have helped elucidate the effects that minute amounts of oil would have dur- 

 ing the reproductive season. 



Outdoor and Field Studies 



The indoor pen studies have been invaluable, because under optimally 

 controlled environmental conditions they provided indicators of the subtle 

 types of chronic effects oil may have in natural bird populations. It is 

 highly essential, however, to show correlative effects of crude oil contami- 

 nation occurring under normal field conditions. Therefore, studies were 

 conducted to confirm effects of oil on birds under more realistic environ- 

 mental conditions. Outdoor pens were used to determine whether oil applied 

 to small pools of water used by mallards for drinking and swimming would be 

 carried on the ducks' breast feathers to the nest. Eggs of these ducks 

 became oiled, and mortality to the embryos was comparable to those incubated 

 artifically (Albers, in preparation). Additional oil-related studies have 

 been done in the field with a variety of birds. Most of this work was and 

 continues to be done by Fish and Wildlife Service personnel and to a lesser 

 extent under cooperative agreements with State universities. The effects of 

 No. 2 fuel oil on hatchability of marine and estuarine bird eggs naturally 

 incubated in the field were compared with its effects on eggs artifically 

 incubated. Eggs of three species of birds from breeding colonies on the 

 Texas coast were randomly selected, 20 pi of No. 2 fuel oil was applied to 

 the eggshell surface, and the eggs were returned to the nest. After 5 days 

 of natural incubation, embryo mortality was determined. No. 2 fuel oil pro- 

 duced 56% or greater mortality in this study, only slightly less than that 

 in eggs artificially incubated (White, King, and Coon 1979). In other field 

 studies, nesting marine birds were trapped, oil was applied to their breast 

 feathers, and the birds were released. After some preening and swimming, 

 these birds returned to their nests and continued incubating their eggs. 

 Again, embryo mortality was similar to that in the incubator studies (King 

 and Lefever, in preparation). These studies under natural conditions indi- 

 cated that birds with oiled breast feathers return to their nests and con- 

 taminate the eggs they incubate. Literature reports and personal communica- 

 tions with biologists responding to oil spills include accounts of birds 

 foraging in oil -contaminated areas and collecting oil on their breast 

 feathers. Although not as well documented, bird nests containing oiled eggs 

 also have been observed after oil spills occurred near breeding areas 

 (Alexander et al . 1978). These kinds of observations need further documenta- 

 tion to assess the frequency of their occurrence. 



SUMMARY 



The results from the laboratory studies done at the Patuxent Center have 

 shown the developmental stages to be extremely susceptible to the effects of 

 low-level oil contamination. Although adult ducks may be able to physio- 

 logically compensate for oil in the diet, evidence suggests a lowered 

 tolerance to a second environmental challenge. There is also some evidence 

 that chronic ingestion of small amounts of oil by adult female ducks affects 



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