and insulating characteristics of the feathers or fur and lead to death from hypothermia. Seabirds and marine mammals may be poisoned when they ingest oil during the course of trying to remove it from their feathers or pelage, or when it adheres to food items. Likewise, marine mammals (and possibly seabirds) may inhale toxic doses of petroleum vapor when at the surface in the vicinity of an oil spill (Geraci, 1990; Geraci and Williams, 1990; St. Aubin, 1990a), although there appear to be few data indicating that this is an important source of mortality (Figure 5-5). In some cases, these upper trophic level predators may become exposed to oil by ingesting prey that have oil or its metabolites in their tissues. Seabirds can transfer oil from their feathers to the surface of their eggs during incubation. Depending on the type of oil on the feathers and the presence of toxic components, embryos in the affected eggs may fail to develop. Oil can also indirectly affect the survival or reproductive success of marine birds and mammals by affecting the distribution, abundance or availability of prey.
In seabirds, ingestion of oil or oil-contaminated prey may lead to immuno-suppression and Heinz-body hemolytic anemia which compromises the ability of the blood to carry oxygen (Leighton et al., 1983; Fry and Addiego, 1987). This effect persists long after the birds appear to have recovered from exposure (Fry and Addiego, 1987). Diminished oxygen transport capacity in the blood is a particular problem for species of birds that obtain their food by pursuing prey underwater. Although the effects of the anemia have yet to be demonstrated in the field (Nisbet, 1994), seabird survival post-oiling, with or without cleaning, may be compromised. Marine mammals are also vulnerable to the toxic effects of ingested oil, and species of marine mammals such as sea otters that depend on a clean pellage for insulation are also vulnerable to surface oiling (Geraci and St. Aubin, 1987; Geraci, 1990; Geraci and Williams, 1990; St. Aubin, 1990a,b; St. Aubin and Lounsbury, 1990). Effects may be exacerbated by stress resulting from handling during cleaning (Briggs et al., 1996).
The number of seabirds killed and the damage to local populations in a spill is more likely to be determined by location and timing of the spill than by its size (Hunt, 1987; Burger, 1993). Burger found a statistically significant but