nest throughout incubation. Desertion of the nest 

 can resuh in losses to predation as well as tem- 

 perature stresses on the eggs and young (Schreiber 

 and Risebrough 1972, Schreiber 1979). 



Mercury may also interfere with reproduction; 

 mercury has been found in some pelican eggs at 

 levels known to have adverse effects on other spe- 

 cies (Blus et al. 1974a). 



Eastern subspecies 



Along the Atlantic Coast, eggshell thinning is 

 more acute at the northern end of the pelican's 

 range (Blus et al. 1970). From 1969 to 1974, Blus 

 et al. (1974a) noted that 17% eggshell thinning in 

 North Carohna populations was associated with 

 subnormal reproductive success. By 1975, egg- 

 shell thinning had decreased to 10% (L. J. Blus 

 personal communication). The present Florida 

 population is stable, eggshell thickness has been 

 reduced about 9%, and about 3% of all eggs on 

 the west coast of Florida have been thin-shelled 

 and crushed. The effects of these factors on pop- 

 ulation levels may not be apparent, for in 1975 

 and 1976, eggs in Florida had little or no thinning 

 or crushing (R. W. Schreiber personal communica- 

 tion). 



In Louisiana and Texas, where the pelican 

 populations have declined rapidly and dramat- 

 ically, the levels of pollution are higher (Schrei- 

 ber and Risebrough 1972). In Louisiana, eggs 

 from transplanted Florida birds showed a steady 

 decline in shell thickness from 1970 to 1973. 

 Levels of DDE were generally lower than those 

 associated with subnormal reproductive success 

 in South Carolina, but dieldrin levels were slightly 

 higher. Half the eggs examined contained levels of 

 dieldrin considered potentially detrimental to re- 

 productive success (Blus et al. 1975). 



Forty percent of a small population trans- 

 planted to Louisiana from Florida died of endrin 

 poisoning in the spring and summer of 1975 

 (Winn 1975). 



Freezes, hurricanes, and beach erosion may 

 have affected population numbers (Schreiber and 

 Risebrough 1972). Blus et al. (1974a) believe that 

 in South Carolina, storms and other naturad fac- 

 tors have minimal effects on pelican populations 

 because, while they may temporarily disrupt nest- 

 ing activities, the birds are persistent renesters in 

 that area. 



Human disturbance that causes the parent 

 birds to desert the nests can result in serious losses 

 to predation by fish crows (Corvus ossifragus), as 

 well as in temperature stress on eggs and young 



(Schreiber and Risebrough 1972, Schreiber 1979). 



In Florida, a significant number of pelicans 

 (500 or more) are killed each year after being 

 caught on fishhooks or entangled in monofila- 

 ment fishlines. Some are also maliciously killed or 

 maimed by people (Schreiber 1979). 



The decline of the pelicans in South Carolina 

 in the 1950's coincided with a decline in Atlantic 

 menhaden [Brevoortia spp.). There is some evi- 

 dence that food shortages occur, especially in 

 Florida, and the red tide (Gymnodimium) has 

 probably affected pelican food supplies on the 

 west coast of Florida at times (Williams et al. 

 1976). 



California subspecies 



Pelican losses in California resulting from 

 paratyphoid infections have probably had little 

 effect on the total population (Bond 1942). The 

 complete failure of reproductive efforts on the 

 California Channel Islands in 1968, reported by 

 Schreiber and DeLong (1969), probably resulted 

 from chlorinated-hydrocarbon pollution. Levels 

 of residues as high as 84.4 ppm were found in the 

 muscles of birds from Monterey Bay in December 

 of 1966 (Risebrough et al. 1971). Reproduction 

 on Anacapa Island, California, and Los Coronados 

 and San Martin Islands in Baja California, was al- 

 most entirely unsuccessful from 1969 to 1972. 

 Success varied on San Benito Island in Baja Cali- 

 fornia (400 miles south of the U.S. border) and 

 on remote islands in the Gulf of California. Far- 

 ther south, reproductive success Wcis more satis- 

 factory. The U.S. Fish and Wildhfe Service (1973) 

 attributed the poor reproductive success to egg- 

 shell thinning brought about by contamination 

 with DDE. 



In 1974, eggshell thinning was much less evi- 

 dent than in previous years on the Pacific Coast, 

 and many more young were produced in some of 

 the colonies where egg collapse had been severe. 

 More adults bred in 1974, as well. However, col- 

 lapsed eggs and lowered productivity continued 

 to be evident. Production on San Martin Island 

 failed completely in 1974, presumably because 

 of human disturbance. 



In the Gulf of California, where production 

 had been comparatively good, it was very poor in 

 1974. The cause appeared to be poor food condi- 

 tions, although the presence of DDE in the food 

 chain may have contributed. A decrease in the 

 availability of anchovies brought about by over- 

 fishing is thought to have affected brown pelican 

 reproduction (Keith 1978). Recent studies indi- 



