28 



decline in this species in Finland also was as- 

 sociated with mercury contamination (Hen- 

 riksson et al. 1966). However, as discussed 

 earlier, organochlorines also may be partially 

 responsible for the observed decline. 



There were apparently no young produced 

 by common loons in Clay and Ball Lakes, On- 

 tario, in 1970 and 1971 (Fimreite 1974). (Both 

 lakes receive effluent from a chlorine plant.) 

 Fledging success of common terns at Ball 

 Lake was 10% of normal, but fledging was 

 normal at nearby Wabigoon Lake, where 

 birds contained lower residues. Average total 

 mercury in the eggs was 3.6 and 1.0 ppm; 

 average methyl mercury was 2.4 and 0.8 ppm 

 in the two colonies. 



There are considerable differences between 

 species in susceptibility to mercury pollu- 

 tants. Mercury concentrations as high as 

 16 ppm in western Ontario herring gull eggs 

 apparently did not affect their hatchability 

 (Vermeer et al. 1973), but 0.5 to 1.5 ppm mer- 

 cury in ring-necked pheasant eggs reduced 

 hatchability, reduced egg weight and produc- 

 tion, and produced a large number of eggs 

 without shells (Fimreite 1971). 



Concentrations of mercury found in the 

 livers of abnormal young terns (Sterna 

 hirundo and S. dougallii) from Great Gull 

 Island (in Long Island Sound) ranged from 

 0.2 to 1.2 ppm, but were not thought to have 

 caused the abnormalities (Hays and Rise- 

 brough 1972). Livers of normal young terns 

 were not analyzed. Hatchability in the Great 

 Gull Island colony has consistently been 

 greater than 90%, but hatchability of com- 

 mon tern eggs in Lake Ontario colonies has 

 been low. Concentrations of heavy metals in 

 common terns were studied to determine the 

 reason for the difference in hatchability. Con- 

 centrations of cadmium, chromium, cobalt, 

 copper, lead, mercury, nickel, silver, and zinc 

 in bone, liver, breast muscle, and kidneys of 

 adult birds from the two locations were simi- 

 lar (Conners et al. 1975). Therefore, these 

 metals apparently were not responsible for 

 the differences in hatchability. 



Although the reproductive effects of mer- 

 cury in other species are largely unknown, 

 mercury residues of 0.5 ppm were associated 

 with poor reproductive success in an experi- 

 mental study with ring-necked pheasants 

 (Fimreite 1971). Average mercury residues in 

 field-collected eggs of four species of aquatic- 

 related birds on the Niagara peninsula, On- 



tario, were between 0.5 and 1 ppm (Frank et 

 al. 1975). These included red-winged blackbird 

 (Agelaius phoeniceus; 0.68 ppm), herring gull 

 (0.74 ppm), black-crowned night heron 

 (0.64 ppm), and common tern (0.83 ppm). 



Mercury was found in measurable quanti- 

 ties in all of the 100 brown pelican eggs from 

 13 colonies in South Carolina, Florida, and 

 California (Blus et al. 1974a). Six of the 21 

 pelican eggs from South Carolina contained 

 0.5 ppm or more of mercury. Sixteen of the 49 

 pelican eggs from Florida contained 0.5 ppm 

 or more of mercury, and 1 on the verge of 

 hatching contained 1.43 ppm. 



Methyl mercury at low dietary levels (0.5 or 

 3.0 ppm, dry weight, equal to about 0.1 or 

 0.6 ppm mercury on the basis of a natural suc- 

 culent diet) caused lowered reproductive 

 success in experimental mallards and black 

 ducks. Mallards fed 3 ppm mercury in their 

 diet during one reproductive season showed 

 reproductive impairment, but none was 

 evident among birds fed 0.5 ppm (Heinz 

 1974). Adverse effects in the group fed 3 ppm 

 included a decrease in egg laying, an increase 

 in embryonic mortality, and reduced duckling 

 survival. These effects resulted in the produc- 

 tion of less than half (46.5%) as many 1-week- 

 old ducklings as the controls. Levels of mer- 

 cury reached about 1 ppm in eggs of the birds 

 fed 0.5 ppm mercury and between 6 and 

 9 ppm in the eggs from ducks fed 3 ppm 

 mercury. 



The hens from the first reproductive season 

 were kept on diets containing mercury into a 

 second season (Heinz 1976a). During the sec- 

 ond season, levels of mercury in eggs from 

 hens on these diets averaged 0.79 and 

 5.46 ppm. On a dry-weight basis, the concen- 

 tration of mercury in eggs was about 5 times 

 that in the feed. There were no significant dif- 

 ferences in egg production or hatching suc- 

 cess among control birds and those fed mer- 

 cury. However, duckling survival decreased: 

 ducklings from hens fed 3 ppm mercury 

 during the two reproductive seasons were less 

 likely to survive to 1 week of age than were 

 controls or ducklings from parents fed 

 0.5 ppm mercury. 



Mallards whose parents were fed a diet con- 

 taining 0.5 ppm mercury (dry weight) were 

 themselves fed a diet containing 0.5 ppm mer- 

 cury (dry weight) from 9 days of age through 

 their first reproductive season (Heinz 1976c). 

 Mercury in the eggs of these hens fed mercury 



