Biology and Ecological Niches in the Gulf of the Farallones 



Seabirds 



Peter Pyle 



Among the animals of the Gulf of the Faral- 

 lones, seabirds are the easiest to study. Resid- 

 ing above the water surface (for the most 

 part), seabirds are readily observed by land- 

 or boat-bound humans. They generally nest in 

 huge colonies on islands, facilitating research 

 on their breeding-population sizes and nest- 

 ing requirements. For these reasons, seabirds 

 are commonly used as barometers of the 

 health of marine ecosystems. This observa- 

 tion is true in the gulf, where a widely varying 

 marine environment supplies an interesting 

 extra dimension for study. 



"Seabirds" is not a technical term but 

 refers to individuals among a hodgepodge of 

 different bird families that share in common 

 their ability to make a living on the ocean. 

 In the Gulf of the Farallones there are 1 1 

 or 12 species of breeding seabirds, including 

 common murres, Cassin's and rhinoceros 

 auklets, western gulls, Brant's and pelagic 

 cormorants, storm petrels, pigeon guillemots, 

 and tufted puffins. Another 35 species of 

 migrant seabirds are regular visitors to the 

 gulf but do not breed there; examples of 

 these species include Pacific and red-throated 

 loons, red-necked and western grebes, black- 

 footed albatross, pink-footed, Buller's, and 

 black-vented shearwaters, herring and glau- 

 cous-winged gulls, and black and surf sco- 

 ters. About 25 additional species of non- 



breeding seabirds have been recorded rarely 

 or as vagrants in the gulf, including the 

 manx shearwater, an Atlantic species that has 

 recently been seen sporadically and could 

 even begin to breed in the gulf. 



All of the breeding species in the Gulf of 

 the Farallones nest on the Farallon Islands, 

 which are in the center of the gulf. Since 

 1968, biologists from the Point Reyes 

 Bird Observatory have monitored the size 

 and productivity of these populations. Only 

 through such long-term research can a full 

 understanding of the population dynamics 

 of these species and of their relation to the 

 marine environment be achieved. Some of 

 these species also nest on cliffs and small 

 islets along the Marin County coast, north of 

 the Golden Gate. 



The common murre typifies breeding sea- 

 birds in the Gulf of the Farallones. Before 

 the 1850's, an estimated 400,000 to 600,000 

 murres bred on Southeast Farallon Island, but 

 this population was decimated by egg collect- 

 ing in the wake of the California Gold Rush, 

 before chickens had arrived in sufficient num- 

 bers to provide eggs for the burgeoning San 

 Francisco populace. Other threats, such as 

 oilspills, human disturbance on the islands, 

 and the depletion of Pacific sardine stocks, 

 reduced populations further until they reached 

 a low of about 6,000 birds during the 1950's. 



Southeast Farallon Island became a National 

 Wildlife Refuge in 1969, and through pro- 

 tection and increased environmental aware- 

 ness, populations in the Gulf of the Farallones 

 gradually climbed to about 100,000 individu- 

 als by the year 2000. 



Common murres, along with the other 

 seabirds breeding at the Farallones, have 

 "good years" in which 90 percent or more of 

 the pairs successfully fledge a chick, and "bad 

 years" in which failure rates reach 50 percent 

 or more. These good and bad years generally 

 reflect the strength of the California Current, 

 the intensity of coastal upwelling, the pres- 

 ence and absence of "El Nino" events (see 

 chapter on Current Patterns Over the Conti- 

 nental Shelf and Slope), and the effects that 

 these processes have on juvenile rockfish, 

 anchovies, sardines, and other food resources. 



Because of the high levels of marine pro- 

 ductivity found in the Gulf of the Farallones, 

 many species that nest far away also come to 

 the region during their non-breeding seasons. 

 The most common of these species is the 

 sooty shearwater, which visit the Gulf of the 

 Farallones in late summer by the hundreds of 

 thousands, if not a million or more at a 

 time. Every autumn there is also a great 

 northward dispersal of organisms into the 

 Gulf of the Farallones from the south, follow- 

 ing the northward migration of the northern 



anchovy. Among the birds that follow this 

 migration are brown pelicans, Heermann's 

 gulls, and elegant terns. Many species of 

 loons, grebes, ducks, gulls, and alcids (a 

 family of diving seabirds having a stocky 

 body, short tail and wings, and webbed feet 

 they include the horned puffin, the ancient 

 murrelet, Xantu's murrelet, and the threat- 

 ened marbled murrelet) take up winter resi- 

 dence in the Gulf of the Farallones, escaping 

 the harsher winters of their Alaskan breeding 

 grounds. Finally, a few species of seabirds 

 breed to the north and winter primarily or 

 entirely to the south of the gulf. These long- 

 distance migrants, including phalaropes, jae- 

 gers, and Sabine's gull, can be seen passing 

 through the Gulf of the Farallones from July 

 to October and in April and May. 



Current threats to seabird populations in 

 the Gulf of the Farallones region include 

 effects of contaminants from San Francisco 

 Bay, overrishing, low-level or "chronic" oil 

 pollution, and mortality associated with gill- 

 netting in Monterey Bay. Declines in some 

 seabird populations in the gulf are occurring 

 because of these and other effects. Data on 

 the reproductive success and survival of these 

 seabirds, integrated with knowledge of food 

 resources and the marine environment, can be 

 used to assess the status and health of the 

 Gulf of the Farallones marine ecosystem. 



44 Biology and Ecological Niches in the Gulf of the Farallones 



