(Fulmarus glacialis) and gulls. This new food 

 supply may be in part responsible for increases in 

 fulmar and gull numbers in some parts of the 

 world (Brown 1970, Bourne 1972). Commerical 

 fishing in California is primarily from small, 

 privately-owned boats and offal discharge is 

 probably insignificant at present. Coastal garbage 

 dumps are likely a more important food source 

 for gulls. 



Commerical fisheries are increasingly harvest- 

 ing species of fish used by seabirds for food. This 

 is due largely to an increasing demand for fish 

 products, depletion of more desirable species, and 

 improved fishing technology. Fish stocks can 

 become so depleted through overfishing that 

 decreases in populations of seabirds can result. 

 This is best illustrated by the crash of Peruvian 

 seabird populations following overfishing of the 

 anchoveta (Engraulis ringens). In the years 

 between 1953 and 1965, Peruvian seabird popula- 

 tions declined from 28 million birds to 4 million 

 birds (Schaefer 1970). 



A similar conflict seems likely to occur 

 between the Northern Anchovy (Engraulis 

 mordax) and seabird populations along the west 

 coast of Mexico and southern California. The 

 diet of breeding Brown Pelicans in southern 

 California has been found to contain 92 percent 

 anchovies (Gress pers. comm.). Brown Pelicans 

 reproduce best during periods when anchovies are 

 abundant near breeding colonies (Anderson et al. 

 1980). Although pre-1979 harvest levels of 

 anchovies probably did not affect Brown Pelican 

 reproduction, potential increases in the harvest 

 proposed under some options of the Anchovy 

 Management Plan, Pacific Fisheries Management 

 Council, could be serious (Anderson et al. 1980). 

 Hunt and Butler (1980) have shown the im- 

 portance of anchovies to the reproductive success 

 of Xantus' Murrelets and Western Gulls on Santa 

 Barbara Island (524 008, See page 56). 



Protecting seabird feeding areas, particularly 

 those near breeding colonies, may be necessary. 

 Caution should be used before any decision to 

 increase anchovy harvests is made (MacCall 1974, 

 Radovich 1979, Anderson et al. 1980). Little 

 information is available on the effects of fisheries- 

 caused depletion of prey species on other 

 California seabirds and continued research is 

 needed (Anderson et al. 1980). 



HUMAN DISTURBANCE 



A serious danger to nesting seabirds is 

 disturbance by people, including scientists, bird- 



watchers, recreationalists, and others. Disturbance 

 is usually unintentional and, more often than not, 

 the culprits are unaware of the harm that they 

 have caused. When people go into or near a 

 seabird colony they can cause disturbance in 

 many ways. An awareness of potential problems 

 can do much to reduce disturbance. 



Flushing birds from nests must be avoided 

 since it can cause adults to abandon nests, exposes 

 eggs and chicks to predators, and interferes with 

 incubation and the feeding of chicks. During 

 panic departures adults may even break eggs or 

 kick eggs and chicks from nests. Larger chicks 

 may run off and, unable to get back to the nest, 

 may die or be killed. Airplanes, boats, and 

 helicopters, as well as individuals on foot, can 

 cause birds to flush by approaching a colony too 

 closely. Helicopters are especially disruptive. 



In California, predation on uncovered eggs 

 and chicks is primarily by Western Gulls and 

 Common Ravens (Corvus corax). Both gulls and 

 ravens patrol colonies in search of unattended 

 eggs and chicks or for a chance to steal food 

 brought in by parent birds. Under natural circum- 

 stances their success rate is low, but a colony from 

 which adults have been flushed is "easy pickings." 

 Plundering gulls may walk ahead of human 

 intruders, pecking holes into eggs, or they may fly 

 off with eggs to eat elsewhere (Anderson and Keith 

 1980). Gulls calling overhead attract more gulls 

 and add to the panic of the colony (Anderson and 

 Keith 1980). Western Gulls are formidable 

 predators. They will consume young chicks 

 whole, including chicks of their own species, and 

 will even attack large 3 to 4 week old pelican 

 chicks to obtain regurgitations or will remove the 

 eyes, uropygial glands, and entrails, causing death 

 (Anderson and Keith 1980). 



Incubation of eggs and chicks is a means of 

 maintaining an optimum temperature for rapid 

 development. Parents sit on and turn eggs to 

 warm them and will shade eggs and chicks from 

 the sun to keep them from overheating. If parent 

 birds are kept off their nests for a long enough 

 period of time, death of the young from hyper- 

 thermia (overheating) or hypothermia (over- 

 cooling) can occur. Shorter periods of neglect 

 can extend the incubating time required for 

 hatching. 



The most damaging type of human distur- 

 bance is physical alteration of habitat, since its 

 effects are longterm, and in most cases irreversible. 

 Whaler Island (325 045) near the Oregon border 

 is now part of the Crescent City breakwater and is 

 no longer used by nesting seabirds. Osborne 



