Feathers, Fur and Skin
Oil physically alters a bird's feather structure. A bird can't maintain body heat with feathers that cannot trap air and repel water. As a result, the bird may become hypothermic. The bird's metabolism increases, causing a greater need for food, but it cannot float or fly, decreasing its ability to locate food. When a marine mammal is exposed to oil, the hairs are altered and the air layer that insulated the mammal from cold ocean water is destroyed. Similar to the bird, the mammal will have problems with hypothermia.
Internal Damage
Injested oil can cause damage to the gastrointestinal tract of birds and marine mammals. Birds may experience ulcers, diarrhea, pneumonia, neurological damage or cancer. Oil such as jet fuel can cause birds to have anemia and the lack the cells to combat infection. Birds and marine mammals may experience damage to the kidneys and liver. Fumes can irritate the respiratory tract, causing pnuemonia and inflammation. Marine mammals, such as sea otters, that spend a great deal of time grooming are at risk of injesting oils from the haircoat.
Breeding
A single drop of oil on eggs creates significant mortality and developmental defects in bird embryos. Oil contamination causes an increased rate of abandonment of hatchlings by adult birds, as well as changes in breeding activities. Exposure to oil has caused decreased birthrates in marine mammals for several generations.
Mortality
Many animals affected by oil may die while in rehabilitation. Birds are given leg bands and marine mammals are marked prior to release from some rehabilitation centers, but it is costly and time consuming to track them. It is difficult to determine the survival rate of oiled animals that have been rehabilitated. Studies have shown that oil exposure to wildlife may affect behavior, reproduction, overall health and biological functions.