At an individual level wildlife can be affected by oil via:

• external contamination, in which the oil causes skin burns or changes the condition and physical properties of feathers or fur
• internal contamination (after inhalation or swallowing), in which the oil may cause internal burns or disturb physiolocical processes.

At the population level wildlife can be affected if the oil spill causes a significant mortality within the so called breeding stock of a population, i.e. the number of adults that contribute to the reproduction process.