breeding lives, low recruitment rates, and delayed 

 maturity could delay the effects of successive 

 breeding failures on breeding populations for 

 several years. 



The clutch size of seabirds is usually low. 

 Storm-petrels and other procellariiformes lay one 

 egg, alcids lay one or two eggs, and pelicans and 

 gulls lay one to three eggs. Cormorants may lay 

 up to seven eggs, though clutches of four or five 

 are more common. By contrast, many land birds 

 lay from 7 to 15 eggs and many produce two 

 broods each year. 



Because seabirds reproduce at a slow rate 

 but over a long lifetime, the effects of an oil spill 

 or other disaster and the potentially more danger- 

 ous effects of longterm chronic pollution, habitat 

 loss, and other disturbances demand careful and 

 frequent monitoring of seabird populations. 



Seabirds tend to be of two types: those 

 which spend most of their time near shore (in- 

 cluding cormorants, pelicans, and most gulls), and 

 those which come to land only during the breeding 

 season or sometimes intermittently during other 

 times of the year (including storm-petrels and 

 alcids). Of the truly pelagic seabirds, several are 

 nocturnal on the breeding grounds; they will 

 enter or leave their colonies only at night. In 

 California, the four storm-petrels, Marbled and 

 Xantus' Murrelets, Cassin's Auklets, and, to a 

 lesser degree, Rhinoceros Auklets are nocturnal on 

 their breeding grounds. 



The seabird colony is the most critical 

 habitat for seabirds because reproduction and 

 thus continuation of species depend on these 

 sites. Here the population will reach its annual 

 low, just before young are hatched, and its annual 

 high, just after hatching. At other times of the 

 year, seabirds may be able to avoid problems such 

 as disruption of food supplies, and perhaps even 

 large oil spills, simply by flying somewhere else, 

 but for successful nesting they are limited to the 

 area around the colony. 



In the following section, we discuss some of 

 the problems which face seabirds. We hope an 

 awareness of these will alert coastal planners to 

 the kinds of problems that may be encountered. 



THREATS TO SEABIRDS 



OIL 



leasing program by the Bureau of Land Manage- 

 ment offshore of California was initiated in 1963. 

 Areas in the Santa Barbara Channel were leased in 

 1 966 and 1 968 , and other sections of the Southern 

 California Bight were leased in 1975. Five new 

 oil lease zones were identified offshore of central 

 and northern California in 1977. The southern- 

 most of these tracts is scheduled for sale in 1981. 



Resource planners must be aware of potential 

 hazards to seabirds that may be caused by oil 

 development. There is ample literature document- 

 ing the lethal effects of oil on marine birds, 

 including papers by Bourne (1968, 1970), Clark 

 (1969), Clark and Kennedy (1968), Croxall 

 (1975), Manuwal (1978), and many others. 

 Vermeer and Vermeer (1974) reviewed the 

 literature appearing between 1922 and 1973 on 

 the effects of oil on birds. 



One effect of oil on seabirds is destruction 

 of the insulating properties of feathers. An oiled 

 bird compensates for the loss of insulation and 

 subsequent loss of heat by increasing its metabolic 

 rate, using stored energy (Hartung 1967). If 

 the bird's energy balance is not restored, energy 

 reserves are soon depleted and death from hypo- 

 thermia results. Oiled birds are unable to maintain 

 their energy reserves because they cannot or will 

 not feed. 



Marine birds may also ingest oil while 

 drinking, feeding, and especially when oiled 

 individuals attempt to preen their soiled plumage. 

 Ingestion of oil may hinder the absorbtion of 



Oil exploration, production, and transport 

 are important industries along the coast of 

 California. A federal outer continental shelf 



A Common Murre fouled with oil on a Pacific 

 Coast beach. Photo by Duncan McDonald 



