California Colonies 



Catalog Total 



2,690 birds 

 = colony sites 

 o = former sites 



Percent of California 

 Breeding Population. 



Breeding Chronology 



Northern California 



(20,21,29) 

 Clutch - 2-3 



Incubation Period - 30 days 

 Nestling Period - 13 wMkl 



Not Eroding 



ffumfcers in parentheses correspond co the 

 references from which ve obtained the data. 



B.rd Island 14540091 '. 



a l 



. . 



laying 



hatching 



17) 



No nesting attempts since 1966. Binding chronology 



from combined y*n 1933 to 1959. So* text. ? 7 



? 7 : 



Channel Islands 



egg laying 



(7,20) 



hatching 



adult* prasant 



Jan, | Feb. | Mar. | Apr. | May | June | July] Aug. I Sep. [ Oct. | Nov. | I 



pers. comm.). 



In the late 1960's and early 1970's, the 

 reproductive success of Brown Pelicans declined 

 considerably in California and northern Mexico. 

 From 1969 to 1971 only 12 chicks fledged out of 

 2,368 nesting attempts (Gress et al. 1973, 

 Anderson and Anderson 1976). The breeding 

 failures of Brown Pelicans during this period were 

 related to the high levels of DDE, the principal 

 metabolite of DDT, in the marine environment 

 (Schreiber and Delong 1969, Schreiber and 

 Riseborough 1972, Riseborough et al. 1971, Jehl 

 1973, Anderson and Anderson 1976). 



Brown Pelicans in California feed at the top 

 of a food chain that also includes plankton and 

 anchovies. At each higher level of this food 

 chain, concentrations of pesticides were magnified 

 until.- in Brown Pelicans, metabolism and depo- 

 sition of calcium in eggs were impaired and egg 

 shell thicknesses were reduced as much as 50 

 percent from normal (Anderson et al. 1975). 

 Breaking of thin-shelled eggs under the weight of 

 incubating adults reduced hatching success to 

 almost zero (Gress et al. 1973). Dumping of DDT 

 into the sewage system of the Los Angeles area 

 ceased in 1970 and since 1972 the reproductive 

 success of the Brown Pelican in southern California 

 and northern Mexico has improved. Ten years 

 after the DDT dumping ban, DDE levels have 

 stabilized at lower levels than in the past, but the 

 effects of this chemical on the Brown Pelican 

 continue. 



Brown Pelicans reach the northern limit of 

 their breeding range in southern California. 

 Historically, breeding populations of Brown 



Pelicans in southern California have fluctuated in 

 response to environmental conditions. Current 

 thought suggests that these populations increase 

 during periods of ocean warming (Baldridge 1973, 

 Anderson and Anderson 1976). The recent 

 history of this natural population flux has been 

 complicated since the 1950's by a consistent 

 decline in the numbers of Brown Pelicans because 

 of environmental contamination by chlorinated 

 hydrocarbons (Anderson and Anderson 1976). 



Although the threat of environmental 

 contamination by pesticides has diminished, the 

 future of the Brown Pelican in California is not 

 necessarily secure. Brown Pelicans can be seriously 

 affected by oil spills since they plunge dive to 

 feed and often sit on the water. They are limited 

 to nearshore areas where oil spills are likely to be 

 most common and severe. Brown Pelicans in 

 southern California feed almost exclusively on 

 Northern Anchovies, a fish also in great demand 

 by man. A sustained high commercial catch 

 could deplete the fish stocks necessary for success- 

 ful pelican nesting. Any changes in anchovy 

 management must take into account the require- 

 ments of a potentially expanding population of 

 Brown Pelicans. 



Breeding Brown Pelicans are highly suscep- 

 tible to disturbance. Reproductive success is 

 lower in colonies that have been disturbed by 

 man than in those undisturbed (Anderson and 

 Keith 1980). Increases in the number of tourists 

 at several colonies in Mexico could cause a serious 

 decrease in the reproductive success of this 

 species ,md might have important effects on 

 southern California populations. 



29 



