20 



crease in DDD was greatest. In 1973, the peli- 

 cans experienced excellent reproductive 

 success for the first time in many years, and 

 the decline in residues was related to this im- 

 provement. DDE was implicated as the agent 

 responsible for most pollutant-induced nest 

 failure; residues above 3.7 ppm in the sample 

 egg were associated with total failure of those 

 eggs remaining in the nest. The improvement 

 in reproductive success was not associated 

 with an increase in average eggshell thick- 

 ness. 



The peregrine falcon appears to be affected 

 by shell thinning in all areas of its nearly glo- 

 bal range thus far examined, including areas 

 in the Aleutians (Peakall et al. 1975), Green- 

 land (Walker et al. 1973), and coastal Chile 

 (Walker et al. 1973) where they depend on ma- 

 rine food chains. On the Auckland Island in 

 the sub- Antarctic, one egg of the New Zealand 

 falcon contained DDE residues that were 

 similar to those associated with shell thinning 

 in the closely related peregrine (Bennington et 

 al. 1975). 



Peregrine falcons that breed along the coast 

 of Scotland feed largely on seabirds, and these 

 populations have declined in numbers at a 

 time when populations that were preying on 

 land birds in the interior remained stable (Rat- 

 cliffe 1972). A decline in reproductive success 

 of the white-tailed eagle (Haliaeetus albicilla) 

 in Germany has most likely been caused by 

 DDE (Koeman et al. 1972b). In the Baltic, 

 where white-tailed eagle populations declined 

 during this century (Henriksson et al. 1966), 

 very high concentrations of PCB and DDT 

 compounds have been measured in eagles that 

 were found dead (Jensen et al. 1972). 



During an early study, the population of the 

 Bermuda petrels (Pterodroma cahow) was 

 undergoing an unexplained decline that was 

 attributed to the presence of DDT (Wurster 

 and Wingate 1968), but reproductive success 

 subsequently improved. Reexamination of the 

 tissues that had been analyzed for DDT, and 

 analysis of dead chicks and unhatched eggs 

 obtained subsequently, showed no changes in 

 either DDT or PCB concentrations during the 

 periods of poor reproductive success and sub- 

 sequent recovery. Moreover, residues were 

 comparatively low when related to those of 

 other species of petrels in more contaminated 

 areas (D. Wingate and R. W. Risebrough, un- 

 published data). 



Shell thinning of eggs of the osprey in the 

 northeastern United States where reproduc- 

 tion has been low and where population 

 numbers have declined is also related to DDE 

 concentrations (Spitzer et al. 1977). Dieldrin 

 and PCB's also may have contributed to the 

 rapid population decline in the affected areas 

 in the Northeast, principally Connecticut 

 (Wiemeyer et al. 1975). 



In the Northeast, shell thinning has been 

 documented in eggs of the gannets breeding 

 on Bonaventure Island (J. A. Keith, personal 

 communication). The breeding population of 

 gannets, after increasing over the previous 

 80 years, declined by 16% between 1969 and 

 1973 (Nettleship 1975). In the recent past, 

 DDT was extensively used in forest spray op- 

 erations in adjacent areas of New Brunswick. 



Patterns of reproductive failure in declining 

 populations of several European and North 

 American raptorial species were duplicated 

 experimentally with captive American kes- 

 trels that were given a diet containing dieldrin 

 and DDT, two commonly used organochlorine 

 insecticides (Porter and Wiemeyer 1969). 

 Major effects on reproduction were increased 

 egg disappearance, increased egg destruction 

 by parent birds, and reduced eggshell 

 thickness. 



In other experimental studies, DDE has 

 caused significant eggshell thinning in cap- 

 tive screech owls (Otus asio) (McLane and 

 Hall 1972) and American kestrels (Wiemeyer 

 and Porter 1970). The levels of DDE found in 

 the kestrel eggs in the second reproductive 

 season of that study are similar to those 

 found in British peregrine falcon eggs (Rat- 

 cliffe 1967). 



Bald eagle eggs collected in 1968 from nests 

 in Wisconsin, Maine, and Florida all con- 

 tained residues of DDE, DDD, dieldrin, hep- 

 tachlor epoxide, and PCB's (Krantz et al. 

 1970). Many also contained traces of DDT. 

 Eggs from five nonproductive nests in Maine 

 contained much higher residues than did eggs 

 collected from either productive or nonpro- 

 ductive nests in Wisconsin and Florida. 



Twenty-three bald eagle eggs collected in 

 Alaska, Maine, Michigan, Minnesota, and 

 Florida during 1969 and 1970 were analyzed 

 for organochlorines and mercury (Wiemeyer 

 et al. 1972). All eggs contained residues of 

 DDE, dieldrin, PCB's, and mercury. Average 

 residue concentrations were lowest in eggs 



