22 



Diets containing various levels of DDT (at 

 20 ppm, dry weight, or greater), or dieldrin (at 

 10 ppm, dry weight) caused significant reduc- 

 tion in eggshell thickness, weight, and cal- 

 cium in mallard ducks (Davison and Sell 

 1974). The reduction in eggshell thickness was 

 linear with increasing dose of dieldrin through 

 all levels studied. 



Mallards were fed untreated feed or feed 

 containing 40 ppm (dry weight) DDE, 40 ppm 

 PCB, or 40 ppm DDE + PCB beginning a 

 month before laying (Risebrough and Ander- 

 son 1975). Mean shell thickness indices were 

 similar in the control and PCB groups, but 

 they were reduced by 17% in the DDE group 

 and 19% in the DDE + PCB group. The con- 

 tents of 12 eggs randomly selected from the 

 DDE group contained 373 ppm DDE (lipid 

 basis), and 13 eggs from the DDE + PCB 

 group contained mean residues of 344 ppm 

 DDE + 364 ppm PCB (lipid basis). Egg pro- 

 duction was similar in all groups for about the 

 first 7 weeks, then it dropped markedly in the 

 DDE -I- PCB group. Part, but not all, of this 

 group's lower production of intact eggs was 

 caused by egg eating. This behavior ac- 

 counted for 18 of 282 eggs observed lost in 

 the DDE + PCB group, 6 of 394 eggs in the 

 PCB group, and none in the control and DDE 

 groups. Although there was no significant 

 change in shell thinning or DDE residues 

 when PCB was added to the diet, the reduc- 

 tion in the number of intact eggs produced by 

 the DDE -I- PCB group suggests that the two 

 compounds may nevertheless interact to in- 

 fluence reproductive success. 



Behavior 



In England, gray herons (Ardea cinerea) 

 have been observed breaking their own eggs, 

 and others dropped their live young from the 

 nest (Milstein et al. 1970; Prestt 1970). Such 

 aberrant behavior may be related to sublethal 

 organochlorine residues in the birds, as these 

 authors suggested. The birds did not eat the 

 eggshells, but tossed even the fragments from 

 the nest. Therefore, the alternative possibility 

 of calcium "hunger" does not seem to be true 

 in herons. 



Mallard ducks fed a diet containing 3 ppm 

 DDE (dry weight; equal to about 0.6 ppm in a 

 natural succulent diet) laid eggs that con- 

 tained an average of 5.8 ppm DDE; ducklings 



that hatched from these eggs differed from 

 controls in behavioral tests designed to 

 measure responses to a maternal call and to a 

 frightening stimulus (Heinz 1976b). In re- 

 sponse to the maternal call, ducklings from 

 parents fed DDE were hyper-responsive; com- 

 pared with controls, a greater percentage ap- 

 proached the call and a greater percentage of 

 those that approached remained near" the call 

 for the remainder of the test. In a test of 

 avoidance behavior, ducklings whose parents 

 were fed DDE traveled shorter distances from 

 the frightening stimulus than did controls. 



Coturnix quail chicks were given sublethal 

 amounts of chlordane, dieldrin, endrin, DDE, 

 or Aroclor 1254 in their feed, beginning at 

 7 days of age, and their avoidance response to 

 a moving silhouette was measured daily for 

 14 days (Kreitzer and Heinz 1974). The birds 

 were on dosage for 8 days, and on untreated 

 feed for 6 days immediately thereafter. Group 

 avoidance response was significantly sup- 

 pressed (P from 0.01 to < 0.001) by chlordane, 

 dieldrin, endrin, and Aroclor 1254, but no 

 effect of DDE on the birds' behavior could be 

 detected. The behavior of the endrin-treated 

 birds returned to normal after 2 days on un- 

 treated feed. The data indicated partial recov- 

 ery for birds treated with dieldrin and chlor- 

 dane, but none for those treated with Aroclor 

 1254. 



Heavy Metals 



The sources, occurrence, food web transfer, 

 and toxicology of heavy metals and other 

 trace elements must be understood to eval- 

 uate the significance of these chemicals to ma- 

 rine birds. These more general aspects have 

 received considerable attention in recent sym- 

 posia and reviews (Larsson 1970; Nelson et al. 

 1971; Gavis and Ferguson 1972; Eisler 1973; 

 National Research Council of Canada 1974; 

 Leland et al. 1975). Consequently, our discus- 

 sion will be restricted to the more specific 

 aspects of the exposure of aquatic birds to 

 these chemicals, but will include some inter- 

 pretive information relative to terrestrial 

 avian species. 



Most techniques that are used for measur- 

 ing mercury residues in environmental 

 samples determine levels of total mercury, re- 

 gardless of the chemical form in which it 



