indirectly by killing their food supply. Direct mortality may occur when 

 birds are under unusual physiological stress and fats are being mobilized 

 (Ohlendorf et al. 1978b). Stress occurs during migration, periods of food 

 shortage (especially in winter when intertidal flats are ice-covered) , during 

 reproduction, disease or injury, and after exposure to oil or other 

 environmental hazards. Female eiders may be particularly vulnerable because 

 they do not feed during incubation. Dead eiders with high concentrations of 

 DDT were found on nests in the Netherlands (Howe et al. 1978). Females of 

 most species may be vulnerable during the egg-laying period because fat 

 reserves are used for egg synthesis. 



Heavy metals . Heavy metals in the environment, particularly mercury and 

 lead, have caused biologists to be concerned about effects on birds. Mercury 

 enters the environment through a variety of sources, including fungicides, 

 germicides, industrial uses, heating or burning of fuels and ores, and from 

 oil discharges from ships and refining industries (Merlini 1971; and Howe et 

 al. 1978). The most toxic form is methyl mercury (Westoo 1967; and Fimreite 

 1974). Mercury may accumulate in birds as it passes through the food web. In 

 Maine it is found in eels, mergansers, and eagles (see chapter 15, 

 "Waterfowl"). It probably occurs in other waterbirds that feed extensively on 

 eels, or those (such as herons) that feed on the same prey as eels. 



Lead enters the environment mostly from industrial, automotive, and municipal 

 sources and from lead shot (Howe et al. 1978). Waterfowl mortality from lead 

 poisoning may reach between 1.5 and 2 million birds each year in the United 

 States (Banks 1979). Lead is not known to accumulate in food chains. Eagles 

 may injest lead shot from the flesh of their prey, usually ducks. 



Plastic and other artifacts . Small particulate pollution composed mostly 

 of plastic beads and irregular shaped particulates up to 0.2 inches (0.5 cm) 

 in diameter is commonly found in plankton samples and is found in the stomachs 

 of birds and fish that feed on plankton (e.g., plastic has been found in 

 Leach's storm petrels in New Brunswick) and birds that feed on plankton- 

 feeding fish. The effects on birds are relatively unknown but intestinal 

 blockage may be one possible consequence (Ohlendorf et al. 1978a). Small 

 rubber thread cuttings are often ingested by common puffins who mistake them 

 for fish (Ohlendorf et al. 1978a). These may accumulate into entangled balls 

 of rubber in the gizzard. 



Larger waste materials are problems along beaches where birds may become 

 entangled in kite strings, fishing lines, plastic containers, and "six-pack" 

 containers. The wrack line is often the source of many potential hazards. 

 Birds foraging in dumps may also encounter these hazards. In one common tern 

 colony in New York 14 young and 7 adults were found trapped by kite strings 

 (Howe et al. 1978). The magnitude of these problems in Maine has not been 

 investigated but several instances of entangled birds have been observed. 



Other Disturbance 



Disturbance by people has the greatest adverse impact on a nesting colony. 

 Picnicking, bird watching, nature tours, and other activities disturb nesting 

 waterbirds. Deliberate vandalism, of course, has the most injurious effect of 

 all. Eggs and young are vulnerable to predation (Drury 1973; Hunt 1972; 

 Nisbet 1973; Mendall 1976; and Robert and Ralph 1975), chilling and 



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