grown young were still present (Bond 1942). 



Adult pelicans usually stayed on nests until 

 approached within 5 or 6 m and returned by the 

 time that observers were about 30 m away, but 

 even so, ravens carried off at least 8 eggs when 

 they were left exposed (Bond 1942). 



On 20 March 1969, R. W. Risebrough (Report 

 to Patuxent Wildlife Research Center, 24 April 

 1969) counted 298 nests containing fresh plant 

 material, indicating occupancy, on Anacapa Is- 

 lands, but only 12 contained intact eggs. Nine 

 contained a single egg and 3 contained 2 eggs. 

 Fifty-one nests contained a single broken egg. 

 Eggshells were spongy in texture and slight pres- 

 sure produced a change in shape. Shells appeared 

 to have very little or no calcium carbonate, and it 

 was apparent that the weight of incubating birds 

 would cause breakage. One of the broken eggs 

 had a DDE content of 68 ppm of the total con- 

 tents or 522 ppm of yolk lipid. In a second colony 

 on Anacapa on April 1969, there were 339 nests, 

 with only 19 containing intact eggs and 1 out of 

 3 nests having collapsed, dehydrated eggs (Monthly 

 Report, Denver Wildlife Research Center April 

 1969). On 26 and 27 July 1969, 635 nests were 

 found on Anacapa. Two nests contained large 

 chicks and 2 contained single incubated eggs. 

 Thus, out of a minimum of 1272 nests built in 

 1969, only 5 may have produced young (F. H. 

 Sibley, Report to Patuxent Wildhfe Research Cen- 

 ter, 28 July 1969). 



There were 552 nesting attempts in two 

 colonies on Anacapa in 1970, with but one chick 

 produced. Reproductive failure was attributed to 

 thin eggshells that collapsed during incubation. 

 Aberrant behavior associated with reproduction 

 was also observed. A survey of all traditional nest- 

 ing sites in California produced no evidence of 

 nesting. To the best of our knowledge, then, only 

 one young pelican was hatched in California in 

 1970 (Cress 1970). 



A total of 1,962 eggshells taken after 1949 

 for California oological collections were 26% be- 

 low the normal weight of egg specimens taken 

 before 1949, supporting the belief that shell thin- 

 ning began after the wide-scale use of pesticides 

 (Anderson and Hickey 1970). 



By use of stepwise regression, Blus et al. 

 (1971) found that DDE was the only residue that 

 accounted for a significant amount of pelican egg- 

 shell thinning; accounted for a significant amount 

 of pelican eggshell thinning; PCB's appeared to be 

 of Uttle, if any, importance in this respect. 



On Border Island, Los Coronados, Baja Cali- 

 fornia, only 19 intact eggs were found in 300 

 nests in April 1969. On Martin Island, 150 miles 



south of the U.S. border, only 17 eggs were found 

 in 100 nests (Monthly Report of Denver Wildlife 

 Research Center, April 1969). 



Brown pelicans showed varying reproductive 

 success in different parts of their range and from 



1969 to 1971, with the poorest off the California 

 coast, improving slightly down the west coast of 

 Baja California, and the best in the Gulf of Cali- 

 fornia. About 4.4% of the population is suffering 

 widespread excessively low recruitment. Of the 

 relatively satisfactory Gulf of California popula- 

 tion, it is estimated that 20% suffered eggshell 

 thinning in excess of 1 l%o. Anacapa Islands, Los 

 Coronados, and west coast Baja Cahfornia pop- 

 ulations had the most eggshell thinning in 1968, 



1970 and 1971. Here again, DDE seems to be the 

 major factor contributing to thin eggshells and re- 

 sults in some reduction in reproduction. Other 

 factors reducing reproduction related to human 

 interference of several types. Various data suggest 

 that the major source of DDE for brown pehcans 

 is off Southern California (Anderson et al. 1975). 



An indication of improved production on the 

 California Islands was noted in 1972, when 112 

 nests were counted on Scorpion Rock off Santa 

 Cruz Island, and 31 young had been produced 

 there by 13 July. In the same year, 150 nests 

 from which 26 young had been produced were 

 found on Anacapa. Early nest failures were evi- 

 dent from the many cracked eggshells (from 

 Monthly Narrative Report of Activities of Denver 

 Wildlife Research Center, August 1972 by David 

 W. Anderson and L. Rodney DeWeese). 



In 1974, eggshell thinning was much less evi- 

 dent on the Pacific coast; many more young were 

 produced and more adults bred in some colonies. 

 About 1,400 adult pelicans were present in July 

 on Anacapa and Santa Cruz Islands, where they 

 build about 400 nests and produced about 300 

 young. However, collapsed eggs were found and 

 30% of nests on the islands were empty and de- 

 serted. Also, 15% of the adults were incubating 

 addled eggs. About 0.75 young per nest were pro- 

 duced, which is still too little; about 1.3 to 1.5 

 young per adult pair are required to maintain the 

 population. On the Coronados Islands, Baja Cali- 

 fornia, the colony was much larger in 1974 than in 

 any recent year but productivity averaged only 

 0.70 young per nest and collapsed eggs and nest 

 desertions were common (up to 30% in some 

 areas). On Isla San Martin, pelicans built 112 

 nests, all of which failed, probably due to human 

 disturbance. At Isla San Benito, production was 



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