INTRODUCTION 



This catalog is a summary of the location, 

 size, and species composition of seabird colonies 

 along the California coast. It documents more 

 than 260 nesting areas with a total estimated 

 population of nearly 700,000 birds. 



Our study was sponsored by the Bureau of 

 Land Management, Pacific Outer Continental 

 Shelf Office, to fulfill requirements of the Nation- 

 al Environmental Policy Act of 1970. The 

 information will help resource planners evaluate 

 possible effects on seabirds of proposed oil and 

 gas leasing. Detailed information on seabird 

 distribution and abundance will be useful to 

 coastal planners, scientists, and amateur bird- 

 watchers. For this reason, we have included a 

 section on threats to seabirds and appendices on 

 the archiving of our field data (Appendix A) and 

 viewpoints from which several colonies can be 

 observed without causing disturbance (Appendix 

 B). 



Seventeen species of seabirds from six 

 families are discussed in this report. These 

 include four species of storm-petrels (Fork -tailed, 

 Leach's, Ashy, and Black), one species of pelican 

 (Brown Pelican), three species of cormorants 

 (Brandt's, Double-crested, and Pelagic), one 

 species of shorebird (Black Oystercatcher), one 

 species of gull (Western Gull), and seven species 

 of alcids (Common Murre, Pigeon Guillemot, 

 Marbled Murrelet, Xantus' Murrelet, Cassin's 

 Auklet, Rhinoceros Auklet, and Tufted Puffin). 

 In addition to population information in the 

 maps and tables, species accounts discuss aspects 

 of the natural history of each of the above 

 species, emphasizing the California populations. 



Population information for six additional 

 species which could also be affected by coastal 

 development and pollution has been included in 

 the maps and tables. All the known locations of 

 Least Tern (Sterna albifrons) colonies are iden- 

 tified in this catalog, although yearly surveys by 

 the California Department of Fish and Game will 

 soon render this data obsolete. The catalog also 

 identifies coastal breeding sites of the Caspian 

 Tern, (Sterna caspia), Forster's Tern (Sterna 

 forsteri), and Black Skimmer (Rynchops niger), 

 species which also breed inland. The single 

 known California nesting location of the Elegant 

 Tern (Sterna elegans) in San Diego Bay is also 

 identified. Finally, locations of known Heer- 

 mann's Gull (Lams heermanni) nest sites are 



indicated, although this species was never re- 

 corded breeding in California until 1980, and 

 cannot be considered part of the normal breeding 

 avifauna. All six species, except Heermann's 

 Gulls and some Least Terns, nest and feed pri- 

 marily in enclosed bays and estuaries. Our 

 inclusion of this information is intended only to 

 supplement other sources of information on these 

 species. 



It must be recognized that this report only 

 documents nesting sites. Large numbers of 

 non-nesting birds migrate through coastal 

 California in spring and fall and many additional 

 birds winter along the coast. These include shear- 

 waters from as far away as New Zealand and 

 Tasmania, many kinds of shorebirds and waterfowl 

 from arctic Alaska and Canada, pelicans and gulls 

 from Mexico, and inland nesting birds such as 

 grebes and small gulls. Oil spills and other dis- 

 turbances could severely affect these populations. 

 Seabirds are truly an international resource and 

 must be managed as such. 



THE NATURE OF SEABIRDS 



Seabirds evolved in an environment free of 

 most of the competition and predators faced by 

 terrestrial birds. They have evolved into birds 

 with long lifespans, low adult mortality rates, 

 relatively late sexual maturity, and small clutch 

 sizes. Lifespans of seabirds are not exactly 

 known, but they are certainty long in comparison 

 to most terrestrial birds. Records exist of indivi- 

 duals of several species of seabirds reaching more 

 than 20 and even 30 years of age (Bergstrom 

 1952, Clapp and Sibley 1966, Clapp and Hack- 

 man 1968, Graham 1980). Long lifespans in a 

 species imply a low annual rate of adult mor- 

 tality, and annual mortality rates below 20 

 percent are common in seabirds (Ashmole 1971, 

 Richdale and Warham 1973). Some albatrosses 

 may have annual mortality rates as low as three 

 percent (Lack 1954). Many passerines, at the 

 other extreme, have annual mortality rates from 

 40 to 70 percent (Lack 1954). If mortality rate 

 remains constant with increasing age, large 

 seabirds with very low annual mortality rates may 

 attain a breeding life of 50 years or more (Ashmole 

 1971). In addition, recruitment of birds into the 

 breeding population is often slow and delayed. 

 Before attaining maturity, many seabirds spend at 

 least 2 years, and more commonly 3, 4, 5, and up 

 to 9 years as non-breeders (Ashmole 1971). Long 



