suffer the risk of emerging into it and thus becoming severely contaminated 

 (Bourne 1968b). Other species may actively avoid oil; Hainard (1959) reported 

 that some diving ducks (Tufted Duck [ Aythya fuligula ] and Pochard [A. ferina ]) 

 avoid patches of oil floating down a river. Other, more aerial species such as 

 gulls (Bourne 1968b) and Manx Shearwaters ( Puffinus puff inus ) (Casement 1966) 

 may also actively avoid at least the thicker, more noticeable oil slicks. Some 

 of these birds evidently avoid oil when swimming as well; a Herring Gull ( Larus 

 argentatus ) and a Black-legged Kittiwake ( Rissa tridactyla ) that swam into a 

 patch of floating oil immediately took flight (Bourne 1968b, Bourne and Devlin 

 1969). 



The number of birds that die following an oil spill is also related to the 

 type of petroleum that was spilled and how long it has been in the environment. 

 Crude oil is less toxic than refined oils (diesel oil, No. 2 fuel oil, Bunker 

 "C")(Hay 1979), and fresh oil causes more damage than older, more weathered oils 

 (Bourne and Bibby 1975). Some oils may be innocuous enough that oiled birds are 

 not killed and are even capable of cleaning their plumage (Birkhead et al. 1973, 

 Phillips 1974). 



The number of deaths from oiling following a spill is not necessarily re- 

 lated to the amount of oil spilled; large spills may result in relatively few 

 deaths, while smaller spills may cause large losses, particularly when substan- 

 tial numbers of birds are concentrated in small areas (Croxall 1975, Salomonsen 

 1979). In addition, large catastrophic oil spills may cause no greater loss of 

 marine birds than does chronic oil pollution of the environment (Nelson-Smith 

 1973, Croxall 1975, Holmes and Cronshaw 1977). 



EFFECTS OF OIL ON CONTAMINATED BIRDS AND THEIR EGGS 



The primary effect of oil on birds is to cause a loss of buoyancy and insu- 

 lation when the feathers become matted (Szaro 1977). This increases the meta- 

 bolic demand to maintain body heat and in cold weather quickly results in chil- 

 ling. The increased physical effort to remain afloat also increases the demand 

 on the body's resources, and death from exhaustion and exposure may ensue (Bourne 

 1976). McEwan and Koelink (1973) reported that heat loss of experimentally 

 oiled Mallards and scaup was 1.7 and 2 times greater, respectively, than normal. 



Ingestion of oil as the contaminated bird tries to preen its feathers will 

 usually cause further harm. A pioneer study by Hartung and Hunt (1966) showed 

 that ingestion of oil by Mallards and Black Ducks could be followed by nervous 

 disorders, enlargement of the adrenal cortex, lipid pneumonia, diarrhea, and 

 gastrointestinal irritation. A considerable number of experimental studies con- 

 ducted on marine birds in the United States were reviewed recently at length by 

 Albers (1977), Holmes and Cronshaw (1977), Szaro (1977), Eastin and Hoffman 

 (1978), Ohlendorf et al. (1978), and Stickel and Dieter (1979). Some of the 

 findings that involve both primary and secondary effects of oiling are briefly 

 summarized as follows: 



(1) Physiological effects that result from ingestion of oil include dehy- 

 dration, enteritis, fatty changes in the liver, renal tubular nephro- 

 sis, and reduction in the rates of sodium and water transfer across 



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