California, surpassed only by the much larger Humboldt and San Francisco Bays.
The dominant shorebird species on the intertidal mudflats of Elkhorn Slough and the Salinas River mouth are sandpipers, Dunlins, Sanderlings, dowitchers, Black-Bellied Plover, Willets, American Avocets, Marbled Godwits and Long-Billed Curlews. The largest avian inhabitants of the wetlands – the egrets and herons – feed on a variety of large vertebrate and invertebrate prey. Rail species, known for their secretive nature, once used sanctuary marshes, but have declined dramatically. Grebes, coots and a host of diving ducks and dabbling ducks dominate the coastal bird assemblage that uses the shallow, tidal waters of local sloughs and estuaries.
On the outer coasts, the sandy beach avifauna is dominated by Sanderlings, Willets and Marbled Godwits. The dominant species on the rocky shoreline are the resident Black Oystercatchers and Black Turnstones. These birds are most abundant during fall and winter, and during this period they are accompanied by small numbers of Ruddy Turnstones, Surfbirds and Wandering Tattlers.
Shorebirds reach their greatest densities from October through March in Elkhorn Slough. This reflects the presence of individuals moving to and from northern breeding grounds as well as large numbers of over-wintering birds. However, many shore and marsh species occur year-round, including several that breed locally.
Sanctuary waters are important to several bird species of special concern because of their small populations:
- The Marbled Murrelet population in the sanctuary is the smallest, most disjunct and, therefore, most precarious breeding population of this species.
- The Western Snowy Plover, a threatened species, nests on beaches and is vulnerable to disturbance and trampling by humans. In addition, the red fox, an introduced predator, preys upon these small birds.
- Numbers of the endangered California Clapper Rail have severely declined, and the species may have been exterminated from marsh habitats in the sanctuary.
Human impacts to seabird populations include competition for food with commercial fisheries, entanglement in fishing gear, ingestion of marine debris, and disturbance of roosting and breeding birds by watercraft and aircraft.
In addition, environmental contamination from the historical use of pesticides still affects some species. For example, the almost total reproductive failure of the Caspian Tern colony in Elkhorn Slough in 1995 was likely due to the effects of pesticide-tainted sediments washing into the slough during torrential rains.
A number of smaller oil spills have injured and killed seabirds, including Common Murres, Marbled Murrelets and Rhinoceros Auklets, in the sanctuary. A large oil spill from tankers transiting sanctuary water is an ongoing threat to seabirds and shorebirds.
The variety and abundance of species found in the sanctuary provide a unique opportunity for observation. Monitoring seabirds and shorebirds can help detect critical population changes and provide essential data to determine what protection measures may be needed.
A number of ongoing multi-year studies are monitoring the distribution, abundance and movement patterns of large pelagic animals, including seabirds and marine mammals. West Coast CSCAPE, Tagging of Pacific Pelagic (TOPP), and Center for Integrated Marine Technology (CIMT) programs are three such monitoring programs. Highlights from other monitoring programs are described below.
Beach COMBERS (Coastal Ocean Mammal/Bird Education and Research Surveys)
In 1997, the sanctuary began this program using trained volunteers to survey beached marine birds and mammals monthly at selected beach sections from Waddell Creek to Morro Bay. The program’s long-term goals are to provide a baseline of the average presence of beach-cast marine organisms and to assist the sanctuary in early detection of die-offs or mortality events (which can be triggered by both natural and human-related environmental disturbances).
Data collected on the high deposition of Common Murres helped lead to the discovery of the threat gillnets pose to birds, harbor porpoises and sea otters. (For more information on Beach COMBERS, see the Beaches section.)
Tracking Black-Footed Albatross Movements and Conservation
The Black-Footed Albatross (Phoebastria nigripes) has recently been listed as endangered by the World Conservation Union (IUCN). Assessing albatross movements and habitats during the post-breeding season is a top conservation priority.
Eighteen birds were tagged in central California during the first two years of this study (2004-2005). Males and females were found to occupy different oceanic regions during the post-breeding season, with males venturing farther west than females. Overall, the tracked birds spent approximately 60 percent of their time in the high seas beyond national Exclusive Economic Zones. Of the time spend in U.S. territorial waters, 42 percent was spent within the three central California national marine sanctuaries.
The Distribution and Abundance of Marine Birds in Nearshore Waters of Monterey Bay
Monterey Bay is a site of regional significance for marine birds, particularly during winter. This study, completed by a researcher at Moss Landing Marine Laboratories, measured the seasonal abundance of nearshore (less than 1 kilometer, or 0.62 miles, from shore) marine birds and some of the factors affecting their distribution in Monterey Bay from 1999 to 2000.
Species assemblages were found to be fairly consistent between the same season in different years.
Total marine bird abundance was greatest during migration periods in spring and fall. Total marine bird diversity was greatest during winter. Mean density of all species (363 birds per square kilometer) was considerably greater than density reported for Monterey Bay as a whole, indicating that the nearshore environment should receive unique consideration in marine bird abundance and distribution studies.
Long-Term Studies of Seabirds on Año Nuevo Island and Mainland
Año Nuevo Island (ANI) is the largest and most diverse seabird breeding colony in the sanctuary, hosting breeding populations of seven species. In addition, the island is an important roosting site for Heermann’s Gulls and the endangered Brown Pelican.
Monitoring of seabirds on ANI by PRBO Conservation Science began in 1992. Rhinoceros Auklet, Brandt’s Cormorant and Western Gull populations increased from 2002 to 2003, to the highest levels yet recorded for the island. Auklet diet reveals a shift from an anchovy-based diet in the 1990s to a rockfish-based diet in recent years, corresponding to a shift in ocean climate in 1998-1999.
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